From 7c9dc3406f085be5e3947f7dad322d91e245a202 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wwigham@gmail.com>
Date: Fri, 9 Apr 2021 15:21:33 -0700
Subject: [PATCH 1/6] Relate non-augmenting array subtypes without resorting to
 structural comparison

---
 src/compiler/checker.ts                       | 34 +++++++++++++++++++
 .../reference/arrayLiterals3.errors.txt       |  4 +--
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 530e734a552a2..b601c7a9153dd 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -18219,6 +18219,22 @@ namespace ts {
                     return result;
                 }
 
+                if (isNonAugmentingArraySubtype(source) && isArrayType(target)) {
+                    let sourceBase = getBaseTypes((source as TypeReference).target as InterfaceType)[0];
+                    if (length((target as TypeReference).resolvedTypeArguments) === 2) {
+                        sourceBase = getTypeWithThisArgument(sourceBase, ((source as TypeReference).target as InterfaceType).thisType);
+                    }
+                    return isRelatedTo(sourceBase, target, reportErrors);
+                }
+
+                if (isArrayType(source) && isNonAugmentingArraySubtype(target)) {
+                    let targetBase = getBaseTypes((target as TypeReference).target as InterfaceType)[0];
+                    if (length((source as TypeReference).resolvedTypeArguments) === 2) {
+                        targetBase = getTypeWithThisArgument(targetBase, ((target as TypeReference).target as InterfaceType).thisType);
+                    }
+                    return isRelatedTo(source, targetBase, reportErrors);
+                }
+
                 if (target.flags & TypeFlags.TypeParameter) {
                     // A source type { [P in Q]: X } is related to a target type T if keyof T is related to Q and X is related to T[Q].
                     if (getObjectFlags(source) & ObjectFlags.Mapped && !(<MappedType>source).declaration.nameType && isRelatedTo(getIndexType(target), getConstraintTypeFromMappedType(<MappedType>source))) {
@@ -19868,6 +19884,24 @@ namespace ts {
             return isArrayType(type) || !(type.flags & TypeFlags.Nullable) && isTypeAssignableTo(type, anyReadonlyArrayType);
         }
 
+        function isNonAugmentingArraySubtype(type: Type) {
+            if (!(getObjectFlags(type) & ObjectFlags.Reference) || !(getObjectFlags((type as TypeReference).target) & ObjectFlags.ClassOrInterface)) {
+                return false;
+            }
+            const target = (type as TypeReference).target as InterfaceType;
+            const bases = getBaseTypes(target);
+            if (bases.length !== 1) {
+                return false;
+            }
+            if (!isArrayType(bases[0])) {
+                return false;
+            }
+            if (getMembersOfSymbol(type.symbol).size) {
+                return false; // If the interface has any members, they may subtype members in the base, so we should do a full structural comparison
+            }
+            return true;
+        }
+
         function isEmptyArrayLiteralType(type: Type): boolean {
             const elementType = getElementTypeOfArrayType(type);
             return strictNullChecks ? elementType === implicitNeverType : elementType === undefinedWideningType;
diff --git a/tests/baselines/reference/arrayLiterals3.errors.txt b/tests/baselines/reference/arrayLiterals3.errors.txt
index 8ea3d1583b6fb..782983eb9884d 100644
--- a/tests/baselines/reference/arrayLiterals3.errors.txt
+++ b/tests/baselines/reference/arrayLiterals3.errors.txt
@@ -8,7 +8,7 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(17,5): error
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(33,5): error TS2322: Type 'number[]' is not assignable to type '[number, number, number]'.
   Target requires 3 element(s) but source may have fewer.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error TS2322: Type '(string | number)[]' is not assignable to type 'myArray'.
-  The types returned by 'pop()' are incompatible between these types.
+  Type '(string | number)[]' is not assignable to type 'Number[]'.
     Type 'string | number' is not assignable to type 'Number'.
       Type 'string' is not assignable to type 'Number'.
 
@@ -65,7 +65,7 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
     var c2: myArray = [...temp1, ...temp];            // Error cannot assign (number|string)[] to number[]
         ~~
 !!! error TS2322: Type '(string | number)[]' is not assignable to type 'myArray'.
-!!! error TS2322:   The types returned by 'pop()' are incompatible between these types.
+!!! error TS2322:   Type '(string | number)[]' is not assignable to type 'Number[]'.
 !!! error TS2322:     Type 'string | number' is not assignable to type 'Number'.
 !!! error TS2322:       Type 'string' is not assignable to type 'Number'.
     
\ No newline at end of file

From f1cff54075ff298e5cba987c28ad3cd10a152e3e Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wwigham@gmail.com>
Date: Fri, 9 Apr 2021 15:32:05 -0700
Subject: [PATCH 2/6] Fix lint

---
 src/compiler/checker.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index b601c7a9153dd..2929b688af71e 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -18221,7 +18221,7 @@ namespace ts {
 
                 if (isNonAugmentingArraySubtype(source) && isArrayType(target)) {
                     let sourceBase = getBaseTypes((source as TypeReference).target as InterfaceType)[0];
-                    if (length((target as TypeReference).resolvedTypeArguments) === 2) {
+                    if (length(target.resolvedTypeArguments) === 2) {
                         sourceBase = getTypeWithThisArgument(sourceBase, ((source as TypeReference).target as InterfaceType).thisType);
                     }
                     return isRelatedTo(sourceBase, target, reportErrors);
@@ -18229,7 +18229,7 @@ namespace ts {
 
                 if (isArrayType(source) && isNonAugmentingArraySubtype(target)) {
                     let targetBase = getBaseTypes((target as TypeReference).target as InterfaceType)[0];
-                    if (length((source as TypeReference).resolvedTypeArguments) === 2) {
+                    if (length(source.resolvedTypeArguments) === 2) {
                         targetBase = getTypeWithThisArgument(targetBase, ((target as TypeReference).target as InterfaceType).thisType);
                     }
                     return isRelatedTo(source, targetBase, reportErrors);

From 15796c943c359c0abb4d4c3dcda26c44b3e003bc Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wwigham@gmail.com>
Date: Wed, 14 Apr 2021 13:48:58 -0700
Subject: [PATCH 3/6] Generalize performance enhancement

---
 src/compiler/checker.ts                       | 29 +++++++++----------
 ...tWithObjectMembersAccessibility.errors.txt | 24 +++++++--------
 .../checkJsxChildrenProperty5.errors.txt      |  6 ++--
 .../checkJsxChildrenProperty7.errors.txt      |  2 ++
 .../classImplementsClass4.errors.txt          |  6 ++--
 .../classImplementsClass5.errors.txt          | 12 +++++---
 ...ertyIsRelatableToTargetProperty.errors.txt |  6 ++--
 ...aceExtendingClassWithProtecteds.errors.txt |  6 ++--
 .../reference/inheritance1.errors.txt         | 19 +++++++-----
 ...andParentPrivateMemberCollision.errors.txt |  6 ++--
 ...MemberCollisionWithPublicMember.errors.txt |  6 ++--
 ...emberCollisionWithPrivateMember.errors.txt |  6 ++--
 .../interfaceImplementation8.errors.txt       | 12 +++++---
 .../reference/privateNamesUnique-4.errors.txt |  6 ++--
 .../reference/privateNamesUnique-5.errors.txt |  6 ++--
 .../recursiveComplicatedClasses.types         |  2 +-
 ...elessFunctionComponentOverload4.errors.txt |  2 ++
 17 files changed, 94 insertions(+), 62 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 20373d05d0671..5b949b8b6823d 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -18219,18 +18219,18 @@ namespace ts {
                     return result;
                 }
 
-                if (isNonAugmentingArraySubtype(source) && isArrayType(target)) {
-                    let sourceBase = getBaseTypes((source as TypeReference).target as InterfaceType)[0];
-                    if (length(target.resolvedTypeArguments) === 2) {
-                        sourceBase = getTypeWithThisArgument(sourceBase, ((source as TypeReference).target as InterfaceType).thisType);
+                let sourceBase = getSingleBaseForNonAugmentingSubtype(source);
+                if (sourceBase) {
+                    if (getObjectFlags(target) & ObjectFlags.Reference && length(getTypeArguments((target as TypeReference))) > length((target as TypeReference).target.typeParameters)) {
+                        sourceBase = getTypeWithThisArgument(sourceBase, last(getTypeArguments(source as TypeReference)));
                     }
                     return isRelatedTo(sourceBase, target, reportErrors);
                 }
 
-                if (isArrayType(source) && isNonAugmentingArraySubtype(target)) {
-                    let targetBase = getBaseTypes((target as TypeReference).target as InterfaceType)[0];
-                    if (length(source.resolvedTypeArguments) === 2) {
-                        targetBase = getTypeWithThisArgument(targetBase, ((target as TypeReference).target as InterfaceType).thisType);
+                let targetBase = getSingleBaseForNonAugmentingSubtype(target);
+                if (targetBase) {
+                    if (getObjectFlags(source) & ObjectFlags.Reference && length(getTypeArguments((source as TypeReference))) > length((source as TypeReference).target.typeParameters)) {
+                        targetBase = getTypeWithThisArgument(targetBase, last(getTypeArguments(target as TypeReference)));
                     }
                     return isRelatedTo(source, targetBase, reportErrors);
                 }
@@ -19917,22 +19917,19 @@ namespace ts {
             return isArrayType(type) || !(type.flags & TypeFlags.Nullable) && isTypeAssignableTo(type, anyReadonlyArrayType);
         }
 
