Intersect 'this' types in union signatures

src/compiler/checker.ts

@@ -7169,8 +7169,9 @@ namespace ts {
             }
             let result: Signature[] | undefined;
             for (let i = 0; i < signatureLists.length; i++) {
-                // Allow matching non-generic signatures to have excess parameters and different return types
-                const match = i === listIndex ? signature : findMatchingSignature(signatureLists[i], signature, /*partialMatch*/ true, /*ignoreThisTypes*/ true, /*ignoreReturnTypes*/ true);
+                // Allow matching non-generic signatures to have excess parameters and different return types.
+                // Prefer matching this types if possible.
+                const match = i === listIndex ? signature : findMatchingSignature(signatureLists[i], signature, /*partialMatch*/ true, /*ignoreThisTypes*/ false, /*ignoreReturnTypes*/ true);
                 if (!match) {
                     return undefined;
                 }
@@ -7193,7 +7194,7 @@ namespace ts {
                 }
                 for (const signature of signatureLists[i]) {
                     // Only process signatures with parameter lists that aren't already in the result list
-                    if (!result || !findMatchingSignature(result, signature, /*partialMatch*/ false, /*ignoreThisTypes*/ true, /*ignoreReturnTypes*/ true)) {
+                    if (!result || !findMatchingSignature(result, signature, /*partialMatch*/ false, /*ignoreThisTypes*/ false, /*ignoreReturnTypes*/ true)) {
                         const unionSignatures = findMatchingSignatures(signatureLists, signature, i);
                         if (unionSignatures) {
                             let s = signature;
@@ -7202,7 +7203,7 @@ namespace ts {
                                 let thisParameter = signature.thisParameter;
                                 const firstThisParameterOfUnionSignatures = forEach(unionSignatures, sig => sig.thisParameter);
                                 if (firstThisParameterOfUnionSignatures) {
-                                    const thisType = getUnionType(map(unionSignatures, sig => sig.thisParameter ? getTypeOfSymbol(sig.thisParameter) : anyType), UnionReduction.Subtype);
+                                    const thisType = getIntersectionType(mapDefined(unionSignatures, sig => sig.thisParameter && getTypeOfSymbol(sig.thisParameter)));
                                     thisParameter = createSymbolWithType(firstThisParameterOfUnionSignatures, thisType);
                                 }
                                 s = createUnionSignature(signature, unionSignatures);
@@ -7241,8 +7242,8 @@ namespace ts {
             }
             // A signature `this` type might be a read or a write position... It's very possible that it should be invariant
             // and we should refuse to merge signatures if there are `this` types and they do not match. However, so as to be
-            // permissive when calling, for now, we'll union the `this` types just like the overlapping-union-signature check does
-            const thisType = getUnionType([getTypeOfSymbol(left), getTypeOfSymbol(right)], UnionReduction.Subtype);
+            // permissive when calling, for now, we'll intersect the `this` types just like we do for param types in union signatures.
+            const thisType = getIntersectionType([getTypeOfSymbol(left), getTypeOfSymbol(right)]);
             return createSymbolWithType(left, thisType);
         }
 

tests/baselines/reference/unionThisTypeInFunctions.errors.txt

@@ -0,0 +1,34 @@
+tests/cases/conformance/types/thisType/unionThisTypeInFunctions.ts(10,5): error TS2684: The 'this' context of type 'Real | Fake' is not assignable to method's 'this' of type 'Real & Fake'.
+  Type 'Real' is not assignable to type 'Real & Fake'.
+    Type 'Real' is not assignable to type 'Fake'.
+      Types of property 'method' are incompatible.
+        Type '(this: Real, n: number) => void' is not assignable to type '(this: Fake, n: number) => void'.
+          The 'this' types of each signature are incompatible.
+            Type 'Fake' is not assignable to type 'Real'.
+              Types of property 'data' are incompatible.
+                Type 'number' is not assignable to type 'string'.
+
+
+==== tests/cases/conformance/types/thisType/unionThisTypeInFunctions.ts (1 errors) ====
+    interface Real {
+        method(this: this, n: number): void;
+        data: string;
+    }
+    interface Fake {
+        method(this: this, n: number): void;
+        data: number;
+    }
+    function test(r: Real | Fake) {
+        r.method(12); // error
+        ~
+!!! error TS2684: The 'this' context of type 'Real | Fake' is not assignable to method's 'this' of type 'Real & Fake'.
+!!! error TS2684:   Type 'Real' is not assignable to type 'Real & Fake'.
+!!! error TS2684:     Type 'Real' is not assignable to type 'Fake'.
+!!! error TS2684:       Types of property 'method' are incompatible.
+!!! error TS2684:         Type '(this: Real, n: number) => void' is not assignable to type '(this: Fake, n: number) => void'.
+!!! error TS2684:           The 'this' types of each signature are incompatible.
+!!! error TS2684:             Type 'Fake' is not assignable to type 'Real'.
+!!! error TS2684:               Types of property 'data' are incompatible.
+!!! error TS2684:                 Type 'number' is not assignable to type 'string'.
+    }
+

tests/baselines/reference/unionThisTypeInFunctions.js

@@ -8,11 +8,11 @@ interface Fake {
     data: number;
 }
 function test(r: Real | Fake) {
-    r.method(12);
+    r.method(12); // error
 }
 
