Fix #33436

src/compiler/checker.ts

@@ -699,7 +699,7 @@ namespace ts {
         // in getPropagatingFlagsOfTypes, and it is checked in inferFromTypes.
         anyFunctionType.objectFlags |= ObjectFlags.NonInferrableType;
 
-        const noConstraintType = createAnonymousType(undefined, emptySymbols, emptyArray, emptyArray, undefined, undefined);
+        const noConstraintType = createIntrinsicType(TypeFlags.Unknown, "unknown");
         const circularConstraintType = createAnonymousType(undefined, emptySymbols, emptyArray, emptyArray, undefined, undefined);
         const resolvingDefaultType = createAnonymousType(undefined, emptySymbols, emptyArray, emptyArray, undefined, undefined);
 

tests/baselines/reference/assignmentCompatWithCallSignatures3.errors.txt

@@ -14,7 +14,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
   Types of parameters 'x' and 'x' are incompatible.
     Types of parameters 'arg' and 'arg' are incompatible.
       Type 'string' is not assignable to type 'T'.
-        'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+        'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures3.ts(62,1): error TS2322: Type '(x: (arg: Base) => Derived) => Base' is not assignable to type '<T extends Base, U extends Derived>(x: (arg: T) => U) => T'.
   Types of parameters 'x' and 'x' are incompatible.
     Types of parameters 'arg' and 'arg' are incompatible.
@@ -143,7 +143,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322:   Types of parameters 'x' and 'x' are incompatible.
 !!! error TS2322:     Types of parameters 'arg' and 'arg' are incompatible.
 !!! error TS2322:       Type 'string' is not assignable to type 'T'.
-!!! error TS2322:         'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+!!! error TS2322:         'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
     var b6: <T extends Base, U extends Derived>(x: (arg: T) => U) => T; 
     a6 = b6; // ok
     b6 = a6; // ok

tests/baselines/reference/assignmentCompatWithCallSignatures4.errors.txt

@@ -47,7 +47,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures4.ts(89,9): error TS2322: Type '<T>(x: T) => string[]' is not assignable to type '<T>(x: T) => T[]'.
   Type 'string[]' is not assignable to type 'T[]'.
     Type 'string' is not assignable to type 'T'.
-      'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+      'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures4.ts(90,9): error TS2322: Type '<T>(x: T) => T[]' is not assignable to type '<T>(x: T) => string[]'.
   Type 'T[]' is not assignable to type 'string[]'.
     Type 'T' is not assignable to type 'string'.
@@ -57,7 +57,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures4.ts(96,9): error TS2322: Type '<T>(x: T) => string[]' is not assignable to type '<T>(x: T) => T[]'.
   Type 'string[]' is not assignable to type 'T[]'.
     Type 'string' is not assignable to type 'T'.
-      'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+      'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 
 
 ==== tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures4.ts (15 errors) ====
@@ -211,7 +211,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322: Type '<T>(x: T) => string[]' is not assignable to type '<T>(x: T) => T[]'.
 !!! error TS2322:   Type 'string[]' is not assignable to type 'T[]'.
 !!! error TS2322:     Type 'string' is not assignable to type 'T'.
-!!! error TS2322:       'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+!!! error TS2322:       'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
             b2 = a2;
             ~~
 !!! error TS2322: Type '<T>(x: T) => T[]' is not assignable to type '<T>(x: T) => string[]'.
@@ -231,6 +231,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322: Type '<T>(x: T) => string[]' is not assignable to type '<T>(x: T) => T[]'.
 !!! error TS2322:   Type 'string[]' is not assignable to type 'T[]'.
 !!! error TS2322:     Type 'string' is not assignable to type 'T'.
-!!! error TS2322:       'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+!!! error TS2322:       'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
         }
     }