-        function isNonAugmentingArraySubtype(type: Type) {
+        function getSingleBaseForNonAugmentingSubtype(type: Type) {
             if (!(getObjectFlags(type) & ObjectFlags.Reference) || !(getObjectFlags((type as TypeReference).target) & ObjectFlags.ClassOrInterface)) {
-                return false;
+                return undefined;
             }
             const target = (type as TypeReference).target as InterfaceType;
             const bases = getBaseTypes(target);
             if (bases.length !== 1) {
-                return false;
-            }
-            if (!isArrayType(bases[0])) {
-                return false;
+                return undefined;
             }
             if (getMembersOfSymbol(type.symbol).size) {
-                return false; // If the interface has any members, they may subtype members in the base, so we should do a full structural comparison
+                return undefined; // If the interface has any members, they may subtype members in the base, so we should do a full structural comparison
             }
-            return true;
+            return !length(target.typeParameters) ? bases[0] : instantiateType(bases[0], createTypeMapper(target.typeParameters!, getTypeArguments(type as TypeReference).slice(0, target.typeParameters!.length)));
         }
 
         function isEmptyArrayLiteralType(type: Type): boolean {
diff --git a/tests/baselines/reference/assignmentCompatWithObjectMembersAccessibility.errors.txt b/tests/baselines/reference/assignmentCompatWithObjectMembersAccessibility.errors.txt
index c1093ab0ffe87..93774cefaa52c 100644
--- a/tests/baselines/reference/assignmentCompatWithObjectMembersAccessibility.errors.txt
+++ b/tests/baselines/reference/assignmentCompatWithObjectMembersAccessibility.errors.txt
@@ -17,7 +17,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(81,5): error TS2322: Type 'Base' is not assignable to type '{ foo: string; }'.
   Property 'foo' is private in type 'Base' but not in type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(82,5): error TS2322: Type 'I' is not assignable to type '{ foo: string; }'.
-  Property 'foo' is private in type 'I' but not in type '{ foo: string; }'.
+  Type 'Base' is not assignable to type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(84,5): error TS2322: Type 'E' is not assignable to type '{ foo: string; }'.
   Property 'foo' is private in type 'E' but not in type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(86,5): error TS2322: Type '{ foo: string; }' is not assignable to type 'Base'.
@@ -27,15 +27,15 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(89,5): error TS2322: Type 'E' is not assignable to type 'Base'.
   Types have separate declarations of a private property 'foo'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(92,5): error TS2322: Type '{ foo: string; }' is not assignable to type 'I'.
-  Property 'foo' is private in type 'I' but not in type '{ foo: string; }'.
+  Type '{ foo: string; }' is not assignable to type 'Base'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(94,5): error TS2322: Type 'D' is not assignable to type 'I'.
-  Property 'foo' is private in type 'I' but not in type 'D'.
+  Type 'D' is not assignable to type 'Base'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(95,5): error TS2322: Type 'E' is not assignable to type 'I'.
-  Types have separate declarations of a private property 'foo'.
+  Type 'E' is not assignable to type 'Base'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(99,5): error TS2322: Type 'Base' is not assignable to type 'D'.
   Property 'foo' is private in type 'Base' but not in type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(100,5): error TS2322: Type 'I' is not assignable to type 'D'.
-  Property 'foo' is private in type 'I' but not in type 'D'.
+  Type 'Base' is not assignable to type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(101,5): error TS2322: Type 'E' is not assignable to type 'D'.
   Property 'foo' is private in type 'E' but not in type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(103,5): error TS2322: Type '{ foo: string; }' is not assignable to type 'E'.
@@ -43,7 +43,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(104,5): error TS2322: Type 'Base' is not assignable to type 'E'.
   Types have separate declarations of a private property 'foo'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(105,5): error TS2322: Type 'I' is not assignable to type 'E'.
-  Types have separate declarations of a private property 'foo'.
+  Type 'Base' is not assignable to type 'E'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(106,5): error TS2322: Type 'D' is not assignable to type 'E'.
   Property 'foo' is private in type 'E' but not in type 'D'.
 
@@ -160,7 +160,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a = i; // error
         ~
 !!! error TS2322: Type 'I' is not assignable to type '{ foo: string; }'.
-!!! error TS2322:   Property 'foo' is private in type 'I' but not in type '{ foo: string; }'.
+!!! error TS2322:   Type 'Base' is not assignable to type '{ foo: string; }'.
         a = d;
         a = e; // error
         ~
@@ -185,16 +185,16 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         i = a; // error
         ~
 !!! error TS2322: Type '{ foo: string; }' is not assignable to type 'I'.
-!!! error TS2322:   Property 'foo' is private in type 'I' but not in type '{ foo: string; }'.
+!!! error TS2322:   Type '{ foo: string; }' is not assignable to type 'Base'.
         i = b;
         i = d; // error
         ~
 !!! error TS2322: Type 'D' is not assignable to type 'I'.
-!!! error TS2322:   Property 'foo' is private in type 'I' but not in type 'D'.
+!!! error TS2322:   Type 'D' is not assignable to type 'Base'.
         i = e; // error
         ~
 !!! error TS2322: Type 'E' is not assignable to type 'I'.
-!!! error TS2322:   Types have separate declarations of a private property 'foo'.
+!!! error TS2322:   Type 'E' is not assignable to type 'Base'.
         i = i;
     
         d = a;
@@ -205,7 +205,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         d = i; // error
         ~
 !!! error TS2322: Type 'I' is not assignable to type 'D'.
-!!! error TS2322:   Property 'foo' is private in type 'I' but not in type 'D'.
+!!! error TS2322:   Type 'Base' is not assignable to type 'D'.
         d = e; // error
         ~
 !!! error TS2322: Type 'E' is not assignable to type 'D'.
@@ -222,7 +222,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         e = i; // errror
         ~
 !!! error TS2322: Type 'I' is not assignable to type 'E'.
-!!! error TS2322:   Types have separate declarations of a private property 'foo'.
+!!! error TS2322:   Type 'Base' is not assignable to type 'E'.
         e = d; // errror
         ~
 !!! error TS2322: Type 'D' is not assignable to type 'E'.
diff --git a/tests/baselines/reference/checkJsxChildrenProperty5.errors.txt b/tests/baselines/reference/checkJsxChildrenProperty5.errors.txt
index 476644ee33603..7f351d9aacd43 100644
--- a/tests/baselines/reference/checkJsxChildrenProperty5.errors.txt
+++ b/tests/baselines/reference/checkJsxChildrenProperty5.errors.txt
@@ -1,5 +1,6 @@
 tests/cases/conformance/jsx/file.tsx(20,10): error TS2741: Property 'children' is missing in type '{ a: number; b: string; }' but required in type 'Prop'.
-tests/cases/conformance/jsx/file.tsx(25,9): error TS2740: Type 'Element' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
+tests/cases/conformance/jsx/file.tsx(25,9): error TS2322: Type 'Element' is not assignable to type 'Button'.
+  Type 'ReactElement<any>' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
 tests/cases/conformance/jsx/file.tsx(29,10): error TS2740: Type 'typeof Button' is missing the following properties from type 'Button': render, setState, forceUpdate, props, and 3 more.
 
 
@@ -33,7 +34,8 @@ tests/cases/conformance/jsx/file.tsx(29,10): error TS2740: Type 'typeof Button'
         <Comp a={10} b="hi">
             <Button />
             ~~~~~~~~~~
-!!! error TS2740: Type 'Element' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
+!!! error TS2322: Type 'Element' is not assignable to type 'Button'.
+!!! error TS2322:   Type 'ReactElement<any>' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
 !!! related TS6500 tests/cases/conformance/jsx/file.tsx:6:5: The expected type comes from property 'children' which is declared here on type 'IntrinsicAttributes & Prop'
         </Comp>;
     let k2 =
diff --git a/tests/baselines/reference/checkJsxChildrenProperty7.errors.txt b/tests/baselines/reference/checkJsxChildrenProperty7.errors.txt
index 0197bc6cd413e..d5d10f11a2e68 100644
--- a/tests/baselines/reference/checkJsxChildrenProperty7.errors.txt
+++ b/tests/baselines/reference/checkJsxChildrenProperty7.errors.txt
@@ -1,4 +1,5 @@
 tests/cases/conformance/jsx/file.tsx(24,40): error TS2747: 'Comp' components don't accept text as child elements. Text in JSX has the type 'string', but the expected type of 'children' is 'Element | Element[]'.
+  Type 'string' is not assignable to type 'ReactElement<any>'.
 tests/cases/conformance/jsx/file.tsx(26,22): error TS2747: 'Comp' components don't accept text as child elements. Text in JSX has the type 'string', but the expected type of 'children' is 'Element | Element[]'.
 tests/cases/conformance/jsx/file.tsx(27,30): error TS2747: 'Comp' components don't accept text as child elements. Text in JSX has the type 'string', but the expected type of 'children' is 'Element | Element[]'.
 
@@ -30,6 +31,7 @@ tests/cases/conformance/jsx/file.tsx(27,30): error TS2747: 'Comp' components don
     let k1 = <Comp a={10} b="hi"><Button />  <AnotherButton /></Comp>;
                                            ~~
 !!! error TS2747: 'Comp' components don't accept text as child elements. Text in JSX has the type 'string', but the expected type of 'children' is 'Element | Element[]'.
+!!! error TS2747:   Type 'string' is not assignable to type 'ReactElement<any>'.
     let k2 = <Comp a={10} b="hi"><Button />
         <AnotherButton />  </Comp>;
                          ~~
diff --git a/tests/baselines/reference/classImplementsClass4.errors.txt b/tests/baselines/reference/classImplementsClass4.errors.txt
index 9cb8b9dd1bae5..60a3c0b0eafbf 100644
--- a/tests/baselines/reference/classImplementsClass4.errors.txt
+++ b/tests/baselines/reference/classImplementsClass4.errors.txt
@@ -1,6 +1,7 @@
 tests/cases/compiler/classImplementsClass4.ts(5,7): error TS2720: Class 'C' incorrectly implements class 'A'. Did you mean to extend 'A' and inherit its members as a subclass?
   Property 'x' is missing in type 'C' but required in type 'A'.
-tests/cases/compiler/classImplementsClass4.ts(16,1): error TS2741: Property 'x' is missing in type 'C' but required in type 'C2'.
+tests/cases/compiler/classImplementsClass4.ts(16,1): error TS2322: Type 'C' is not assignable to type 'C2'.
+  Property 'x' is missing in type 'C' but required in type 'A'.
 
 
 ==== tests/cases/compiler/classImplementsClass4.ts (2 errors) ====
@@ -25,5 +26,6 @@ tests/cases/compiler/classImplementsClass4.ts(16,1): error TS2741: Property 'x'
     c = c2;
     c2 = c;
     ~~
-!!! error TS2741: Property 'x' is missing in type 'C' but required in type 'C2'.
+!!! error TS2322: Type 'C' is not assignable to type 'C2'.
+!!! error TS2322:   Property 'x' is missing in type 'C' but required in type 'A'.
 !!! related TS2728 tests/cases/compiler/classImplementsClass4.ts:2:13: 'x' is declared here.
\ No newline at end of file
diff --git a/tests/baselines/reference/classImplementsClass5.errors.txt b/tests/baselines/reference/classImplementsClass5.errors.txt
index a291da15407bc..00c789ac6651a 100644
--- a/tests/baselines/reference/classImplementsClass5.errors.txt
+++ b/tests/baselines/reference/classImplementsClass5.errors.txt
@@ -1,9 +1,11 @@
 tests/cases/compiler/classImplementsClass5.ts(5,7): error TS2720: Class 'C' incorrectly implements class 'A'. Did you mean to extend 'A' and inherit its members as a subclass?
   Types have separate declarations of a private property 'x'.
 tests/cases/compiler/classImplementsClass5.ts(16,1): error TS2322: Type 'C2' is not assignable to type 'C'.
-  Types have separate declarations of a private property 'x'.
+  Type 'A' is not assignable to type 'C'.
+    Types have separate declarations of a private property 'x'.
 tests/cases/compiler/classImplementsClass5.ts(17,1): error TS2322: Type 'C' is not assignable to type 'C2'.
-  Types have separate declarations of a private property 'x'.
+  Type 'C' is not assignable to type 'A'.
+    Types have separate declarations of a private property 'x'.
 
