Port union reduction to 1.7

package.json

@@ -35,7 +35,7 @@
         "browserify": "latest",
         "istanbul": "latest",
         "mocha-fivemat-progress-reporter": "latest",
-        "tslint": "latest",
+        "tslint": "~2",
         "tsd": "latest"
     },
     "scripts": {

src/compiler/checker.ts

@@ -43,6 +43,8 @@ namespace ts {
         let emptyArray: any[] = [];
         let emptySymbols: SymbolTable = {};
 
+        let jsxElementClassType: Type = undefined;
+
         let compilerOptions = host.getCompilerOptions();
         let languageVersion = compilerOptions.target || ScriptTarget.ES3;
         let modulekind = compilerOptions.module ? compilerOptions.module : languageVersion === ScriptTarget.ES6 ? ModuleKind.ES6 : ModuleKind.None;
@@ -4938,9 +4940,6 @@ namespace ts {
                     }
                     return objectTypeRelatedTo(<ObjectType>source, <ObjectType>target, /*reportErrors*/ false);
                 }
-                if (source.flags & TypeFlags.TypeParameter && target.flags & TypeFlags.TypeParameter) {
-                    return typeParameterIdenticalTo(<TypeParameter>source, <TypeParameter>target);
-                }
                 if (source.flags & TypeFlags.Union && target.flags & TypeFlags.Union ||
                     source.flags & TypeFlags.Intersection && target.flags & TypeFlags.Intersection) {
                     if (result = eachTypeRelatedToSomeType(<UnionOrIntersectionType>source, <UnionOrIntersectionType>target)) {
@@ -5071,20 +5070,6 @@ namespace ts {
                 return result;
             }
 
-            function typeParameterIdenticalTo(source: TypeParameter, target: TypeParameter): Ternary {
-                if (source.symbol.name !== target.symbol.name) {
-                    return Ternary.False;
-                }
-                // covers case when both type parameters does not have constraint (both equal to noConstraintType)
-                if (source.constraint === target.constraint) {
-                    return Ternary.True;
-                }
-                if (source.constraint === noConstraintType || target.constraint === noConstraintType) {
-                    return Ternary.False;
-                }
-                return isIdenticalTo(source.constraint, target.constraint);
-            }
-
             // Determine if two object types are related by structure. First, check if the result is already available in the global cache.
             // Second, check if we have already started a comparison of the given two types in which case we assume the result to be true.
             // Third, check if both types are part of deeply nested chains of generic type instantiations and if so assume the types are
@@ -5607,27 +5592,20 @@ namespace ts {
                     return Ternary.False;
                 }
             }
-            let result = Ternary.True;
-            if (source.typeParameters && target.typeParameters) {
-                if (source.typeParameters.length !== target.typeParameters.length) {
-                    return Ternary.False;
-                }
-                for (let i = 0, len = source.typeParameters.length; i < len; ++i) {
-                    let related = compareTypes(source.typeParameters[i], target.typeParameters[i]);
-                    if (!related) {
-                        return Ternary.False;
-                    }
-                    result &= related;
-                }
-            }
-            else if (source.typeParameters || target.typeParameters) {
+            // Check that the two signatures have the same number of type parameters. We might consider
+            // also checking that any type parameter constraints match, but that would require instantiating
+            // the constraints with a common set of type arguments to get relatable entities in places where
+            // type parameters occur in the constraints. The complexity of doing that doesn't seem worthwhile,
+            // particularly as we're comparing erased versions of the signatures below.
+            if ((source.typeParameters ? source.typeParameters.length : 0) !== (target.typeParameters ? target.typeParameters.length : 0)) {
                 return Ternary.False;
             }
             // Spec 1.0 Section 3.8.3 & 3.8.4:
             // M and N (the signatures) are instantiated using type Any as the type argument for all type parameters declared by M and N
             source = getErasedSignature(source);
             target = getErasedSignature(target);
-            let targetLen = target.parameters.length;
+            let result = Ternary.True;
+            const targetLen = target.parameters.length;
             for (let i = 0; i < targetLen; i++) {
                 let s = isRestParameterIndex(source, i) ? getRestTypeOfSignature(source) : getTypeOfSymbol(source.parameters[i]);
                 let t = isRestParameterIndex(target, i) ? getRestTypeOfSignature(target) : getTypeOfSymbol(target.parameters[i]);
@@ -5928,6 +5906,17 @@ namespace ts {
             }
 
