Widen inference candidates for error reporting

src/compiler/checker.ts

@@ -9596,12 +9596,8 @@ namespace ts {
             if (!strictNullChecks) {
                 return getSupertypeOrUnion(types);
             }
-            const primaryTypes = filter(types, t => !(t.flags & TypeFlags.Nullable));
-            if (!primaryTypes.length) {
-                return getUnionType(types, /*subtypeReduction*/ true);
-            }
-            const supertype = getSupertypeOrUnion(primaryTypes);
-            return supertype && includeFalsyTypes(supertype, getFalsyFlagsOfTypes(types) & TypeFlags.Nullable);
+            const supertype = getSupertypeOrUnion(map(types, getNonNullableType));
+            return supertype && includeFalsyTypes(supertype, getFalsyFlagsOfTypes(types) & (TypeFlags.Nullable | TypeFlags.Void));
         }
 
         function reportNoCommonSupertypeError(types: Type[], errorLocation: Node, errorMessageChainHead: DiagnosticMessageChain): void {
@@ -9624,6 +9620,7 @@ namespace ts {
                     }
                 }
 
+                Debug.assert(score < types.length, "types.length - 1 is the maximum score, given that getCommonSuperType returned false");
                 Debug.assert(!!downfallType, "If there is no common supertype, each type should have a downfallType");
 
                 if (score > bestSupertypeScore) {
@@ -9632,7 +9629,6 @@ namespace ts {
                     bestSupertypeScore = score;
                 }
 
-                // types.length - 1 is the maximum score, given that getCommonSupertype returned false
                 if (bestSupertypeScore === types.length - 1) {
                     break;
                 }
@@ -10322,9 +10318,20 @@ namespace ts {
             return type.flags & TypeFlags.Union ? getUnionType(reducedTypes) : getIntersectionType(reducedTypes);
         }
 
-        function getInferenceCandidates(context: InferenceContext, index: number): Type[] {
-            const inferences = context.inferences[index];
-            return inferences.primary || inferences.secondary || emptyArray;
+        /**
+         * 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 getInferenceCandidates(context: InferenceContext, index: number) {
+            const typeInferences = context.inferences[index];
+            const inferences: Type[] = typeInferences.primary || typeInferences.secondary || emptyArray;
+            const signature = context.signature;
+            const widenLiteralTypes = typeInferences.topLevel &&
+                !hasPrimitiveConstraint(signature.typeParameters[index]) &&
+                (typeInferences.isFixed || !isTypeParameterAtTopLevel(getReturnTypeOfSignature(signature), signature.typeParameters[index]));
+            return widenLiteralTypes ? sameMap(inferences, getWidenedLiteralType) : inferences;
         }
 
         function hasPrimitiveConstraint(type: TypeParameter): boolean {
@@ -10338,17 +10345,8 @@ namespace ts {
             if (!inferredType) {
                 const inferences = getInferenceCandidates(context, index);
                 if (inferences.length) {
-                    // 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 = context.inferences[index].topLevel &&
-                        !hasPrimitiveConstraint(signature.typeParameters[index]) &&
-                        (context.inferences[index].isFixed || !isTypeParameterAtTopLevel(getReturnTypeOfSignature(signature), signature.typeParameters[index]));
-                    const baseInferences = widenLiteralTypes ? sameMap(inferences, getWidenedLiteralType) : inferences;
                     // Infer widened union or supertype, or the unknown type for no common supertype
-                    const unionOrSuperType = context.inferUnionTypes ? getUnionType(baseInferences, /*subtypeReduction*/ true) : getCommonSupertype(baseInferences);
+                    const unionOrSuperType = context.inferUnionTypes ? getUnionType(inferences, /*subtypeReduction*/ true) : getCommonSupertype(inferences);
                     inferredType = unionOrSuperType ? getWidenedType(unionOrSuperType) : unknownType;
                     inferenceSucceeded = !!unionOrSuperType;
                 }

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.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/noCommonSupertypeTypeInferenceMatchesReporting.symbols

@@ -0,0 +1,28 @@
+=== tests/cases/compiler/noCommonSupertypeTypeInferenceMatchesReporting.ts ===
+// Fixes #15116, which asserted on line 5 but not 6
+declare function f<T>(a: T, b: T): boolean;
+>f : Symbol(f, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 0, 0))
+>T : Symbol(T, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 1, 19))
+>a : Symbol(a, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 1, 22))
+>T : Symbol(T, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 1, 19))
+>b : Symbol(b, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 1, 27))
+>T : Symbol(T, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 1, 19))
+
+function g(gut: { n: 12 | undefined }) {
+>g : Symbol(g, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 1, 43))
+>gut : Symbol(gut, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 2, 11))
+>n : Symbol(n, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 2, 17))
+
+    f(gut.n, 12); // ok, T = number | undefined
+>f : Symbol(f, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 0, 0))
+>gut.n : Symbol(n, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 2, 17))
+>gut : Symbol(gut, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 2, 11))
+>n : Symbol(n, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 2, 17))
+
+    f(12, gut.n); // ok, T = number | undefined
+>f : Symbol(f, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 0, 0))
+>gut.n : Symbol(n, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 2, 17))
+>gut : Symbol(gut, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 2, 11))
+>n : Symbol(n, Decl(noCommonSupertypeTypeInferenceMatchesReporting.ts, 2, 17))
+}
+

tests/baselines/reference/noCommonSupertypeTypeInferenceMatchesReporting.types

@@ -0,0 +1,32 @@
+=== tests/cases/compiler/noCommonSupertypeTypeInferenceMatchesReporting.ts ===
+// Fixes #15116, which asserted on line 5 but not 6
+declare function f<T>(a: T, b: T): boolean;
+>f : <T>(a: T, b: T) => boolean
+>T : T
+>a : T
+>T : T
+>b : T
+>T : T
+
+function g(gut: { n: 12 | undefined }) {
+>g : (gut: { n: 12 | undefined; }) => void
+>gut : { n: 12 | undefined; }
+>n : 12 | undefined
+
+    f(gut.n, 12); // ok, T = number | undefined
+>f(gut.n, 12) : boolean
+>f : <T>(a: T, b: T) => boolean
+>gut.n : 12 | undefined
+>gut : { n: 12 | undefined; }
+>n : 12 | undefined
+>12 : 12
+
+    f(12, gut.n); // ok, T = number | undefined
+>f(12, gut.n) : boolean
+>f : <T>(a: T, b: T) => boolean
+>12 : 12
+>gut.n : 12 | undefined
+>gut : { n: 12 | undefined; }
+>n : 12 | 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
+}