 
 ==== tests/cases/compiler/classImplementsClass5.ts (3 errors) ====
@@ -28,8 +30,10 @@ tests/cases/compiler/classImplementsClass5.ts(17,1): error TS2322: Type 'C' is n
     c = c2;
     ~
 !!! error TS2322: Type 'C2' is not assignable to type 'C'.
-!!! error TS2322:   Types have separate declarations of a private property 'x'.
+!!! error TS2322:   Type 'A' is not assignable to type 'C'.
+!!! error TS2322:     Types have separate declarations of a private property 'x'.
     c2 = c;
     ~~
 !!! error TS2322: Type 'C' is not assignable to type 'C2'.
-!!! error TS2322:   Types have separate declarations of a private property 'x'.
\ No newline at end of file
+!!! error TS2322:   Type 'C' is not assignable to type 'A'.
+!!! error TS2322:     Types have separate declarations of a private property 'x'.
\ No newline at end of file
diff --git a/tests/baselines/reference/crashInsourcePropertyIsRelatableToTargetProperty.errors.txt b/tests/baselines/reference/crashInsourcePropertyIsRelatableToTargetProperty.errors.txt
index 2fd1cc7e831c3..d57411e508c43 100644
--- a/tests/baselines/reference/crashInsourcePropertyIsRelatableToTargetProperty.errors.txt
+++ b/tests/baselines/reference/crashInsourcePropertyIsRelatableToTargetProperty.errors.txt
@@ -1,4 +1,5 @@
-tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts(9,5): error TS2741: Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'D'.
+tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts(9,5): error TS2322: Type '(x: "hi", items: string[]) => typeof foo' is not assignable to type 'D'.
+  Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'C'.
 
 
 ==== tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts (1 errors) ====
@@ -12,6 +13,7 @@ tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts(9,5): e
     }
     var a: D = foo("hi", []);
         ~
-!!! error TS2741: Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'D'.
+!!! error TS2322: Type '(x: "hi", items: string[]) => typeof foo' is not assignable to type 'D'.
+!!! error TS2322:   Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'C'.
 !!! related TS2728 tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts:2:13: 'x' is declared here.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/implementingAnInterfaceExtendingClassWithProtecteds.errors.txt b/tests/baselines/reference/implementingAnInterfaceExtendingClassWithProtecteds.errors.txt
index ecb3e4664a470..215af9421d584 100644
--- a/tests/baselines/reference/implementingAnInterfaceExtendingClassWithProtecteds.errors.txt
+++ b/tests/baselines/reference/implementingAnInterfaceExtendingClassWithProtecteds.errors.txt
@@ -7,7 +7,8 @@ tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInte
 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts(21,7): error TS2420: Class 'Bar4' incorrectly implements interface 'I'.
   Property 'x' is protected but type 'Bar4' is not a class derived from 'Foo'.
 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts(26,7): error TS2420: Class 'Bar5' incorrectly implements interface 'I'.
-  Property 'y' is missing in type 'Bar5' but required in type 'I'.
+  Type 'Foo' is not assignable to type 'I'.
+    Property 'y' is missing in type 'Foo' but required in type 'I'.
 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts(29,7): error TS2420: Class 'Bar6' incorrectly implements interface 'I'.
   Property 'y' is protected in type 'Bar6' but public in type 'I'.
 
@@ -54,7 +55,8 @@ tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInte
     class Bar5 extends Foo implements I { // error
           ~~~~
 !!! error TS2420: Class 'Bar5' incorrectly implements interface 'I'.
-!!! error TS2420:   Property 'y' is missing in type 'Bar5' but required in type 'I'.
+!!! error TS2420:   Type 'Foo' is not assignable to type 'I'.
+!!! error TS2420:     Property 'y' is missing in type 'Foo' but required in type 'I'.
 !!! related TS2728 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts:6:5: 'y' is declared here.
     }
     
diff --git a/tests/baselines/reference/inheritance1.errors.txt b/tests/baselines/reference/inheritance1.errors.txt
index de5e1c6d0dfbb..f7223fdfd4adc 100644
--- a/tests/baselines/reference/inheritance1.errors.txt
+++ b/tests/baselines/reference/inheritance1.errors.txt
@@ -1,11 +1,14 @@
 tests/cases/compiler/inheritance1.ts(14,7): error TS2420: Class 'ImageBase' incorrectly implements interface 'SelectableControl'.
-  Property 'select' is missing in type 'ImageBase' but required in type 'SelectableControl'.
+  Type 'Control' is not assignable to type 'SelectableControl'.
+    Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
 tests/cases/compiler/inheritance1.ts(18,7): error TS2420: Class 'Locations' incorrectly implements interface 'SelectableControl'.
   Property 'state' is missing in type 'Locations' but required in type 'SelectableControl'.
 tests/cases/compiler/inheritance1.ts(31,1): error TS2741: Property 'select' is missing in type 'Control' but required in type 'Button'.
 tests/cases/compiler/inheritance1.ts(37,1): error TS2741: Property 'select' is missing in type 'Control' but required in type 'TextBox'.
-tests/cases/compiler/inheritance1.ts(40,1): error TS2741: Property 'select' is missing in type 'ImageBase' but required in type 'SelectableControl'.
-tests/cases/compiler/inheritance1.ts(46,1): error TS2741: Property 'select' is missing in type 'Image1' but required in type 'SelectableControl'.
+tests/cases/compiler/inheritance1.ts(40,1): error TS2322: Type 'ImageBase' is not assignable to type 'SelectableControl'.
+  Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
+tests/cases/compiler/inheritance1.ts(46,1): error TS2322: Type 'Image1' is not assignable to type 'SelectableControl'.
+  Type 'Control' is not assignable to type 'SelectableControl'.
 tests/cases/compiler/inheritance1.ts(52,1): error TS2741: Property 'state' is missing in type 'Locations' but required in type 'SelectableControl'.
 tests/cases/compiler/inheritance1.ts(53,1): error TS2741: Property 'state' is missing in type 'Locations' but required in type 'Control'.
 tests/cases/compiler/inheritance1.ts(55,1): error TS2741: Property 'select' is missing in type 'Control' but required in type 'Locations'.
@@ -31,7 +34,8 @@ tests/cases/compiler/inheritance1.ts(61,1): error TS2741: Property 'select' is m
     class ImageBase extends Control implements SelectableControl{
           ~~~~~~~~~
 !!! error TS2420: Class 'ImageBase' incorrectly implements interface 'SelectableControl'.
-!!! error TS2420:   Property 'select' is missing in type 'ImageBase' but required in type 'SelectableControl'.
+!!! error TS2420:   Type 'Control' is not assignable to type 'SelectableControl'.
+!!! error TS2420:     Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
 !!! related TS2728 tests/cases/compiler/inheritance1.ts:5:5: 'select' is declared here.
     }
     class Image1 extends Control {
@@ -70,7 +74,8 @@ tests/cases/compiler/inheritance1.ts(61,1): error TS2741: Property 'select' is m
     var i: ImageBase;
     sc = i;
     ~~
-!!! error TS2741: Property 'select' is missing in type 'ImageBase' but required in type 'SelectableControl'.
+!!! error TS2322: Type 'ImageBase' is not assignable to type 'SelectableControl'.
+!!! error TS2322:   Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
 !!! related TS2728 tests/cases/compiler/inheritance1.ts:5:5: 'select' is declared here.
     c = i;
     i = sc;
@@ -79,8 +84,8 @@ tests/cases/compiler/inheritance1.ts(61,1): error TS2741: Property 'select' is m
     var i1: Image1;
     sc = i1;
     ~~
-!!! error TS2741: Property 'select' is missing in type 'Image1' but required in type 'SelectableControl'.
-!!! related TS2728 tests/cases/compiler/inheritance1.ts:5:5: 'select' is declared here.
+!!! error TS2322: Type 'Image1' is not assignable to type 'SelectableControl'.
+!!! error TS2322:   Type 'Control' is not assignable to type 'SelectableControl'.
     c = i1;
     i1 = sc;
     i1 = c;
diff --git a/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollision.errors.txt b/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollision.errors.txt
index 84a04107008f7..c8d18fa915afe 100644
--- a/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollision.errors.txt
+++ b/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollision.errors.txt
@@ -1,5 +1,6 @@
 tests/cases/compiler/inheritanceGrandParentPrivateMemberCollision.ts(7,7): error TS2415: Class 'C' incorrectly extends base class 'B'.
-  Types have separate declarations of a private property 'myMethod'.
+  Type 'C' is not assignable to type 'A'.
+    Types have separate declarations of a private property 'myMethod'.
 
 
 ==== tests/cases/compiler/inheritanceGrandParentPrivateMemberCollision.ts (1 errors) ====
@@ -12,7 +13,8 @@ tests/cases/compiler/inheritanceGrandParentPrivateMemberCollision.ts(7,7): error
     class C extends B {
           ~
 !!! error TS2415: Class 'C' incorrectly extends base class 'B'.
-!!! error TS2415:   Types have separate declarations of a private property 'myMethod'.
+!!! error TS2415:   Type 'C' is not assignable to type 'A'.
+!!! error TS2415:     Types have separate declarations of a private property 'myMethod'.
         private myMethod() { }
     }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.errors.txt b/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.errors.txt
index 7486fbc6e8f5c..3febf1888744d 100644
--- a/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.errors.txt
+++ b/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.errors.txt
@@ -1,5 +1,6 @@
 tests/cases/compiler/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.ts(7,7): error TS2415: Class 'C' incorrectly extends base class 'B'.
-  Property 'myMethod' is private in type 'B' but not in type 'C'.
+  Type 'C' is not assignable to type 'A'.
+    Property 'myMethod' is private in type 'A' but not in type 'C'.
 
 
 ==== tests/cases/compiler/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.ts (1 errors) ====
@@ -12,7 +13,8 @@ tests/cases/compiler/inheritanceGrandParentPrivateMemberCollisionWithPublicMembe
     class C extends B {
           ~
 !!! error TS2415: Class 'C' incorrectly extends base class 'B'.
-!!! error TS2415:   Property 'myMethod' is private in type 'B' but not in type 'C'.
+!!! error TS2415:   Type 'C' is not assignable to type 'A'.
+!!! error TS2415:     Property 'myMethod' is private in type 'A' but not in type 'C'.
         public myMethod() { }
     }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.errors.txt b/tests/baselines/reference/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.errors.txt
index 1ef0d8c0cdbe1..561f83bf6d363 100644
--- a/tests/baselines/reference/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.errors.txt
+++ b/tests/baselines/reference/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.errors.txt
@@ -1,5 +1,6 @@
 tests/cases/compiler/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.ts(7,7): error TS2415: Class 'C' incorrectly extends base class 'B'.
-  Property 'myMethod' is private in type 'C' but not in type 'B'.
+  Type 'C' is not assignable to type 'A'.
+    Property 'myMethod' is private in type 'C' but not in type 'A'.
 
