[release-3.2] Overlappy elaboration on unions

src/compiler/checker.ts

@@ -11921,7 +11921,8 @@ namespace ts {
                         findMatchingDiscriminantType(source, target) ||
                         findMatchingTypeReferenceOrTypeAliasReference(source, target) ||
                         findBestTypeForObjectLiteral(source, target) ||
-                        findBestTypeForInvokable(source, target);
+                        findBestTypeForInvokable(source, target) ||
+                        findMostOverlappyType(source, target);
 
                     isRelatedTo(source, bestMatchingType || targetTypes[targetTypes.length - 1], /*reportErrors*/ true);
                 }
@@ -11961,6 +11962,34 @@ namespace ts {
                 }
             }
 
+            function findMostOverlappyType(source: Type, unionTarget: UnionOrIntersectionType) {
+                let bestMatch: Type | undefined;
+                let matchingCount = 0;
+                for (const target of unionTarget.types) {
+                    const overlap = getIntersectionType([getIndexType(source), getIndexType(target)]);
+                    if (overlap.flags & TypeFlags.Index) {
+                        // perfect overlap of keys
+                        bestMatch = target;
+                        matchingCount = Infinity;
+                    }
+                    else if (overlap.flags & TypeFlags.Union) {
+                        // Some subset overlap if we have only string literals.
+                        // If we have a union of index types, it seems likely that we
+                        // needed to elaborate between two generic mapped types anyway.
+                        const len = length((overlap as UnionType).types);
+                        if (len >= matchingCount) {
+                            bestMatch = target;
+                            matchingCount = len;
+                        }
+                    }
+                    else if (!(overlap.flags & TypeFlags.Never) && 1 >= matchingCount) {
+                        bestMatch = target;
+                        matchingCount = 1;
+                    }
+                }
+                return bestMatch;
+            }
+
             // Keep this up-to-date with the same logic within `getApparentTypeOfContextualType`, since they should behave similarly
             function findMatchingDiscriminantType(source: Type, target: Type) {
                 if (target.flags & TypeFlags.Union) {

tests/baselines/reference/checkJsxChildrenProperty2.errors.txt

@@ -3,19 +3,19 @@ tests/cases/conformance/jsx/file.tsx(17,11): error TS2710: 'children' are specif
 tests/cases/conformance/jsx/file.tsx(31,6): error TS2322: Type '{ children: (Element | ((name: string) => Element))[]; a: number; b: string; }' is not assignable to type 'Prop'.
   Types of property 'children' are incompatible.
     Type '(Element | ((name: string) => Element))[]' is not assignable to type 'string | Element'.
-      Type '(Element | ((name: string) => Element))[]' is missing the following properties from type 'Element': type, props
+      Type '(Element | ((name: string) => Element))[]' is not assignable to type 'string'.
 tests/cases/conformance/jsx/file.tsx(37,6): error TS2322: Type '{ children: (number | Element)[]; a: number; b: string; }' is not assignable to type 'Prop'.
   Types of property 'children' are incompatible.
     Type '(number | Element)[]' is not assignable to type 'string | Element'.
-      Type '(number | Element)[]' is missing the following properties from type 'Element': type, props
+      Type '(number | Element)[]' is not assignable to type 'string'.
 tests/cases/conformance/jsx/file.tsx(43,6): error TS2322: Type '{ children: (string | Element)[]; a: number; b: string; }' is not assignable to type 'Prop'.
   Types of property 'children' are incompatible.
     Type '(string | Element)[]' is not assignable to type 'string | Element'.
-      Type '(string | Element)[]' is missing the following properties from type 'Element': type, props
+      Type '(string | Element)[]' is not assignable to type 'string'.
 tests/cases/conformance/jsx/file.tsx(49,6): error TS2322: Type '{ children: Element[]; a: number; b: string; }' is not assignable to type 'Prop'.
   Types of property 'children' are incompatible.
     Type 'Element[]' is not assignable to type 'string | Element'.
-      Type 'Element[]' is missing the following properties from type 'Element': type, props
+      Type 'Element[]' is not assignable to type 'string'.
 