 
 //// [unionThisTypeInFunctions.js]
 function test(r) {
-    r.method(12);
+    r.method(12); // error
 }

tests/baselines/reference/unionThisTypeInFunctions.symbols

@@ -27,7 +27,7 @@ function test(r: Real | Fake) {
 >Real : Symbol(Real, Decl(unionThisTypeInFunctions.ts, 0, 0))
 >Fake : Symbol(Fake, Decl(unionThisTypeInFunctions.ts, 3, 1))
 
-    r.method(12);
+    r.method(12); // error
 >r.method : Symbol(method, Decl(unionThisTypeInFunctions.ts, 0, 16), Decl(unionThisTypeInFunctions.ts, 4, 16))
 >r : Symbol(r, Decl(unionThisTypeInFunctions.ts, 8, 14))
 >method : Symbol(method, Decl(unionThisTypeInFunctions.ts, 0, 16), Decl(unionThisTypeInFunctions.ts, 4, 16))

tests/baselines/reference/unionThisTypeInFunctions.types

@@ -21,8 +21,8 @@ function test(r: Real | Fake) {
 >test : (r: Real | Fake) => void
 >r : Real | Fake
 
-    r.method(12);
->r.method(12) : void
+    r.method(12); // error
+>r.method(12) : any
 >r.method : ((this: Real, n: number) => void) | ((this: Fake, n: number) => void)
 >r : Real | Fake
 >method : ((this: Real, n: number) => void) | ((this: Fake, n: number) => void)