 
 ==== tests/cases/compiler/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.ts (1 errors) ====
@@ -12,7 +13,8 @@ tests/cases/compiler/inheritanceGrandParentPublicMemberCollisionWithPrivateMembe
     class C extends B {
           ~
 !!! error TS2415: Class 'C' incorrectly extends base class 'B'.
-!!! error TS2415:   Property 'myMethod' is private in type 'C' but not in type 'B'.
+!!! error TS2415:   Type 'C' is not assignable to type 'A'.
+!!! error TS2415:     Property 'myMethod' is private in type 'C' but not in type 'A'.
         private myMethod() { }
     }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/interfaceImplementation8.errors.txt b/tests/baselines/reference/interfaceImplementation8.errors.txt
index 6b4b8f4a4fa13..81898f3aacc73 100644
--- a/tests/baselines/reference/interfaceImplementation8.errors.txt
+++ b/tests/baselines/reference/interfaceImplementation8.errors.txt
@@ -1,9 +1,11 @@
 tests/cases/compiler/interfaceImplementation8.ts(12,7): error TS2420: Class 'C2' incorrectly implements interface 'i1'.
   Property 'name' is private in type 'C2' but not in type 'i1'.
 tests/cases/compiler/interfaceImplementation8.ts(21,7): error TS2420: Class 'C5' incorrectly implements interface 'i1'.
-  Property 'name' is private in type 'C5' but not in type 'i1'.
+  Type 'C2' is not assignable to type 'i1'.
+    Property 'name' is private in type 'C2' but not in type 'i1'.
 tests/cases/compiler/interfaceImplementation8.ts(22,7): error TS2420: Class 'C6' incorrectly implements interface 'i1'.
-  Property 'name' is private in type 'C6' but not in type 'i1'.
+  Type 'C3' is not assignable to type 'i1'.
+    Property 'name' is private in type 'C3' but not in type 'i1'.
 
 
 ==== tests/cases/compiler/interfaceImplementation8.ts (3 errors) ====
@@ -33,11 +35,13 @@ tests/cases/compiler/interfaceImplementation8.ts(22,7): error TS2420: Class 'C6'
     class C5 extends C2 implements i1{ }
           ~~
 !!! error TS2420: Class 'C5' incorrectly implements interface 'i1'.
-!!! error TS2420:   Property 'name' is private in type 'C5' but not in type 'i1'.
+!!! error TS2420:   Type 'C2' is not assignable to type 'i1'.
+!!! error TS2420:     Property 'name' is private in type 'C2' but not in type 'i1'.
     class C6 extends C3 implements i1{ }
           ~~
 !!! error TS2420: Class 'C6' incorrectly implements interface 'i1'.
-!!! error TS2420:   Property 'name' is private in type 'C6' but not in type 'i1'.
+!!! error TS2420:   Type 'C3' is not assignable to type 'i1'.
+!!! error TS2420:     Property 'name' is private in type 'C3' but not in type 'i1'.
     
     /*
         2
diff --git a/tests/baselines/reference/privateNamesUnique-4.errors.txt b/tests/baselines/reference/privateNamesUnique-4.errors.txt
index 889ec0b6a8b5e..a35e70c6ed933 100644
--- a/tests/baselines/reference/privateNamesUnique-4.errors.txt
+++ b/tests/baselines/reference/privateNamesUnique-4.errors.txt
@@ -1,4 +1,5 @@
-tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts(6,7): error TS2741: Property '#something' is missing in type 'A2' but required in type 'C'.
+tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts(6,7): error TS2322: Type 'A2' is not assignable to type 'C'.
+  Property '#something' is missing in type 'A1' but required in type 'C'.
 
 
 ==== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts (1 errors) ====
@@ -9,6 +10,7 @@ tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts(6,7
     class C { #something: number }
     const c: C = a;
           ~
-!!! error TS2741: Property '#something' is missing in type 'A2' but required in type 'C'.
+!!! error TS2322: Type 'A2' is not assignable to type 'C'.
+!!! error TS2322:   Property '#something' is missing in type 'A1' but required in type 'C'.
 !!! related TS2728 tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts:5:11: '#something' is declared here.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/privateNamesUnique-5.errors.txt b/tests/baselines/reference/privateNamesUnique-5.errors.txt
index 31a6d20b99c05..3c8d356439ce2 100644
--- a/tests/baselines/reference/privateNamesUnique-5.errors.txt
+++ b/tests/baselines/reference/privateNamesUnique-5.errors.txt
@@ -1,5 +1,6 @@
 tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts(12,7): error TS2322: Type 'B' is not assignable to type 'A2'.
-  Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type '(anonymous)'.
+  Type 'B' is not assignable to type 'A'.
+    Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type 'A'.
 
 
 ==== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts (1 errors) ====
@@ -17,5 +18,6 @@ tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts(12,
     const b: A2 = new B();
           ~
 !!! error TS2322: Type 'B' is not assignable to type 'A2'.
-!!! error TS2322:   Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type '(anonymous)'.
+!!! error TS2322:   Type 'B' is not assignable to type 'A'.
+!!! error TS2322:     Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type 'A'.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/recursiveComplicatedClasses.types b/tests/baselines/reference/recursiveComplicatedClasses.types
index cf71fde6aab17..8b5c509545cf3 100644
--- a/tests/baselines/reference/recursiveComplicatedClasses.types
+++ b/tests/baselines/reference/recursiveComplicatedClasses.types
@@ -22,7 +22,7 @@ class Symbol {
 >bound : boolean
 
     public visible() {
->visible : () => any
+>visible : () => boolean
 
         var b: TypeSymbol;
 >b : TypeSymbol
diff --git a/tests/baselines/reference/tsxStatelessFunctionComponentOverload4.errors.txt b/tests/baselines/reference/tsxStatelessFunctionComponentOverload4.errors.txt
index 2513a3ba14c1c..b68f9abcfa023 100644
--- a/tests/baselines/reference/tsxStatelessFunctionComponentOverload4.errors.txt
+++ b/tests/baselines/reference/tsxStatelessFunctionComponentOverload4.errors.txt
@@ -64,6 +64,7 @@ tests/cases/conformance/jsx/file.tsx(35,12): error TS2769: No overload matches t
       Property 'children' does not exist on type 'IntrinsicAttributes & { y1?: string; y2?: number; }'.
   Overload 2 of 3, '(a: { y1?: string; y2?: number; children: Element; }): Element', gave the following error.
     Type 'string' is not assignable to type 'Element'.
+      Type 'string' is not assignable to type 'ReactElement<any>'.
   Overload 3 of 3, '(a: { y1: boolean; y2?: number; y3: boolean; }): Element', gave the following error.
     Type 'string' is not assignable to type 'boolean'.
 tests/cases/conformance/jsx/file.tsx(36,12): error TS2769: No overload matches this call.
@@ -197,6 +198,7 @@ tests/cases/conformance/jsx/file.tsx(36,12): error TS2769: No overload matches t
 !!! error TS2769:       Property 'children' does not exist on type 'IntrinsicAttributes & { y1?: string; y2?: number; }'.
 !!! error TS2769:   Overload 2 of 3, '(a: { y1?: string; y2?: number; children: Element; }): Element', gave the following error.
 !!! error TS2769:     Type 'string' is not assignable to type 'Element'.
+!!! error TS2769:       Type 'string' is not assignable to type 'ReactElement<any>'.
 !!! error TS2769:   Overload 3 of 3, '(a: { y1: boolean; y2?: number; y3: boolean; }): Element', gave the following error.
 !!! error TS2769:     Type 'string' is not assignable to type 'boolean'.
 !!! related TS6500 tests/cases/conformance/jsx/file.tsx:29:64: The expected type comes from property 'children' which is declared here on type 'IntrinsicAttributes & { y1?: string; y2?: number; children: Element; }'

From bfcaba49e0c0e8974645890701ad63fbcfe7d436 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wwigham@gmail.com>
Date: Wed, 14 Apr 2021 14:19:21 -0700
Subject: [PATCH 4/6] Cache results, feed through via getNormalizedType to
 remove error intermediates

---
 src/compiler/checker.ts                       | 43 ++++++++-----------
 src/compiler/types.ts                         |  2 +
 .../reference/arrayLiterals3.errors.txt       | 10 ++---
 ...tWithObjectMembersAccessibility.errors.txt | 12 ------
 .../checkJsxChildrenProperty5.errors.txt      |  6 +--
 .../checkJsxChildrenProperty7.errors.txt      |  2 -
 .../classImplementsClass4.errors.txt          |  6 +--
 .../classImplementsClass5.errors.txt          | 12 ++----
 ...ertyIsRelatableToTargetProperty.errors.txt |  6 +--
 ...aceExtendingClassWithProtecteds.errors.txt |  6 +--
 .../reference/inheritance1.errors.txt         | 14 ++----
 ...andParentPrivateMemberCollision.errors.txt |  6 +--
 ...MemberCollisionWithPublicMember.errors.txt |  6 +--
 ...emberCollisionWithPrivateMember.errors.txt |  6 +--
 .../interfaceImplementation8.errors.txt       | 12 ++----
 .../reference/privateNamesUnique-4.errors.txt |  6 +--
 .../reference/privateNamesUnique-5.errors.txt |  6 +--
 ...elessFunctionComponentOverload4.errors.txt |  2 -
 18 files changed, 54 insertions(+), 109 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 5b949b8b6823d..89657a0df9afc 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -17140,12 +17140,12 @@ namespace ts {
 
         function getNormalizedType(type: Type, writing: boolean): Type {
             while (true) {
-                const t = isFreshLiteralType(type) ? (<FreshableType>type).regularType :
+                const t = getSingleBaseForNonAugmentingSubtypeOrType(isFreshLiteralType(type) ? (<FreshableType>type).regularType :
                     getObjectFlags(type) & ObjectFlags.Reference && (<TypeReference>type).node ? createTypeReference((<TypeReference>type).target, getTypeArguments(<TypeReference>type)) :
                     type.flags & TypeFlags.UnionOrIntersection ? getReducedType(type) :
                     type.flags & TypeFlags.Substitution ? writing ? (<SubstitutionType>type).baseType : (<SubstitutionType>type).substitute :
                     type.flags & TypeFlags.Simplifiable ? getSimplifiedType(type, writing) :
-                    type;
+                    type);
                 if (t === type) break;
                 type = t;
             }
@@ -17647,8 +17647,10 @@ namespace ts {
 
                 function reportErrorResults(source: Type, target: Type, result: Ternary, isComparingJsxAttributes: boolean) {
                     if (!result && reportErrors) {
-                        source = originalSource.aliasSymbol ? originalSource : source;
-                        target = originalTarget.aliasSymbol ? originalTarget : target;
+                        const sourceHasBase = getSingleBaseForNonAugmentingSubtypeOrType(originalSource) !== originalSource;
+                        const targetHasBase = getSingleBaseForNonAugmentingSubtypeOrType(originalTarget) !== originalTarget;
+                        source = (originalSource.aliasSymbol || sourceHasBase) ? originalSource : source;
+                        target = (originalTarget.aliasSymbol || targetHasBase) ? originalTarget : target;
                         let maybeSuppress = overrideNextErrorInfo > 0;
                         if (maybeSuppress) {
                             overrideNextErrorInfo--;
@@ -18219,22 +18221,6 @@ namespace ts {
                     return result;
                 }
 