 
 ==== tests/cases/conformance/jsx/file.tsx (6 errors) ====
@@ -59,7 +59,7 @@ tests/cases/conformance/jsx/file.tsx(49,6): error TS2322: Type '{ children: Elem
 !!! error TS2322: Type '{ children: (Element | ((name: string) => Element))[]; a: number; b: string; }' is not assignable to type 'Prop'.
 !!! error TS2322:   Types of property 'children' are incompatible.
 !!! error TS2322:     Type '(Element | ((name: string) => Element))[]' is not assignable to type 'string | Element'.
-!!! error TS2322:       Type '(Element | ((name: string) => Element))[]' is missing the following properties from type 'Element': type, props
+!!! error TS2322:       Type '(Element | ((name: string) => Element))[]' is not assignable to type 'string'.
             <div> My Div </div>
             {(name: string) => <div> My name {name} </div>}
         </Comp>;
@@ -70,7 +70,7 @@ tests/cases/conformance/jsx/file.tsx(49,6): error TS2322: Type '{ children: Elem
 !!! error TS2322: Type '{ children: (number | Element)[]; a: number; b: string; }' is not assignable to type 'Prop'.
 !!! error TS2322:   Types of property 'children' are incompatible.
 !!! error TS2322:     Type '(number | Element)[]' is not assignable to type 'string | Element'.
-!!! error TS2322:       Type '(number | Element)[]' is missing the following properties from type 'Element': type, props
+!!! error TS2322:       Type '(number | Element)[]' is not assignable to type 'string'.
             <div> My Div </div>
             {1000000}
         </Comp>;
@@ -81,7 +81,7 @@ tests/cases/conformance/jsx/file.tsx(49,6): error TS2322: Type '{ children: Elem
 !!! error TS2322: Type '{ children: (string | Element)[]; a: number; b: string; }' is not assignable to type 'Prop'.
 !!! error TS2322:   Types of property 'children' are incompatible.
 !!! error TS2322:     Type '(string | Element)[]' is not assignable to type 'string | Element'.
-!!! error TS2322:       Type '(string | Element)[]' is missing the following properties from type 'Element': type, props
+!!! error TS2322:       Type '(string | Element)[]' is not assignable to type 'string'.
             <div> My Div </div>
             hi hi hi!
         </Comp>;
@@ -92,7 +92,7 @@ tests/cases/conformance/jsx/file.tsx(49,6): error TS2322: Type '{ children: Elem
 !!! error TS2322: Type '{ children: Element[]; a: number; b: string; }' is not assignable to type 'Prop'.
 !!! error TS2322:   Types of property 'children' are incompatible.
 !!! error TS2322:     Type 'Element[]' is not assignable to type 'string | Element'.
-!!! error TS2322:       Type 'Element[]' is missing the following properties from type 'Element': type, props
+!!! error TS2322:       Type 'Element[]' is not assignable to type 'string'.
             <div> My Div </div>
             <div> My Div </div>
         </Comp>;