tests/baselines/reference/assignmentCompatWithCallSignatures5.errors.txt

@@ -1,17 +1,18 @@
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures5.ts(40,1): error TS2322: Type '<T>(x: T) => void' is not assignable to type '<T>(x: T) => T'.
   Type 'void' is not assignable to type 'T'.
+    'void' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures5.ts(52,1): error TS2322: Type '<T>(x: { foo: T; }, y: { foo: T; bar: T; }) => Base' is not assignable to type '<T, U>(x: { foo: T; }, y: { foo: U; bar: U; }) => Base'.
   Types of parameters 'y' and 'y' are incompatible.
     Type '{ foo: U; bar: U; }' is not assignable to type '{ foo: T; bar: T; }'.
       Types of property 'foo' are incompatible.
         Type 'U' is not assignable to type 'T'.
-          'U' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+          'U' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures5.ts(55,1): error TS2322: Type '<T>(x: { a: T; b: T; }) => T[]' is not assignable to type '<U, V>(x: { a: U; b: V; }) => U[]'.
   Types of parameters 'x' and 'x' are incompatible.
     Type '{ a: U; b: V; }' is not assignable to type '{ a: U; b: U; }'.
       Types of property 'b' are incompatible.
         Type 'V' is not assignable to type 'U'.
-          'V' is assignable to the constraint of type 'U', but 'U' could be instantiated with a different subtype of constraint '{}'.
+          'V' is assignable to the constraint of type 'U', but 'U' could be instantiated with a different subtype of constraint 'unknown'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures5.ts(58,1): error TS2322: Type '<T extends Base>(x: { a: T; b: T; }) => T[]' is not assignable to type '<U, V>(x: { a: U; b: V; }) => U[]'.
   Types of parameters 'x' and 'x' are incompatible.
     Type '{ a: U; b: V; }' is not assignable to type '{ a: Base; b: Base; }'.
@@ -63,6 +64,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
     ~~
 !!! error TS2322: Type '<T>(x: T) => void' is not assignable to type '<T>(x: T) => T'.
 !!! error TS2322:   Type 'void' is not assignable to type 'T'.
+!!! error TS2322:     'void' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
     var b4: <T, U>(x: T, y: U) => string; 
     a4 = b4; // ok
     b4 = a4; // ok
@@ -81,7 +83,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322:     Type '{ foo: U; bar: U; }' is not assignable to type '{ foo: T; bar: T; }'.
 !!! error TS2322:       Types of property 'foo' are incompatible.
 !!! error TS2322:         Type 'U' is not assignable to type 'T'.
-!!! error TS2322:           'U' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+!!! error TS2322:           'U' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
     var b15: <U, V>(x: { a: U; b: V; }) => U[]; 
     a15 = b15; // ok, T = U, T = V
     b15 = a15; // ok
@@ -91,7 +93,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322:     Type '{ a: U; b: V; }' is not assignable to type '{ a: U; b: U; }'.
 !!! error TS2322:       Types of property 'b' are incompatible.
 !!! error TS2322:         Type 'V' is not assignable to type 'U'.
-!!! error TS2322:           'V' is assignable to the constraint of type 'U', but 'U' could be instantiated with a different subtype of constraint '{}'.
+!!! error TS2322:           'V' is assignable to the constraint of type 'U', but 'U' could be instantiated with a different subtype of constraint 'unknown'.
     var b16: <T>(x: { a: T; b: T }) => T[]; 
     a15 = b16; // ok
     b15 = a16; // ok