-                let sourceBase = getSingleBaseForNonAugmentingSubtype(source);
-                if (sourceBase) {
-                    if (getObjectFlags(target) & ObjectFlags.Reference && length(getTypeArguments((target as TypeReference))) > length((target as TypeReference).target.typeParameters)) {
-                        sourceBase = getTypeWithThisArgument(sourceBase, last(getTypeArguments(source as TypeReference)));
-                    }
-                    return isRelatedTo(sourceBase, target, reportErrors);
-                }
-
-                let targetBase = getSingleBaseForNonAugmentingSubtype(target);
-                if (targetBase) {
-                    if (getObjectFlags(source) & ObjectFlags.Reference && length(getTypeArguments((source as TypeReference))) > length((source as TypeReference).target.typeParameters)) {
-                        targetBase = getTypeWithThisArgument(targetBase, last(getTypeArguments(target as TypeReference)));
-                    }
-                    return isRelatedTo(source, targetBase, reportErrors);
-                }
-
                 if (target.flags & TypeFlags.TypeParameter) {
                     // A source type { [P in Q]: X } is related to a target type T if keyof T is related to Q and X is related to T[Q].
                     if (getObjectFlags(source) & ObjectFlags.Mapped && !(<MappedType>source).declaration.nameType && isRelatedTo(getIndexType(target), getConstraintTypeFromMappedType(<MappedType>source))) {
@@ -19917,19 +19903,26 @@ namespace ts {
             return isArrayType(type) || !(type.flags & TypeFlags.Nullable) && isTypeAssignableTo(type, anyReadonlyArrayType);
         }
 
-        function getSingleBaseForNonAugmentingSubtype(type: Type) {
+        function getSingleBaseForNonAugmentingSubtypeOrType(type: Type) {
             if (!(getObjectFlags(type) & ObjectFlags.Reference) || !(getObjectFlags((type as TypeReference).target) & ObjectFlags.ClassOrInterface)) {
-                return undefined;
+                return type;
+            }
+            if ((type as TypeReference).cachedEquivalentBaseTypeOrSelf) {
+                return (type as TypeReference).cachedEquivalentBaseTypeOrSelf!;
             }
             const target = (type as TypeReference).target as InterfaceType;
             const bases = getBaseTypes(target);
             if (bases.length !== 1) {
-                return undefined;
+                return (type as TypeReference).cachedEquivalentBaseTypeOrSelf = type;
             }
             if (getMembersOfSymbol(type.symbol).size) {
-                return undefined; // If the interface has any members, they may subtype members in the base, so we should do a full structural comparison
+                return (type as TypeReference).cachedEquivalentBaseTypeOrSelf = type; // If the interface has any members, they may subtype members in the base, so we should do a full structural comparison
+            }
+            let instantiatedBase = !length(target.typeParameters) ? bases[0] : instantiateType(bases[0], createTypeMapper(target.typeParameters!, getTypeArguments(type as TypeReference).slice(0, target.typeParameters!.length)));
+            if (length(getTypeArguments(type as TypeReference)) > length(target.typeParameters)) {
+                instantiatedBase = getTypeWithThisArgument(instantiatedBase, last(getTypeArguments(type as TypeReference)));
             }
-            return !length(target.typeParameters) ? bases[0] : instantiateType(bases[0], createTypeMapper(target.typeParameters!, getTypeArguments(type as TypeReference).slice(0, target.typeParameters!.length)));
+            return (type as TypeReference).cachedEquivalentBaseTypeOrSelf = instantiatedBase;
         }
 
         function isEmptyArrayLiteralType(type: Type): boolean {
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index bea06cb6f7a4e..6b0753b7c4a20 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -5269,6 +5269,8 @@ namespace ts {
         resolvedTypeArguments?: readonly Type[];  // Resolved type reference type arguments
         /* @internal */
         literalType?: TypeReference;  // Clone of type with ObjectFlags.ArrayLiteral set
+        /* @internal */
+        cachedEquivalentBaseTypeOrSelf?: Type; // Only set on references to class or interfaces with a single base type and no augmentations
     }
 
     export interface DeferredTypeReference extends TypeReference {
diff --git a/tests/baselines/reference/arrayLiterals3.errors.txt b/tests/baselines/reference/arrayLiterals3.errors.txt
index 782983eb9884d..3b2d25d17f4ec 100644
--- a/tests/baselines/reference/arrayLiterals3.errors.txt
+++ b/tests/baselines/reference/arrayLiterals3.errors.txt
@@ -8,9 +8,8 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(17,5): error
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(33,5): error TS2322: Type 'number[]' is not assignable to type '[number, number, number]'.
   Target requires 3 element(s) but source may have fewer.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error TS2322: Type '(string | number)[]' is not assignable to type 'myArray'.
-  Type '(string | number)[]' is not assignable to type 'Number[]'.
-    Type 'string | number' is not assignable to type 'Number'.
-      Type 'string' is not assignable to type 'Number'.
+  Type 'string | number' is not assignable to type 'Number'.
+    Type 'string' is not assignable to type 'Number'.
 
 
 ==== tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts (7 errors) ====
@@ -65,7 +64,6 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
     var c2: myArray = [...temp1, ...temp];            // Error cannot assign (number|string)[] to number[]
         ~~
 !!! error TS2322: Type '(string | number)[]' is not assignable to type 'myArray'.
-!!! error TS2322:   Type '(string | number)[]' is not assignable to type 'Number[]'.
-!!! error TS2322:     Type 'string | number' is not assignable to type 'Number'.
-!!! error TS2322:       Type 'string' is not assignable to type 'Number'.
+!!! error TS2322:   Type 'string | number' is not assignable to type 'Number'.
+!!! error TS2322:     Type 'string' is not assignable to type 'Number'.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/assignmentCompatWithObjectMembersAccessibility.errors.txt b/tests/baselines/reference/assignmentCompatWithObjectMembersAccessibility.errors.txt
index 93774cefaa52c..6ca6b5e21e0ea 100644
--- a/tests/baselines/reference/assignmentCompatWithObjectMembersAccessibility.errors.txt
+++ b/tests/baselines/reference/assignmentCompatWithObjectMembersAccessibility.errors.txt
@@ -17,7 +17,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(81,5): error TS2322: Type 'Base' is not assignable to type '{ foo: string; }'.
   Property 'foo' is private in type 'Base' but not in type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(82,5): error TS2322: Type 'I' is not assignable to type '{ foo: string; }'.
-  Type 'Base' is not assignable to type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(84,5): error TS2322: Type 'E' is not assignable to type '{ foo: string; }'.
   Property 'foo' is private in type 'E' but not in type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(86,5): error TS2322: Type '{ foo: string; }' is not assignable to type 'Base'.
@@ -27,15 +26,11 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(89,5): error TS2322: Type 'E' is not assignable to type 'Base'.
   Types have separate declarations of a private property 'foo'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(92,5): error TS2322: Type '{ foo: string; }' is not assignable to type 'I'.
-  Type '{ foo: string; }' is not assignable to type 'Base'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(94,5): error TS2322: Type 'D' is not assignable to type 'I'.
-  Type 'D' is not assignable to type 'Base'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(95,5): error TS2322: Type 'E' is not assignable to type 'I'.
-  Type 'E' is not assignable to type 'Base'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(99,5): error TS2322: Type 'Base' is not assignable to type 'D'.
   Property 'foo' is private in type 'Base' but not in type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(100,5): error TS2322: Type 'I' is not assignable to type 'D'.
-  Type 'Base' is not assignable to type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(101,5): error TS2322: Type 'E' is not assignable to type 'D'.
   Property 'foo' is private in type 'E' but not in type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(103,5): error TS2322: Type '{ foo: string; }' is not assignable to type 'E'.
@@ -43,7 +38,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(104,5): error TS2322: Type 'Base' is not assignable to type 'E'.
   Types have separate declarations of a private property 'foo'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(105,5): error TS2322: Type 'I' is not assignable to type 'E'.
-  Type 'Base' is not assignable to type 'E'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(106,5): error TS2322: Type 'D' is not assignable to type 'E'.
   Property 'foo' is private in type 'E' but not in type 'D'.
 
@@ -160,7 +154,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a = i; // error
         ~
 !!! error TS2322: Type 'I' is not assignable to type '{ foo: string; }'.
-!!! error TS2322:   Type 'Base' is not assignable to type '{ foo: string; }'.
         a = d;
         a = e; // error
         ~
@@ -185,16 +178,13 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         i = a; // error
         ~
 !!! error TS2322: Type '{ foo: string; }' is not assignable to type 'I'.
-!!! error TS2322:   Type '{ foo: string; }' is not assignable to type 'Base'.
         i = b;
         i = d; // error
         ~
 !!! error TS2322: Type 'D' is not assignable to type 'I'.
-!!! error TS2322:   Type 'D' is not assignable to type 'Base'.
         i = e; // error
         ~
 !!! error TS2322: Type 'E' is not assignable to type 'I'.
-!!! error TS2322:   Type 'E' is not assignable to type 'Base'.
         i = i;
     
         d = a;
@@ -205,7 +195,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         d = i; // error
         ~
 !!! error TS2322: Type 'I' is not assignable to type 'D'.
-!!! error TS2322:   Type 'Base' is not assignable to type 'D'.
         d = e; // error
         ~
 !!! error TS2322: Type 'E' is not assignable to type 'D'.
@@ -222,7 +211,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         e = i; // errror
         ~
 !!! error TS2322: Type 'I' is not assignable to type 'E'.
-!!! error TS2322:   Type 'Base' is not assignable to type 'E'.
         e = d; // errror
         ~
 !!! error TS2322: Type 'D' is not assignable to type 'E'.
diff --git a/tests/baselines/reference/checkJsxChildrenProperty5.errors.txt b/tests/baselines/reference/checkJsxChildrenProperty5.errors.txt
index 7f351d9aacd43..aad013f4d8544 100644
--- a/tests/baselines/reference/checkJsxChildrenProperty5.errors.txt
+++ b/tests/baselines/reference/checkJsxChildrenProperty5.errors.txt
@@ -1,6 +1,5 @@
 tests/cases/conformance/jsx/file.tsx(20,10): error TS2741: Property 'children' is missing in type '{ a: number; b: string; }' but required in type 'Prop'.
-tests/cases/conformance/jsx/file.tsx(25,9): error TS2322: Type 'Element' is not assignable to type 'Button'.
-  Type 'ReactElement<any>' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
+tests/cases/conformance/jsx/file.tsx(25,9): error TS2740: Type 'ReactElement<any>' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
 tests/cases/conformance/jsx/file.tsx(29,10): error TS2740: Type 'typeof Button' is missing the following properties from type 'Button': render, setState, forceUpdate, props, and 3 more.
 