tests/baselines/reference/contextualTypeWithUnionTypeObjectLiteral.errors.txt

@@ -9,12 +9,15 @@ tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(
       Type 'string | number' is not assignable to type 'number'.
         Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(21,5): error TS2322: Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; }'.
-  Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: number; }'.
+  Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; }'.
     Types of property 'prop' are incompatible.
-      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 'string'.
+        Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(25,5): error TS2322: Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; anotherP1: number; }'.
-  Property 'anotherP1' is missing in type '{ prop: string | number; anotherP: string; }' but required in type '{ prop: number; anotherP1: number; }'.
+  Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; }'.
+    Types of property 'prop' are incompatible.
+      Type 'string | number' is not assignable to type 'string'.
+        Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(29,5): error TS2322: Type '{ prop: string | number; anotherP: string; anotherP1: number; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; anotherP1: number; }'.
   Type '{ prop: string | number; anotherP: string; anotherP1: number; }' is not assignable to type '{ prop: number; anotherP1: number; }'.
     Types of property 'prop' are incompatible.
@@ -62,18 +65,20 @@ tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts(
     var objStrOrNum6: { prop: string; anotherP: string; } | { prop: number } = {
         ~~~~~~~~~~~~
 !!! error TS2322: Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; }'.
-!!! error TS2322:   Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: number; }'.
+!!! error TS2322:   Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; }'.
 !!! error TS2322:     Types of property 'prop' are incompatible.
-!!! 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 'string'.
+!!! error TS2322:         Type 'number' is not assignable to type 'string'.
         prop: strOrNumber,
         anotherP: str
     };
     var objStrOrNum7: { prop: string; anotherP: string; } | { prop: number; anotherP1: number } = {
         ~~~~~~~~~~~~
 !!! error TS2322: Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; } | { prop: number; anotherP1: number; }'.
-!!! error TS2322:   Property 'anotherP1' is missing in type '{ prop: string | number; anotherP: string; }' but required in type '{ prop: number; anotherP1: number; }'.
-!!! related TS2728 tests/cases/conformance/types/union/contextualTypeWithUnionTypeObjectLiteral.ts:25:73: 'anotherP1' is declared here.
+!!! error TS2322:   Type '{ prop: string | number; anotherP: string; }' is not assignable to type '{ prop: string; anotherP: string; }'.
+!!! error TS2322:     Types of property 'prop' are incompatible.
+!!! error TS2322:       Type 'string | number' is not assignable to type 'string'.
+!!! error TS2322:         Type 'number' is not assignable to type 'string'.
         prop: strOrNumber,
         anotherP: str
     };

tests/baselines/reference/errorsOnUnionsOfOverlappingObjects01.errors.txt

@@ -0,0 +1,56 @@
+tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(18,3): error TS2345: Argument of type '{ a: string; b: string; }' is not assignable to parameter of type 'Foo | Other'.
+  Type '{ a: string; b: string; }' is not assignable to type 'Foo'.
+    Types of property 'b' are incompatible.
+      Type 'string' is not assignable to type 'number'.
+tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(19,3): error TS2345: Argument of type '{ a: string; b: string; }' is not assignable to parameter of type 'Foo | Other'.
+  Type '{ a: string; b: string; }' is not assignable to type 'Foo'.
+    Types of property 'b' are incompatible.
+      Type 'string' is not assignable to type 'number'.
+tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts(24,5): error TS2345: Argument of type '{ a: string; b: string; }' is not assignable to parameter of type 'Bar | Other'.
+  Object literal may only specify known properties, and 'a' does not exist in type 'Bar | Other'.
+
+
+==== tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts (3 errors) ====
+    interface Foo {
+        a: string;
+        b: number;
+    };
+
+    interface Bar {
+        b: string;
+    }
+
+    interface Other {
+        totallyUnrelatedProperty: number;
+    }
+
+    export let x = { a: '', b: '' };
+
+    declare function f(x: Foo | Other): any;
+
+    f(x);
+      ~
+!!! error TS2345: Argument of type '{ a: string; b: string; }' is not assignable to parameter of type 'Foo | Other'.
+!!! error TS2345:   Type '{ a: string; b: string; }' is not assignable to type 'Foo'.
+!!! error TS2345:     Types of property 'b' are incompatible.
+!!! error TS2345:       Type 'string' is not assignable to type 'number'.
+    f({ a: '', b: '' })
+      ~~~~~~~~~~~~~~~~
+!!! error TS2345: Argument of type '{ a: string; b: string; }' is not assignable to parameter of type 'Foo | Other'.
+!!! error TS2345:   Type '{ a: string; b: string; }' is not assignable to type 'Foo'.
+!!! error TS2345:     Types of property 'b' are incompatible.
+!!! error TS2345:       Type 'string' is not assignable to type 'number'.
+
+    declare function g(x: Bar | Other): any;
+
+    g(x);
+    g({ a: '', b: '' })
+        ~~~~~
+!!! error TS2345: Argument of type '{ a: string; b: string; }' is not assignable to parameter of type 'Bar | Other'.
+!!! error TS2345:   Object literal may only specify known properties, and 'a' does not exist in type 'Bar | Other'.
+
+    declare function h(x: Foo | Bar | Other): any;
+
+    h(x);
+    h({ a: '', b: '' })
+