             function inferFromTypes(source: Type, target: Type) {
+                if (source.flags & TypeFlags.Union && target.flags & TypeFlags.Union ||
+                    source.flags & TypeFlags.Intersection && target.flags & TypeFlags.Intersection) {
+                    // Source and target are both unions or both intersections. To improve the quality of
+                    // inferences we first reduce the types by removing constituents that are identically
+                    // matched by a constituent in the other type. For example, when inferring from
+                    // 'string | string[]' to 'string | T', we reduce the types to 'string[]' and 'T'.
+                    const reducedSource = reduceUnionOrIntersectionType(<UnionOrIntersectionType>source, <UnionOrIntersectionType>target);
+                    const reducedTarget = reduceUnionOrIntersectionType(<UnionOrIntersectionType>target, <UnionOrIntersectionType>source);
+                    source = reducedSource;
+                    target = reducedTarget;
+                }
                 if (target.flags & TypeFlags.TypeParameter) {
                     // If target is a type parameter, make an inference, unless the source type contains
                     // the anyFunctionType (the wildcard type that's used to avoid contextually typing functions).
@@ -5938,8 +5927,7 @@ namespace ts {
                     if (source.flags & TypeFlags.ContainsAnyFunctionType) {
                         return;
                     }
-
-                    let typeParameters = context.typeParameters;
+                    const typeParameters = context.typeParameters;
                     for (let i = 0; i < typeParameters.length; i++) {
                         if (target === typeParameters[i]) {
                             let inferences = context.inferences[i];
@@ -6086,6 +6074,41 @@ namespace ts {
             }
         }
 
+        function typeIdenticalToSomeType(source: Type, target: UnionOrIntersectionType): boolean {
+            for (const t of target.types) {
+                if (isTypeIdenticalTo(source, t)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        /**
+         * Return the reduced form of the source type. This type is computed by by removing all source
+         * constituents that have an identical match in the target type.
+         */
+        function reduceUnionOrIntersectionType(source: UnionOrIntersectionType, target: UnionOrIntersectionType) {
+            let sourceTypes = source.types;
+            let sourceIndex = 0;
+            let modified = false;
+            while (sourceIndex < sourceTypes.length) {
+                if (typeIdenticalToSomeType(sourceTypes[sourceIndex], target)) {
+                    if (!modified) {
+                        sourceTypes = sourceTypes.slice(0);
+                        modified = true;
+                    }
+                    sourceTypes.splice(sourceIndex, 1);
+                }
+                else {
+                    sourceIndex++;
+                }
+            }
+            if (modified) {
+                return source.flags & TypeFlags.Union ? getUnionType(sourceTypes, /*noSubtypeReduction*/ true) : getIntersectionType(sourceTypes);
+            }
+            return source;
+        }
+
         function getInferenceCandidates(context: InferenceContext, index: number): Type[] {
             let inferences = context.inferences[index];
             return inferences.primary || inferences.secondary || emptyArray;
@@ -7859,7 +7882,6 @@ namespace ts {
             return prop || unknownSymbol;
         }
 
-        let jsxElementClassType: Type = undefined;
         function getJsxGlobalElementClassType(): Type {
             if (!jsxElementClassType) {
                 jsxElementClassType = getExportedTypeFromNamespace(JsxNames.JSX, JsxNames.ElementClass);