 
@@ -34,8 +33,7 @@ tests/cases/conformance/jsx/file.tsx(29,10): error TS2740: Type 'typeof Button'
         <Comp a={10} b="hi">
             <Button />
             ~~~~~~~~~~
-!!! error TS2322: Type 'Element' is not assignable to type 'Button'.
-!!! error TS2322:   Type 'ReactElement<any>' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
+!!! error TS2740: Type 'ReactElement<any>' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
 !!! related TS6500 tests/cases/conformance/jsx/file.tsx:6:5: The expected type comes from property 'children' which is declared here on type 'IntrinsicAttributes & Prop'
         </Comp>;
     let k2 =
diff --git a/tests/baselines/reference/checkJsxChildrenProperty7.errors.txt b/tests/baselines/reference/checkJsxChildrenProperty7.errors.txt
index d5d10f11a2e68..0197bc6cd413e 100644
--- a/tests/baselines/reference/checkJsxChildrenProperty7.errors.txt
+++ b/tests/baselines/reference/checkJsxChildrenProperty7.errors.txt
@@ -1,5 +1,4 @@
 tests/cases/conformance/jsx/file.tsx(24,40): error TS2747: 'Comp' components don't accept text as child elements. Text in JSX has the type 'string', but the expected type of 'children' is 'Element | Element[]'.
-  Type 'string' is not assignable to type 'ReactElement<any>'.
 tests/cases/conformance/jsx/file.tsx(26,22): error TS2747: 'Comp' components don't accept text as child elements. Text in JSX has the type 'string', but the expected type of 'children' is 'Element | Element[]'.
 tests/cases/conformance/jsx/file.tsx(27,30): error TS2747: 'Comp' components don't accept text as child elements. Text in JSX has the type 'string', but the expected type of 'children' is 'Element | Element[]'.
 
@@ -31,7 +30,6 @@ tests/cases/conformance/jsx/file.tsx(27,30): error TS2747: 'Comp' components don
     let k1 = <Comp a={10} b="hi"><Button />  <AnotherButton /></Comp>;
                                            ~~
 !!! error TS2747: 'Comp' components don't accept text as child elements. Text in JSX has the type 'string', but the expected type of 'children' is 'Element | Element[]'.
-!!! error TS2747:   Type 'string' is not assignable to type 'ReactElement<any>'.
     let k2 = <Comp a={10} b="hi"><Button />
         <AnotherButton />  </Comp>;
                          ~~
diff --git a/tests/baselines/reference/classImplementsClass4.errors.txt b/tests/baselines/reference/classImplementsClass4.errors.txt
index 60a3c0b0eafbf..59fff468ee670 100644
--- a/tests/baselines/reference/classImplementsClass4.errors.txt
+++ b/tests/baselines/reference/classImplementsClass4.errors.txt
@@ -1,7 +1,6 @@
 tests/cases/compiler/classImplementsClass4.ts(5,7): error TS2720: Class 'C' incorrectly implements class 'A'. Did you mean to extend 'A' and inherit its members as a subclass?
   Property 'x' is missing in type 'C' but required in type 'A'.
-tests/cases/compiler/classImplementsClass4.ts(16,1): error TS2322: Type 'C' is not assignable to type 'C2'.
-  Property 'x' is missing in type 'C' but required in type 'A'.
+tests/cases/compiler/classImplementsClass4.ts(16,1): error TS2741: Property 'x' is missing in type 'C' but required in type 'A'.
 
 
 ==== tests/cases/compiler/classImplementsClass4.ts (2 errors) ====
@@ -26,6 +25,5 @@ tests/cases/compiler/classImplementsClass4.ts(16,1): error TS2322: Type 'C' is n
     c = c2;
     c2 = c;
     ~~
-!!! error TS2322: Type 'C' is not assignable to type 'C2'.
-!!! error TS2322:   Property 'x' is missing in type 'C' but required in type 'A'.
+!!! error TS2741: Property 'x' is missing in type 'C' but required in type 'A'.
 !!! related TS2728 tests/cases/compiler/classImplementsClass4.ts:2:13: 'x' is declared here.
\ No newline at end of file
diff --git a/tests/baselines/reference/classImplementsClass5.errors.txt b/tests/baselines/reference/classImplementsClass5.errors.txt
index 00c789ac6651a..a291da15407bc 100644
--- a/tests/baselines/reference/classImplementsClass5.errors.txt
+++ b/tests/baselines/reference/classImplementsClass5.errors.txt
@@ -1,11 +1,9 @@
 tests/cases/compiler/classImplementsClass5.ts(5,7): error TS2720: Class 'C' incorrectly implements class 'A'. Did you mean to extend 'A' and inherit its members as a subclass?
   Types have separate declarations of a private property 'x'.
 tests/cases/compiler/classImplementsClass5.ts(16,1): error TS2322: Type 'C2' is not assignable to type 'C'.
-  Type 'A' is not assignable to type 'C'.
-    Types have separate declarations of a private property 'x'.
+  Types have separate declarations of a private property 'x'.
 tests/cases/compiler/classImplementsClass5.ts(17,1): error TS2322: Type 'C' is not assignable to type 'C2'.
-  Type 'C' is not assignable to type 'A'.
-    Types have separate declarations of a private property 'x'.
+  Types have separate declarations of a private property 'x'.
 
 
 ==== tests/cases/compiler/classImplementsClass5.ts (3 errors) ====
@@ -30,10 +28,8 @@ tests/cases/compiler/classImplementsClass5.ts(17,1): error TS2322: Type 'C' is n
     c = c2;
     ~
 !!! error TS2322: Type 'C2' is not assignable to type 'C'.
-!!! error TS2322:   Type 'A' is not assignable to type 'C'.
-!!! error TS2322:     Types have separate declarations of a private property 'x'.
+!!! error TS2322:   Types have separate declarations of a private property 'x'.
     c2 = c;
     ~~
 !!! error TS2322: Type 'C' is not assignable to type 'C2'.
-!!! error TS2322:   Type 'C' is not assignable to type 'A'.
-!!! error TS2322:     Types have separate declarations of a private property 'x'.
\ No newline at end of file
+!!! error TS2322:   Types have separate declarations of a private property 'x'.
\ No newline at end of file
diff --git a/tests/baselines/reference/crashInsourcePropertyIsRelatableToTargetProperty.errors.txt b/tests/baselines/reference/crashInsourcePropertyIsRelatableToTargetProperty.errors.txt
index d57411e508c43..40deaf591d8f1 100644
--- a/tests/baselines/reference/crashInsourcePropertyIsRelatableToTargetProperty.errors.txt
+++ b/tests/baselines/reference/crashInsourcePropertyIsRelatableToTargetProperty.errors.txt
@@ -1,5 +1,4 @@
-tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts(9,5): error TS2322: Type '(x: "hi", items: string[]) => typeof foo' is not assignable to type 'D'.
-  Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'C'.
+tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts(9,5): error TS2741: Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'C'.
 
 
 ==== tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts (1 errors) ====
@@ -13,7 +12,6 @@ tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts(9,5): e
     }
     var a: D = foo("hi", []);
         ~
-!!! error TS2322: Type '(x: "hi", items: string[]) => typeof foo' is not assignable to type 'D'.
-!!! error TS2322:   Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'C'.
+!!! error TS2741: Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'C'.
 !!! related TS2728 tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts:2:13: 'x' is declared here.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/implementingAnInterfaceExtendingClassWithProtecteds.errors.txt b/tests/baselines/reference/implementingAnInterfaceExtendingClassWithProtecteds.errors.txt
index 215af9421d584..104bdb5c4d1ce 100644
--- a/tests/baselines/reference/implementingAnInterfaceExtendingClassWithProtecteds.errors.txt
+++ b/tests/baselines/reference/implementingAnInterfaceExtendingClassWithProtecteds.errors.txt
@@ -7,8 +7,7 @@ tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInte
 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts(21,7): error TS2420: Class 'Bar4' incorrectly implements interface 'I'.
   Property 'x' is protected but type 'Bar4' is not a class derived from 'Foo'.
 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts(26,7): error TS2420: Class 'Bar5' incorrectly implements interface 'I'.
-  Type 'Foo' is not assignable to type 'I'.
-    Property 'y' is missing in type 'Foo' but required in type 'I'.
+  Property 'y' is missing in type 'Foo' but required in type 'I'.
 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts(29,7): error TS2420: Class 'Bar6' incorrectly implements interface 'I'.
   Property 'y' is protected in type 'Bar6' but public in type 'I'.
 