tests/baselines/reference/errorsOnUnionsOfOverlappingObjects01.js

@@ -0,0 +1,43 @@
+//// [errorsOnUnionsOfOverlappingObjects01.ts]
+interface Foo {
+    a: string;
+    b: number;
+};
+
+interface Bar {
+    b: string;
+}
+
+interface Other {
+    totallyUnrelatedProperty: number;
+}
+
+export let x = { a: '', b: '' };
+
+declare function f(x: Foo | Other): any;
+
+f(x);
+f({ a: '', b: '' })
+
+declare function g(x: Bar | Other): any;
+
+g(x);
+g({ a: '', b: '' })
+
+declare function h(x: Foo | Bar | Other): any;
+
+h(x);
+h({ a: '', b: '' })
+
+
+//// [errorsOnUnionsOfOverlappingObjects01.js]
+"use strict";
+exports.__esModule = true;
+;
+exports.x = { a: '', b: '' };
+f(exports.x);
+f({ a: '', b: '' });
+g(exports.x);
+g({ a: '', b: '' });
+h(exports.x);
+h({ a: '', b: '' });

tests/baselines/reference/errorsOnUnionsOfOverlappingObjects01.symbols

@@ -0,0 +1,77 @@
+=== tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts ===
+interface Foo {
+>Foo : Symbol(Foo, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 0, 0))
+
+    a: string;
+>a : Symbol(Foo.a, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 0, 15))
+
+    b: number;
+>b : Symbol(Foo.b, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 1, 14))
+
+};
+
+interface Bar {
+>Bar : Symbol(Bar, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 3, 2))
+
+    b: string;
+>b : Symbol(Bar.b, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 5, 15))
+}
+
+interface Other {
+>Other : Symbol(Other, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 7, 1))
+
+    totallyUnrelatedProperty: number;
+>totallyUnrelatedProperty : Symbol(Other.totallyUnrelatedProperty, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 9, 17))
+}
+
+export let x = { a: '', b: '' };
+>x : Symbol(x, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 13, 10))
+>a : Symbol(a, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 13, 16))
+>b : Symbol(b, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 13, 23))
+
+declare function f(x: Foo | Other): any;
+>f : Symbol(f, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 13, 32))
+>x : Symbol(x, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 15, 19))
+>Foo : Symbol(Foo, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 0, 0))
+>Other : Symbol(Other, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 7, 1))
+
+f(x);
+>f : Symbol(f, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 13, 32))
+>x : Symbol(x, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 13, 10))
+
+f({ a: '', b: '' })
+>f : Symbol(f, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 13, 32))
+>a : Symbol(a, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 18, 3))
+>b : Symbol(b, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 18, 10))
+
+declare function g(x: Bar | Other): any;
+>g : Symbol(g, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 18, 19))
+>x : Symbol(x, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 20, 19))
+>Bar : Symbol(Bar, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 3, 2))
+>Other : Symbol(Other, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 7, 1))
+
+g(x);
+>g : Symbol(g, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 18, 19))
+>x : Symbol(x, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 13, 10))
+
+g({ a: '', b: '' })
+>g : Symbol(g, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 18, 19))
+>a : Symbol(a, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 23, 3))
+>b : Symbol(b, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 23, 10))
+
+declare function h(x: Foo | Bar | Other): any;
+>h : Symbol(h, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 23, 19))
+>x : Symbol(x, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 25, 19))
+>Foo : Symbol(Foo, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 0, 0))
+>Bar : Symbol(Bar, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 3, 2))
+>Other : Symbol(Other, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 7, 1))
+
+h(x);
+>h : Symbol(h, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 23, 19))
+>x : Symbol(x, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 13, 10))
+
+h({ a: '', b: '' })
+>h : Symbol(h, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 23, 19))
+>a : Symbol(a, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 28, 3))
+>b : Symbol(b, Decl(errorsOnUnionsOfOverlappingObjects01.ts, 28, 10))
+