tests/baselines/reference/genericSignatureIdentity.js

@@ -0,0 +1,32 @@
+//// [genericSignatureIdentity.ts]
+// This test is here to remind us of our current limits of type identity checking.
+// Ideally all of the below declarations would be considered different (and thus errors)
+// but they aren't because we erase type parameters to type any and don't check that
+// constraints are identical.
+
+var x: {
+    <T extends Date>(x: T): T;
+};
+
+var x: {
+    <T extends number>(x: T): T;
+};
+
+var x: {
+    <T>(x: T): T;
+};
+
+var x: {
+    <T>(x: any): any;
+};
+
+
+//// [genericSignatureIdentity.js]
+// This test is here to remind us of our current limits of type identity checking.
+// Ideally all of the below declarations would be considered different (and thus errors)
+// but they aren't because we erase type parameters to type any and don't check that
+// constraints are identical.
+var x;
+var x;
+var x;
+var x;

tests/baselines/reference/genericSignatureIdentity.symbols

@@ -0,0 +1,49 @@
+=== tests/cases/compiler/genericSignatureIdentity.ts ===
+// This test is here to remind us of our current limits of type identity checking.
+// Ideally all of the below declarations would be considered different (and thus errors)
+// but they aren't because we erase type parameters to type any and don't check that
+// constraints are identical.
+
+var x: {
+>x : Symbol(x, Decl(genericSignatureIdentity.ts, 5, 3), Decl(genericSignatureIdentity.ts, 9, 3), Decl(genericSignatureIdentity.ts, 13, 3), Decl(genericSignatureIdentity.ts, 17, 3))
+
+    <T extends Date>(x: T): T;
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 6, 5))
+>Date : Symbol(Date, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>x : Symbol(x, Decl(genericSignatureIdentity.ts, 6, 21))
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 6, 5))
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 6, 5))
+
+};
+
+var x: {
+>x : Symbol(x, Decl(genericSignatureIdentity.ts, 5, 3), Decl(genericSignatureIdentity.ts, 9, 3), Decl(genericSignatureIdentity.ts, 13, 3), Decl(genericSignatureIdentity.ts, 17, 3))
+
+    <T extends number>(x: T): T;
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 10, 5))
+>x : Symbol(x, Decl(genericSignatureIdentity.ts, 10, 23))
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 10, 5))
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 10, 5))
+
+};
+
+var x: {
+>x : Symbol(x, Decl(genericSignatureIdentity.ts, 5, 3), Decl(genericSignatureIdentity.ts, 9, 3), Decl(genericSignatureIdentity.ts, 13, 3), Decl(genericSignatureIdentity.ts, 17, 3))
+
+    <T>(x: T): T;
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 14, 5))
+>x : Symbol(x, Decl(genericSignatureIdentity.ts, 14, 8))
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 14, 5))
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 14, 5))
+
+};
+
+var x: {
+>x : Symbol(x, Decl(genericSignatureIdentity.ts, 5, 3), Decl(genericSignatureIdentity.ts, 9, 3), Decl(genericSignatureIdentity.ts, 13, 3), Decl(genericSignatureIdentity.ts, 17, 3))
+
+    <T>(x: any): any;
+>T : Symbol(T, Decl(genericSignatureIdentity.ts, 18, 5))
+>x : Symbol(x, Decl(genericSignatureIdentity.ts, 18, 8))
+
+};
+

tests/baselines/reference/genericSignatureIdentity.types

@@ -0,0 +1,49 @@
+=== tests/cases/compiler/genericSignatureIdentity.ts ===
+// This test is here to remind us of our current limits of type identity checking.
+// Ideally all of the below declarations would be considered different (and thus errors)
+// but they aren't because we erase type parameters to type any and don't check that
+// constraints are identical.
+
+var x: {
+>x : <T extends Date>(x: T) => T
+
+    <T extends Date>(x: T): T;
+>T : T
+>Date : Date
+>x : T
+>T : T
+>T : T
+
+};
+
+var x: {
+>x : <T extends Date>(x: T) => T
+
+    <T extends number>(x: T): T;
+>T : T
+>x : T
+>T : T
+>T : T
+
+};
+
+var x: {
+>x : <T extends Date>(x: T) => T
+
+    <T>(x: T): T;
+>T : T
+>x : T
+>T : T
+>T : T
+
+};
+
+var x: {
+>x : <T extends Date>(x: T) => T
+
+    <T>(x: any): any;
+>T : T
+>x : any
+
+};
+