@@ -55,8 +54,7 @@ tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInte
     class Bar5 extends Foo implements I { // error
           ~~~~
 !!! error TS2420: Class 'Bar5' incorrectly implements interface 'I'.
-!!! error TS2420:   Type 'Foo' is not assignable to type 'I'.
-!!! error TS2420:     Property 'y' is missing in type 'Foo' but required in type 'I'.
+!!! error TS2420:   Property 'y' is missing in type 'Foo' but required in type 'I'.
 !!! related TS2728 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts:6:5: 'y' is declared here.
     }
     
diff --git a/tests/baselines/reference/inheritance1.errors.txt b/tests/baselines/reference/inheritance1.errors.txt
index f7223fdfd4adc..05e85c4834529 100644
--- a/tests/baselines/reference/inheritance1.errors.txt
+++ b/tests/baselines/reference/inheritance1.errors.txt
@@ -1,14 +1,11 @@
 tests/cases/compiler/inheritance1.ts(14,7): error TS2420: Class 'ImageBase' incorrectly implements interface 'SelectableControl'.
-  Type 'Control' is not assignable to type 'SelectableControl'.
-    Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
+  Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
 tests/cases/compiler/inheritance1.ts(18,7): error TS2420: Class 'Locations' incorrectly implements interface 'SelectableControl'.
   Property 'state' is missing in type 'Locations' but required in type 'SelectableControl'.
 tests/cases/compiler/inheritance1.ts(31,1): error TS2741: Property 'select' is missing in type 'Control' but required in type 'Button'.
 tests/cases/compiler/inheritance1.ts(37,1): error TS2741: Property 'select' is missing in type 'Control' but required in type 'TextBox'.
-tests/cases/compiler/inheritance1.ts(40,1): error TS2322: Type 'ImageBase' is not assignable to type 'SelectableControl'.
-  Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
+tests/cases/compiler/inheritance1.ts(40,1): error TS2741: Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
 tests/cases/compiler/inheritance1.ts(46,1): error TS2322: Type 'Image1' is not assignable to type 'SelectableControl'.
-  Type 'Control' is not assignable to type 'SelectableControl'.
 tests/cases/compiler/inheritance1.ts(52,1): error TS2741: Property 'state' is missing in type 'Locations' but required in type 'SelectableControl'.
 tests/cases/compiler/inheritance1.ts(53,1): error TS2741: Property 'state' is missing in type 'Locations' but required in type 'Control'.
 tests/cases/compiler/inheritance1.ts(55,1): error TS2741: Property 'select' is missing in type 'Control' but required in type 'Locations'.
@@ -34,8 +31,7 @@ tests/cases/compiler/inheritance1.ts(61,1): error TS2741: Property 'select' is m
     class ImageBase extends Control implements SelectableControl{
           ~~~~~~~~~
 !!! error TS2420: Class 'ImageBase' incorrectly implements interface 'SelectableControl'.
-!!! error TS2420:   Type 'Control' is not assignable to type 'SelectableControl'.
-!!! error TS2420:     Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
+!!! error TS2420:   Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
 !!! related TS2728 tests/cases/compiler/inheritance1.ts:5:5: 'select' is declared here.
     }
     class Image1 extends Control {
@@ -74,8 +70,7 @@ tests/cases/compiler/inheritance1.ts(61,1): error TS2741: Property 'select' is m
     var i: ImageBase;
     sc = i;
     ~~
-!!! error TS2322: Type 'ImageBase' is not assignable to type 'SelectableControl'.
-!!! error TS2322:   Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
+!!! error TS2741: Property 'select' is missing in type 'Control' but required in type 'SelectableControl'.
 !!! related TS2728 tests/cases/compiler/inheritance1.ts:5:5: 'select' is declared here.
     c = i;
     i = sc;
@@ -85,7 +80,6 @@ tests/cases/compiler/inheritance1.ts(61,1): error TS2741: Property 'select' is m
     sc = i1;
     ~~
 !!! error TS2322: Type 'Image1' is not assignable to type 'SelectableControl'.
-!!! error TS2322:   Type 'Control' is not assignable to type 'SelectableControl'.
     c = i1;
     i1 = sc;
     i1 = c;
diff --git a/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollision.errors.txt b/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollision.errors.txt
index c8d18fa915afe..84a04107008f7 100644
--- a/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollision.errors.txt
+++ b/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollision.errors.txt
@@ -1,6 +1,5 @@
 tests/cases/compiler/inheritanceGrandParentPrivateMemberCollision.ts(7,7): error TS2415: Class 'C' incorrectly extends base class 'B'.
-  Type 'C' is not assignable to type 'A'.
-    Types have separate declarations of a private property 'myMethod'.
+  Types have separate declarations of a private property 'myMethod'.
 
 
 ==== tests/cases/compiler/inheritanceGrandParentPrivateMemberCollision.ts (1 errors) ====
@@ -13,8 +12,7 @@ tests/cases/compiler/inheritanceGrandParentPrivateMemberCollision.ts(7,7): error
     class C extends B {
           ~
 !!! error TS2415: Class 'C' incorrectly extends base class 'B'.
-!!! error TS2415:   Type 'C' is not assignable to type 'A'.
-!!! error TS2415:     Types have separate declarations of a private property 'myMethod'.
+!!! error TS2415:   Types have separate declarations of a private property 'myMethod'.
         private myMethod() { }
     }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.errors.txt b/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.errors.txt
index 3febf1888744d..f621ed4cfee2d 100644
--- a/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.errors.txt
+++ b/tests/baselines/reference/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.errors.txt
@@ -1,6 +1,5 @@
 tests/cases/compiler/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.ts(7,7): error TS2415: Class 'C' incorrectly extends base class 'B'.
-  Type 'C' is not assignable to type 'A'.
-    Property 'myMethod' is private in type 'A' but not in type 'C'.
+  Property 'myMethod' is private in type 'A' but not in type 'C'.
 
 
 ==== tests/cases/compiler/inheritanceGrandParentPrivateMemberCollisionWithPublicMember.ts (1 errors) ====
@@ -13,8 +12,7 @@ tests/cases/compiler/inheritanceGrandParentPrivateMemberCollisionWithPublicMembe
     class C extends B {
           ~
 !!! error TS2415: Class 'C' incorrectly extends base class 'B'.
-!!! error TS2415:   Type 'C' is not assignable to type 'A'.
-!!! error TS2415:     Property 'myMethod' is private in type 'A' but not in type 'C'.
+!!! error TS2415:   Property 'myMethod' is private in type 'A' but not in type 'C'.
         public myMethod() { }
     }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.errors.txt b/tests/baselines/reference/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.errors.txt
index 561f83bf6d363..2218a73a3341a 100644
--- a/tests/baselines/reference/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.errors.txt
+++ b/tests/baselines/reference/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.errors.txt
@@ -1,6 +1,5 @@
 tests/cases/compiler/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.ts(7,7): error TS2415: Class 'C' incorrectly extends base class 'B'.
-  Type 'C' is not assignable to type 'A'.
-    Property 'myMethod' is private in type 'C' but not in type 'A'.
+  Property 'myMethod' is private in type 'C' but not in type 'A'.
 
 
 ==== tests/cases/compiler/inheritanceGrandParentPublicMemberCollisionWithPrivateMember.ts (1 errors) ====
@@ -13,8 +12,7 @@ tests/cases/compiler/inheritanceGrandParentPublicMemberCollisionWithPrivateMembe
     class C extends B {
           ~
 !!! error TS2415: Class 'C' incorrectly extends base class 'B'.
-!!! error TS2415:   Type 'C' is not assignable to type 'A'.
-!!! error TS2415:     Property 'myMethod' is private in type 'C' but not in type 'A'.
+!!! error TS2415:   Property 'myMethod' is private in type 'C' but not in type 'A'.
         private myMethod() { }
     }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/interfaceImplementation8.errors.txt b/tests/baselines/reference/interfaceImplementation8.errors.txt
index 81898f3aacc73..68cb613c211af 100644
--- a/tests/baselines/reference/interfaceImplementation8.errors.txt
+++ b/tests/baselines/reference/interfaceImplementation8.errors.txt
@@ -1,11 +1,9 @@
 tests/cases/compiler/interfaceImplementation8.ts(12,7): error TS2420: Class 'C2' incorrectly implements interface 'i1'.
   Property 'name' is private in type 'C2' but not in type 'i1'.
 tests/cases/compiler/interfaceImplementation8.ts(21,7): error TS2420: Class 'C5' incorrectly implements interface 'i1'.
-  Type 'C2' is not assignable to type 'i1'.
-    Property 'name' is private in type 'C2' but not in type 'i1'.
+  Property 'name' is private in type 'C2' but not in type 'i1'.
 tests/cases/compiler/interfaceImplementation8.ts(22,7): error TS2420: Class 'C6' incorrectly implements interface 'i1'.
-  Type 'C3' is not assignable to type 'i1'.
-    Property 'name' is private in type 'C3' but not in type 'i1'.
+  Property 'name' is private in type 'C3' but not in type 'i1'.
 
 
 ==== tests/cases/compiler/interfaceImplementation8.ts (3 errors) ====
@@ -35,13 +33,11 @@ tests/cases/compiler/interfaceImplementation8.ts(22,7): error TS2420: Class 'C6'
     class C5 extends C2 implements i1{ }
           ~~
 !!! error TS2420: Class 'C5' incorrectly implements interface 'i1'.
-!!! error TS2420:   Type 'C2' is not assignable to type 'i1'.
-!!! error TS2420:     Property 'name' is private in type 'C2' but not in type 'i1'.
+!!! error TS2420:   Property 'name' is private in type 'C2' but not in type 'i1'.
     class C6 extends C3 implements i1{ }
           ~~
 !!! error TS2420: Class 'C6' incorrectly implements interface 'i1'.
-!!! error TS2420:   Type 'C3' is not assignable to type 'i1'.
-!!! error TS2420:     Property 'name' is private in type 'C3' but not in type 'i1'.
+!!! error TS2420:   Property 'name' is private in type 'C3' but not in type 'i1'.
     
     /*
         2
diff --git a/tests/baselines/reference/privateNamesUnique-4.errors.txt b/tests/baselines/reference/privateNamesUnique-4.errors.txt
index a35e70c6ed933..02e0e79b846cd 100644
--- a/tests/baselines/reference/privateNamesUnique-4.errors.txt
+++ b/tests/baselines/reference/privateNamesUnique-4.errors.txt
@@ -1,5 +1,4 @@
-tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts(6,7): error TS2322: Type 'A2' is not assignable to type 'C'.
-  Property '#something' is missing in type 'A1' but required in type 'C'.
+tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts(6,7): error TS2741: Property '#something' is missing in type 'A1' but required in type 'C'.
 
 
 ==== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts (1 errors) ====
@@ -10,7 +9,6 @@ tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts(6,7
     class C { #something: number }
     const c: C = a;
           ~
-!!! error TS2322: Type 'A2' is not assignable to type 'C'.
-!!! error TS2322:   Property '#something' is missing in type 'A1' but required in type 'C'.
+!!! error TS2741: Property '#something' is missing in type 'A1' but required in type 'C'.
 !!! related TS2728 tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts:5:11: '#something' is declared here.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/privateNamesUnique-5.errors.txt b/tests/baselines/reference/privateNamesUnique-5.errors.txt
index 3c8d356439ce2..4ec5413f879c4 100644
--- a/tests/baselines/reference/privateNamesUnique-5.errors.txt
+++ b/tests/baselines/reference/privateNamesUnique-5.errors.txt
@@ -1,6 +1,5 @@
 tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts(12,7): error TS2322: Type 'B' is not assignable to type 'A2'.
-  Type 'B' is not assignable to type 'A'.
-    Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type 'A'.
+  Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type 'A'.
 
