Widen inference candidates for error reporting

src/compiler/checker.ts

@@ -9920,7 +9920,7 @@ namespace ts {
                     bestSupertypeScore = score;
                 }
 
-                // types.length - 1 is the maximum score, given that getCommonSupertype returned false
+                Debug.assert(bestSupertypeScore < types.length, "types.length - 1 is the maximum score, given that getCommonSuperType returned false");
                 if (bestSupertypeScore === types.length - 1) {
                     break;
                 }
@@ -10631,6 +10631,19 @@ namespace ts {
             return type.flags & TypeFlags.Union ? getUnionType(reducedTypes) : getIntersectionType(reducedTypes);
         }
 
+        /**
+         * We widen inferred literal types if
+         * all inferences were made to top-level ocurrences of the type parameter, and
+         * the type parameter has no constraint or its constraint includes no primitive or literal types, and
+         * the type parameter was fixed during inference or does not occur at top-level in the return type.
+         */
+        function widenInferenceCandidates(inference: InferenceInfo, signature: Signature) {
+            const widenLiteralTypes = inference.topLevel &&
+                !hasPrimitiveConstraint(inference.typeParameter) &&
+                (inference.isFixed || !isTypeParameterAtTopLevel(getReturnTypeOfSignature(signature), inference.typeParameter));
+            return widenLiteralTypes ? sameMap(inference.candidates, getWidenedLiteralType) : inference.candidates;
+        }
+
         function hasPrimitiveConstraint(type: TypeParameter): boolean {
             const constraint = getConstraintOfTypeParameter(type);
             return constraint && maybeTypeOfKind(constraint, TypeFlags.Primitive | TypeFlags.Index);
@@ -10642,15 +10655,7 @@ namespace ts {
             let inferenceSucceeded: boolean;
             if (!inferredType) {
                 if (inference.candidates) {
-                    // We widen inferred literal types if
-                    // all inferences were made to top-level ocurrences of the type parameter, and
-                    // the type parameter has no constraint or its constraint includes no primitive or literal types, and
-                    // the type parameter was fixed during inference or does not occur at top-level in the return type.
-                    const signature = context.signature;
-                    const widenLiteralTypes = inference.topLevel &&
-                        !hasPrimitiveConstraint(inference.typeParameter) &&
-                        (inference.isFixed || !isTypeParameterAtTopLevel(getReturnTypeOfSignature(signature), inference.typeParameter));
-                    const baseCandidates = widenLiteralTypes ? sameMap(inference.candidates, getWidenedLiteralType) : inference.candidates;
+                    const baseCandidates = widenInferenceCandidates(inference, context.signature);
                     // Infer widened union or supertype, or the unknown type for no common supertype. We infer union types
                     // for inferences coming from return types in order to avoid common supertype failures.
                     const unionOrSuperType = context.flags & InferenceFlags.InferUnionTypes || inference.priority & InferencePriority.ReturnType ?
@@ -15649,7 +15654,7 @@ namespace ts {
                 else {
                     Debug.assert(resultOfFailedInference.failedTypeParameterIndex >= 0);
                     const failedTypeParameter = candidateForTypeArgumentError.typeParameters[resultOfFailedInference.failedTypeParameterIndex];
-                    const inferenceCandidates = resultOfFailedInference.inferences[resultOfFailedInference.failedTypeParameterIndex].candidates;
+                    const inferenceCandidates = widenInferenceCandidates(resultOfFailedInference.inferences[resultOfFailedInference.failedTypeParameterIndex], resultOfFailedInference.signature);
 
                     let diagnosticChainHead = chainDiagnosticMessages(/*details*/ undefined, // details will be provided by call to reportNoCommonSupertypeError
                         Diagnostics.The_type_argument_for_type_parameter_0_cannot_be_inferred_from_the_usage_Consider_specifying_the_type_arguments_explicitly,

tests/baselines/reference/fixTypeParameterInSignatureWithRestParameters.errors.txt

@@ -1,10 +1,10 @@
 tests/cases/compiler/fixTypeParameterInSignatureWithRestParameters.ts(2,1): error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
-  Type argument candidate '1' is not a valid type argument because it is not a supertype of candidate '""'.
+  Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'string'.
 
 
 ==== tests/cases/compiler/fixTypeParameterInSignatureWithRestParameters.ts (1 errors) ====
     function bar<T>(item1: T, item2: T) { }
     bar(1, ""); // Should be ok
     ~~~
 !!! error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
-!!! error TS2453:   Type argument candidate '1' is not a valid type argument because it is not a supertype of candidate '""'.
+!!! error TS2453:   Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'string'.

tests/baselines/reference/genericRestArgs.errors.txt

@@ -1,8 +1,8 @@
 tests/cases/compiler/genericRestArgs.ts(2,12): error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
-  Type argument candidate '1' is not a valid type argument because it is not a supertype of candidate '""'.
+  Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'string'.
 tests/cases/compiler/genericRestArgs.ts(5,34): error TS2345: Argument of type '""' is not assignable to parameter of type 'number'.
 tests/cases/compiler/genericRestArgs.ts(10,12): error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
-  Type argument candidate '1' is not a valid type argument because it is not a supertype of candidate '""'.
+  Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'string'.
 tests/cases/compiler/genericRestArgs.ts(12,30): error TS2345: Argument of type '1' is not assignable to parameter of type 'any[]'.
 