tests/baselines/reference/assignmentCompatWithCallSignatures6.errors.txt

@@ -1,11 +1,12 @@
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures6.ts(30,1): error TS2322: Type '<T>(x: T) => void' is not assignable to type '<T>(x: T) => T'.
   Type 'void' is not assignable to type 'T'.
+    'void' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures6.ts(39,1): error TS2322: Type '<T>(x: { foo: T; }, y: { foo: T; bar: T; }) => Base' is not assignable to type '<T, U>(x: { foo: T; }, y: { foo: U; bar: U; }) => Base'.
   Types of parameters 'y' and 'y' are incompatible.
     Type '{ foo: U; bar: U; }' is not assignable to type '{ foo: T; bar: T; }'.
       Types of property 'foo' are incompatible.
         Type 'U' is not assignable to type 'T'.
-          'U' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+          'U' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignatures6.ts(42,1): error TS2322: Type '<T extends Base>(x: { a: T; b: T; }) => T[]' is not assignable to type '<T>(x: { a: T; b: T; }) => T[]'.
   Types of parameters 'x' and 'x' are incompatible.
     Type '{ a: T; b: T; }' is not assignable to type '{ a: Base; b: Base; }'.
@@ -47,6 +48,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
     ~~
 !!! error TS2322: Type '<T>(x: T) => void' is not assignable to type '<T>(x: T) => T'.
 !!! error TS2322:   Type 'void' is not assignable to type 'T'.
+!!! error TS2322:     'void' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
     var b4: <T, U>(x: T, y: U) => string; 
     x.a4 = b4;
     b4 = x.a4;
@@ -62,7 +64,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322:     Type '{ foo: U; bar: U; }' is not assignable to type '{ foo: T; bar: T; }'.
 !!! error TS2322:       Types of property 'foo' are incompatible.
 !!! error TS2322:         Type 'U' is not assignable to type 'T'.
-!!! error TS2322:           'U' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+!!! error TS2322:           'U' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
     var b16: <T>(x: { a: T; b: T }) => T[]; 
     x.a16 = b16;
     b16 = x.a16;

tests/baselines/reference/assignmentCompatWithConstructSignatures3.errors.txt

@@ -14,7 +14,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
   Types of parameters 'x' and 'x' are incompatible.
     Types of parameters 'arg' and 'arg' are incompatible.
       Type 'string' is not assignable to type 'T'.
-        'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+        'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignatures3.ts(62,1): error TS2322: Type 'new (x: (arg: Base) => Derived) => Base' is not assignable to type 'new <T extends Base, U extends Derived>(x: (arg: T) => U) => T'.
   Types of parameters 'x' and 'x' are incompatible.
     Types of parameters 'arg' and 'arg' are incompatible.
@@ -143,7 +143,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322:   Types of parameters 'x' and 'x' are incompatible.
 !!! error TS2322:     Types of parameters 'arg' and 'arg' are incompatible.
 !!! error TS2322:       Type 'string' is not assignable to type 'T'.
-!!! error TS2322:         'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+!!! error TS2322:         'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
     var b6: new <T extends Base, U extends Derived>(x: (arg: T) => U) => T; 
     a6 = b6; // ok
     b6 = a6; // ok

tests/baselines/reference/assignmentCompatWithConstructSignatures4.errors.txt

@@ -63,7 +63,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignatures4.ts(89,9): error TS2322: Type 'new <T>(x: T) => string[]' is not assignable to type 'new <T>(x: T) => T[]'.
   Type 'string[]' is not assignable to type 'T[]'.
     Type 'string' is not assignable to type 'T'.
-      'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+      'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignatures4.ts(90,9): error TS2322: Type 'new <T>(x: T) => T[]' is not assignable to type 'new <T>(x: T) => string[]'.
   Type 'T[]' is not assignable to type 'string[]'.
     Type 'T' is not assignable to type 'string'.
@@ -73,7 +73,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignatures4.ts(96,9): error TS2322: Type 'new <T>(x: T) => string[]' is not assignable to type 'new <T>(x: T) => T[]'.
   Type 'string[]' is not assignable to type 'T[]'.
     Type 'string' is not assignable to type 'T'.
-      'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+      'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
 
 
 ==== tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignatures4.ts (19 errors) ====
@@ -247,7 +247,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322: Type 'new <T>(x: T) => string[]' is not assignable to type 'new <T>(x: T) => T[]'.
 !!! error TS2322:   Type 'string[]' is not assignable to type 'T[]'.
 !!! error TS2322:     Type 'string' is not assignable to type 'T'.
-!!! error TS2322:       'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+!!! error TS2322:       'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
             b2 = a2; // ok
             ~~
 !!! error TS2322: Type 'new <T>(x: T) => T[]' is not assignable to type 'new <T>(x: T) => string[]'.
@@ -267,6 +267,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322: Type 'new <T>(x: T) => string[]' is not assignable to type 'new <T>(x: T) => T[]'.
 !!! error TS2322:   Type 'string[]' is not assignable to type 'T[]'.
 !!! error TS2322:     Type 'string' is not assignable to type 'T'.
-!!! error TS2322:       'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
+!!! error TS2322:       'string' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'unknown'.
         }
     }