 
 ==== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts (1 errors) ====
@@ -18,6 +17,5 @@ tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts(12,
     const b: A2 = new B();
           ~
 !!! error TS2322: Type 'B' is not assignable to type 'A2'.
-!!! error TS2322:   Type 'B' is not assignable to type 'A'.
-!!! error TS2322:     Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type 'A'.
+!!! error TS2322:   Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type 'A'.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/tsxStatelessFunctionComponentOverload4.errors.txt b/tests/baselines/reference/tsxStatelessFunctionComponentOverload4.errors.txt
index b68f9abcfa023..2513a3ba14c1c 100644
--- a/tests/baselines/reference/tsxStatelessFunctionComponentOverload4.errors.txt
+++ b/tests/baselines/reference/tsxStatelessFunctionComponentOverload4.errors.txt
@@ -64,7 +64,6 @@ tests/cases/conformance/jsx/file.tsx(35,12): error TS2769: No overload matches t
       Property 'children' does not exist on type 'IntrinsicAttributes & { y1?: string; y2?: number; }'.
   Overload 2 of 3, '(a: { y1?: string; y2?: number; children: Element; }): Element', gave the following error.
     Type 'string' is not assignable to type 'Element'.
-      Type 'string' is not assignable to type 'ReactElement<any>'.
   Overload 3 of 3, '(a: { y1: boolean; y2?: number; y3: boolean; }): Element', gave the following error.
     Type 'string' is not assignable to type 'boolean'.
 tests/cases/conformance/jsx/file.tsx(36,12): error TS2769: No overload matches this call.
@@ -198,7 +197,6 @@ tests/cases/conformance/jsx/file.tsx(36,12): error TS2769: No overload matches t
 !!! error TS2769:       Property 'children' does not exist on type 'IntrinsicAttributes & { y1?: string; y2?: number; }'.
 !!! error TS2769:   Overload 2 of 3, '(a: { y1?: string; y2?: number; children: Element; }): Element', gave the following error.
 !!! error TS2769:     Type 'string' is not assignable to type 'Element'.
-!!! error TS2769:       Type 'string' is not assignable to type 'ReactElement<any>'.
 !!! error TS2769:   Overload 3 of 3, '(a: { y1: boolean; y2?: number; y3: boolean; }): Element', gave the following error.
 !!! error TS2769:     Type 'string' is not assignable to type 'boolean'.
 !!! related TS6500 tests/cases/conformance/jsx/file.tsx:29:64: The expected type comes from property 'children' which is declared here on type 'IntrinsicAttributes & { y1?: string; y2?: number; children: Element; }'

From f45c2e263507af67deaee84ec18d43172f710782 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wwigham@gmail.com>
Date: Mon, 19 Apr 2021 17:31:38 -0700
Subject: [PATCH 5/6] Use newly freed up object flags to limit member setting,
 fix crash with those object flags

---
 src/compiler/checker.ts | 27 +++++++++++++++------------
 src/compiler/types.ts   |  8 +++++++-
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index d24f42a64daa2..98aa2907ca928 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11857,7 +11857,7 @@ namespace ts {
         }
 
         function elaborateNeverIntersection(errorInfo: DiagnosticMessageChain | undefined, type: Type) {
-            if (getObjectFlags(type) & ObjectFlags.IsNeverIntersection) {
+            if (type.flags & TypeFlags.Intersection && getObjectFlags(type) & ObjectFlags.IsNeverIntersection) {
                 const neverProp = find(getPropertiesOfUnionOrIntersectionType(<IntersectionType>type), isDiscriminantWithNeverType);
                 if (neverProp) {
                     return chainDiagnosticMessages(errorInfo, Diagnostics.The_intersection_0_was_reduced_to_never_because_property_1_has_conflicting_types_in_some_constituents,
@@ -17178,12 +17178,13 @@ namespace ts {
 
         function getNormalizedType(type: Type, writing: boolean): Type {
             while (true) {
-                const t = getSingleBaseForNonAugmentingSubtypeOrType(isFreshLiteralType(type) ? (<FreshableType>type).regularType :
+                let t = isFreshLiteralType(type) ? (<FreshableType>type).regularType :
                     getObjectFlags(type) & ObjectFlags.Reference && (<TypeReference>type).node ? createTypeReference((<TypeReference>type).target, getTypeArguments(<TypeReference>type)) :
                     type.flags & TypeFlags.UnionOrIntersection ? getReducedType(type) :
                     type.flags & TypeFlags.Substitution ? writing ? (<SubstitutionType>type).baseType : (<SubstitutionType>type).substitute :
                     type.flags & TypeFlags.Simplifiable ? getSimplifiedType(type, writing) :
-                    type);
+                    type;
+                t = getSingleBaseForNonAugmentingSubtype(t) || t;
                 if (t === type) break;
                 type = t;
             }
@@ -17685,8 +17686,8 @@ namespace ts {
 
                 function reportErrorResults(source: Type, target: Type, result: Ternary, isComparingJsxAttributes: boolean) {
                     if (!result && reportErrors) {
-                        const sourceHasBase = getSingleBaseForNonAugmentingSubtypeOrType(originalSource) !== originalSource;
-                        const targetHasBase = getSingleBaseForNonAugmentingSubtypeOrType(originalTarget) !== originalTarget;
+                        const sourceHasBase = !!getSingleBaseForNonAugmentingSubtype(originalSource);
+                        const targetHasBase = !!getSingleBaseForNonAugmentingSubtype(originalTarget);
                         source = (originalSource.aliasSymbol || sourceHasBase) ? originalSource : source;
                         target = (originalTarget.aliasSymbol || targetHasBase) ? originalTarget : target;
                         let maybeSuppress = overrideNextErrorInfo > 0;
@@ -19941,26 +19942,28 @@ namespace ts {
             return isArrayType(type) || !(type.flags & TypeFlags.Nullable) && isTypeAssignableTo(type, anyReadonlyArrayType);
         }
 
-        function getSingleBaseForNonAugmentingSubtypeOrType(type: Type) {
+        function getSingleBaseForNonAugmentingSubtype(type: Type) {
             if (!(getObjectFlags(type) & ObjectFlags.Reference) || !(getObjectFlags((type as TypeReference).target) & ObjectFlags.ClassOrInterface)) {
-                return type;
+                return undefined;
             }
-            if ((type as TypeReference).cachedEquivalentBaseTypeOrSelf) {
-                return (type as TypeReference).cachedEquivalentBaseTypeOrSelf!;
+            if (getObjectFlags(type) & ObjectFlags.IdenticalBaseTypeCalculated) {
+                return getObjectFlags(type) & ObjectFlags.IdenticalBaseTypeExists ? (type as TypeReference).cachedEquivalentBaseType : undefined;
             }
+            (type as TypeReference).objectFlags |= ObjectFlags.IdenticalBaseTypeCalculated;
             const target = (type as TypeReference).target as InterfaceType;
             const bases = getBaseTypes(target);
             if (bases.length !== 1) {
-                return (type as TypeReference).cachedEquivalentBaseTypeOrSelf = type;
+                return undefined;
             }
             if (getMembersOfSymbol(type.symbol).size) {
-                return (type as TypeReference).cachedEquivalentBaseTypeOrSelf = type; // If the interface has any members, they may subtype members in the base, so we should do a full structural comparison
+                return undefined; // If the interface has any members, they may subtype members in the base, so we should do a full structural comparison
             }
             let instantiatedBase = !length(target.typeParameters) ? bases[0] : instantiateType(bases[0], createTypeMapper(target.typeParameters!, getTypeArguments(type as TypeReference).slice(0, target.typeParameters!.length)));
             if (length(getTypeArguments(type as TypeReference)) > length(target.typeParameters)) {
                 instantiatedBase = getTypeWithThisArgument(instantiatedBase, last(getTypeArguments(type as TypeReference)));
             }
-            return (type as TypeReference).cachedEquivalentBaseTypeOrSelf = instantiatedBase;
+            (type as TypeReference).objectFlags |= ObjectFlags.IdenticalBaseTypeExists;
+            return (type as TypeReference).cachedEquivalentBaseType = instantiatedBase;
         }
 
         function isEmptyArrayLiteralType(type: Type): boolean {
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 8f14a7187dd33..d4695ced74c11 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -5219,6 +5219,12 @@ namespace ts {
         IsNeverIntersectionComputed = 1 << 26, // IsNeverLike flag has been computed
         /* @internal */
         IsNeverIntersection = 1 << 27, // Intersection reduces to never
+
+        // Flags that require TypeFlags.Reference
+        /* @internal */
+        IdenticalBaseTypeCalculated = 1 << 26, // has had `getSingleBaseForNonAugmentingSubtype` invoked on it already
+        /* @internal */
+        IdenticalBaseTypeExists = 1 << 27, // has a defined cachedEquivalentBaseType member
     }
 
     /* @internal */
@@ -5281,7 +5287,7 @@ namespace ts {
         /* @internal */
         literalType?: TypeReference;  // Clone of type with ObjectFlags.ArrayLiteral set
         /* @internal */
-        cachedEquivalentBaseTypeOrSelf?: Type; // Only set on references to class or interfaces with a single base type and no augmentations
+        cachedEquivalentBaseType?: Type; // Only set on references to class or interfaces with a single base type and no augmentations
     }
 
     export interface DeferredTypeReference extends TypeReference {

From 0422b9688ef774ab50d3e4a24a232d5f2c0c3a8f Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wwigham@gmail.com>
Date: Tue, 27 Apr 2021 15:00:44 -0700
Subject: [PATCH 6/6] Move flags because there is no TypeFlags.Reference
 :facepalm:

---
 src/compiler/types.ts | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 86d381c51be61..4bded5742c59a 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -5200,6 +5200,11 @@ namespace ts {
         ObjectRestType   = 1 << 23,  // Originates in object rest declaration
         /* @internal */
         IsClassInstanceClone = 1 << 24, // Type is a clone of a class instance type
+        // Flags that require TypeFlags.Object and ObjectFlags.Reference
+        /* @internal */
+        IdenticalBaseTypeCalculated = 1 << 25, // has had `getSingleBaseForNonAugmentingSubtype` invoked on it already
+        /* @internal */
+        IdenticalBaseTypeExists = 1 << 26, // has a defined cachedEquivalentBaseType member
 
         // Flags that require TypeFlags.UnionOrIntersection
         /* @internal */
@@ -5220,12 +5225,6 @@ namespace ts {
         IsNeverIntersectionComputed = 1 << 26, // IsNeverLike flag has been computed
         /* @internal */
         IsNeverIntersection = 1 << 27, // Intersection reduces to never
-
-        // Flags that require TypeFlags.Reference
-        /* @internal */
-        IdenticalBaseTypeCalculated = 1 << 26, // has had `getSingleBaseForNonAugmentingSubtype` invoked on it already
-        /* @internal */
-        IdenticalBaseTypeExists = 1 << 27, // has a defined cachedEquivalentBaseType member
     }
 
     /* @internal */