 
@@ -11,7 +11,7 @@ tests/cases/compiler/genericRestArgs.ts(12,30): error TS2345: Argument of type '
     var a1Ga = makeArrayG(1, ""); // no error
                ~~~~~~~~~~
 !!! error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
-!!! error TS2453:   Type argument candidate '1' is not a valid type argument because it is not a supertype of candidate '""'.
+!!! error TS2453:   Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'string'.
     var a1Gb = makeArrayG<any>(1, ""); 
     var a1Gc = makeArrayG<Object>(1, ""); 
     var a1Gd = makeArrayG<number>(1, ""); // error
@@ -24,7 +24,7 @@ tests/cases/compiler/genericRestArgs.ts(12,30): error TS2345: Argument of type '
     var a2Ga = makeArrayGOpt(1, ""); 
                ~~~~~~~~~~~~~
 !!! error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
-!!! error TS2453:   Type argument candidate '1' is not a valid type argument because it is not a supertype of candidate '""'.
+!!! error TS2453:   Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'string'.
     var a2Gb = makeArrayG<any>(1, "");
     var a2Gc = makeArrayG<any[]>(1, ""); // error
                                  ~

tests/baselines/reference/noCommonSupertypeTypeInferenceMatchesReporting.errors.txt

@@ -0,0 +1,22 @@
+tests/cases/compiler/noCommonSupertypeTypeInferenceMatchesReporting.ts(4,5): error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
+  Type argument candidate '12 | undefined' is not a valid type argument because it is not a supertype of candidate 'number'.
+tests/cases/compiler/noCommonSupertypeTypeInferenceMatchesReporting.ts(5,5): error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
+  Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate '12 | undefined'.
+    Type 'undefined' is not assignable to type 'number'.
+
+
+==== tests/cases/compiler/noCommonSupertypeTypeInferenceMatchesReporting.ts (2 errors) ====
+    // Fixes #15116, which asserted on line 5 but not 6
+    declare function f<T>(a: T, b: T): boolean;
+    function g(gut: { n: 12 | undefined }) {
+        f(gut.n, 12); // ok, T = number | undefined
+        ~
+!!! error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
+!!! error TS2453:   Type argument candidate '12 | undefined' is not a valid type argument because it is not a supertype of candidate 'number'.
+        f(12, gut.n); // ok, T = number | undefined
+        ~
+!!! error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
+!!! error TS2453:   Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate '12 | undefined'.
+!!! error TS2453:     Type 'undefined' is not assignable to type 'number'.
+    }
+

tests/baselines/reference/noCommonSupertypeTypeInferenceMatchesReporting.js

@@ -0,0 +1,14 @@
+//// [noCommonSupertypeTypeInferenceMatchesReporting.ts]
+// Fixes #15116, which asserted on line 5 but not 6
+declare function f<T>(a: T, b: T): boolean;
+function g(gut: { n: 12 | undefined }) {
+    f(gut.n, 12); // ok, T = number | undefined
+    f(12, gut.n); // ok, T = number | undefined
+}
+
+
+//// [noCommonSupertypeTypeInferenceMatchesReporting.js]
+function g(gut) {
+    f(gut.n, 12); // ok, T = number | undefined
+    f(12, gut.n); // ok, T = number | undefined
+}

tests/baselines/reference/parser15.4.4.14-9-2.errors.txt

@@ -1,5 +1,5 @@
 tests/cases/conformance/parser/ecmascript5/parser15.4.4.14-9-2.ts(16,15): error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
-  Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'false'.
+  Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'boolean'.
 tests/cases/conformance/parser/ecmascript5/parser15.4.4.14-9-2.ts(25,1): error TS2304: Cannot find name 'runTestCase'.
 
 
@@ -22,7 +22,7 @@ tests/cases/conformance/parser/ecmascript5/parser15.4.4.14-9-2.ts(25,1): error T
       var a = new Array(false,undefined,null,"0",obj,-1.3333333333333, "str",-0,true,+0, one, 1,0, false, _float, -(4/3));
                   ~~~~~
 !!! error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
-!!! error TS2453:   Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'false'.
+!!! error TS2453:   Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'boolean'.
       if (a.indexOf(-(4/3)) === 14 &&      // a[14]=_float===-(4/3)
           a.indexOf(0) === 7      &&       // a[7] = +0, 0===+0
           a.indexOf(-0) === 7      &&     // a[7] = +0, -0===+0

tests/cases/compiler/noCommonSupertypeTypeInferenceMatchesReporting.ts

@@ -0,0 +1,7 @@
+// @strictNullChecks: true
+// Fixes #15116, which asserted on line 5 but not 6
+declare function f<T>(a: T, b: T): boolean;
+function g(gut: { n: 12 | undefined }) {
+    f(gut.n, 12); // ok, T = number | undefined
+    f(12, gut.n); // ok, T = number | undefined
+}