tests/baselines/reference/unionTypeCallSignatures5.errors.txt

@@ -0,0 +1,19 @@
+tests/cases/conformance/types/union/unionTypeCallSignatures5.ts(12,1): error TS2684: The 'this' context of type 'void' is not assignable to method's 'this' of type 'never'.
+
+
+==== tests/cases/conformance/types/union/unionTypeCallSignatures5.ts (1 errors) ====
+    // #31485
+    interface A {
+      (this: void, b?: number): void;
+    }
+    interface B {
+      (this: number, b?: number): void;
+    }
+    interface C {
+      (i: number): void;
+    }
+    declare const fn: A | B | C;
+    fn(0);
+    ~~~~~
+!!! error TS2684: The 'this' context of type 'void' is not assignable to method's 'this' of type 'never'.
+

tests/baselines/reference/unionTypeCallSignatures5.types

@@ -18,7 +18,7 @@ declare const fn: A | B | C;
 >fn : A | B | C
 
 fn(0);
->fn(0) : void
+>fn(0) : any
 >fn : A | B | C
 >0 : 0
 

tests/baselines/reference/unionTypeCallSignatures6.errors.txt

@@ -0,0 +1,98 @@
+tests/cases/conformance/types/union/unionTypeCallSignatures6.ts(11,1): error TS2684: The 'this' context of type 'void' is not assignable to method's 'this' of type 'A & B'.
+  Type 'void' is not assignable to type 'A'.
+tests/cases/conformance/types/union/unionTypeCallSignatures6.ts(13,1): error TS2684: The 'this' context of type 'void' is not assignable to method's 'this' of type 'A'.
+tests/cases/conformance/types/union/unionTypeCallSignatures6.ts(38,4): error TS2349: This expression is not callable.
+  Each member of the union type 'F3 | F4' has signatures, but none of those signatures are compatible with each other.
+tests/cases/conformance/types/union/unionTypeCallSignatures6.ts(39,1): error TS2684: The 'this' context of type 'A & C & { f0: F0 | F3; f1: F1 | F3; f2: F1 | F4; f3: F3 | F4; f4: F3 | F5; }' is not assignable to method's 'this' of type 'B'.
+  Property 'b' is missing in type 'A & C & { f0: F0 | F3; f1: F1 | F3; f2: F1 | F4; f3: F3 | F4; f4: F3 | F5; }' but required in type 'B'.
+tests/cases/conformance/types/union/unionTypeCallSignatures6.ts(48,1): error TS2684: The 'this' context of type 'void' is not assignable to method's 'this' of type 'A & B'.
+  Type 'void' is not assignable to type 'A'.
+tests/cases/conformance/types/union/unionTypeCallSignatures6.ts(55,1): error TS2769: No overload matches this call.
+  Overload 1 of 2, '(this: A & B & C): void', gave the following error.
+    The 'this' context of type 'void' is not assignable to method's 'this' of type 'A & B & C'.
+      Type 'void' is not assignable to type 'A'.
+  Overload 2 of 2, '(this: A & B): void', gave the following error.
+    The 'this' context of type 'void' is not assignable to method's 'this' of type 'A & B'.
+      Type 'void' is not assignable to type 'A'.
+
+
+==== tests/cases/conformance/types/union/unionTypeCallSignatures6.ts (6 errors) ====
+    type A = { a: string };
+    type B = { b: number };
+    type C = { c: string };
+    type D = { d: number };
+    type F0 = () => void;
+
+    // #31547
+    type F1 = (this: A) => void;
+    type F2 = (this: B) => void;
+    declare var f1: F1 | F2;
+    f1(); // error
+    ~~~~
+!!! error TS2684: The 'this' context of type 'void' is not assignable to method's 'this' of type 'A & B'.
+!!! error TS2684:   Type 'void' is not assignable to type 'A'.
+    declare var f2: F0 | F1;
+    f2(); // error
+    ~~~~
+!!! error TS2684: The 'this' context of type 'void' is not assignable to method's 'this' of type 'A'.
+
+    interface F3 {
+      (this: A): void;
+      (this: B): void;
+    }
+    interface F4 {
+      (this: C): void;
+      (this: D): void;
+    }
+    interface F5 {
+      (this: C): void;
+      (this: B): void;
+    }
+
+    declare var x1: A & C & {
+      f0: F0 | F3;
+      f1: F1 | F3;
+      f2: F1 | F4;
+      f3: F3 | F4;
+      f4: F3 | F5;
+    }
+    x1.f0();
+    x1.f1();
+    x1.f2();
+    x1.f3(); // error
+       ~~
+!!! error TS2349: This expression is not callable.
+!!! error TS2349:   Each member of the union type 'F3 | F4' has signatures, but none of those signatures are compatible with each other.
+    x1.f4(); // error
+    ~~
+!!! error TS2684: The 'this' context of type 'A & C & { f0: F0 | F3; f1: F1 | F3; f2: F1 | F4; f3: F3 | F4; f4: F3 | F5; }' is not assignable to method's 'this' of type 'B'.
+!!! error TS2684:   Property 'b' is missing in type 'A & C & { f0: F0 | F3; f1: F1 | F3; f2: F1 | F4; f3: F3 | F4; f4: F3 | F5; }' but required in type 'B'.
+!!! related TS2728 tests/cases/conformance/types/union/unionTypeCallSignatures6.ts:2:12: 'b' is declared here.
+
+    declare var x2: A & B & {
+      f4: F3 | F5;
+    }
+    x2.f4();
+
+    type F6 = (this: A & B) => void;
+    declare var f3: F1 | F6;
+    f3(); // error
+    ~~~~
+!!! error TS2684: The 'this' context of type 'void' is not assignable to method's 'this' of type 'A & B'.
+!!! error TS2684:   Type 'void' is not assignable to type 'A'.
+
+    interface F7 {
+      (this: A & B & C): void;
+      (this: A & B): void;
+    }
+    declare var f4: F6 | F7;
+    f4(); // error
+    ~~~~
+!!! error TS2769: No overload matches this call.
+!!! error TS2769:   Overload 1 of 2, '(this: A & B & C): void', gave the following error.
+!!! error TS2769:     The 'this' context of type 'void' is not assignable to method's 'this' of type 'A & B & C'.
+!!! error TS2769:       Type 'void' is not assignable to type 'A'.
+!!! error TS2769:   Overload 2 of 2, '(this: A & B): void', gave the following error.
+!!! error TS2769:     The 'this' context of type 'void' is not assignable to method's 'this' of type 'A & B'.
+!!! error TS2769:       Type 'void' is not assignable to type 'A'.
+

tests/baselines/reference/unionTypeCallSignatures6.js

@@ -0,0 +1,69 @@
+//// [unionTypeCallSignatures6.ts]
+type A = { a: string };
+type B = { b: number };
+type C = { c: string };
+type D = { d: number };
+type F0 = () => void;
+
+// #31547
+type F1 = (this: A) => void;
+type F2 = (this: B) => void;
+declare var f1: F1 | F2;
+f1(); // error
+declare var f2: F0 | F1;
+f2(); // error
+
+interface F3 {
+  (this: A): void;
+  (this: B): void;
+}
+interface F4 {
+  (this: C): void;
+  (this: D): void;
+}
+interface F5 {
+  (this: C): void;
+  (this: B): void;
+}
+
+declare var x1: A & C & {
+  f0: F0 | F3;
+  f1: F1 | F3;
+  f2: F1 | F4;
+  f3: F3 | F4;
+  f4: F3 | F5;
+}
+x1.f0();
+x1.f1();
+x1.f2();
+x1.f3(); // error
+x1.f4(); // error
+
+declare var x2: A & B & {
+  f4: F3 | F5;
+}
+x2.f4();
+
+type F6 = (this: A & B) => void;
+declare var f3: F1 | F6;
+f3(); // error
+
+interface F7 {
+  (this: A & B & C): void;
+  (this: A & B): void;
+}
+declare var f4: F6 | F7;
+f4(); // error
+
+
+//// [unionTypeCallSignatures6.js]
+f1(); // error
+f2(); // error
+x1.f0();
+x1.f1();
+x1.f2();
+x1.f3(); // error
+x1.f4(); // error
+x2.f4();
+f3(); // error
+f4(); // error