Change assignability to account for type parameters extending unions

src/compiler/checker.ts

@@ -4016,6 +4016,7 @@ module ts {
                         if (source === numberType && target.flags & TypeFlags.Enum) return Ternary.True;
                     }
                 }
+                let saveErrorInfo = errorInfo;
                 if (source.flags & TypeFlags.Union || target.flags & TypeFlags.Union) {
                     if (relation === identityRelation) {
                         if (source.flags & TypeFlags.Union && target.flags & TypeFlags.Union) {
@@ -4054,25 +4055,34 @@ module ts {
                         return result;
                     }
                 }
-                else {
-                    let saveErrorInfo = errorInfo;
-                    if (source.flags & TypeFlags.Reference && target.flags & TypeFlags.Reference && (<TypeReference>source).target === (<TypeReference>target).target) {
-                        // We have type references to same target type, see if relationship holds for all type arguments
-                        if (result = typesRelatedTo((<TypeReference>source).typeArguments, (<TypeReference>target).typeArguments, reportErrors)) {
-                            return result;
-                        }
+                else if (source.flags & TypeFlags.Reference && target.flags & TypeFlags.Reference && (<TypeReference>source).target === (<TypeReference>target).target) {
+                    // We have type references to same target type, see if relationship holds for all type arguments
+                    if (result = typesRelatedTo((<TypeReference>source).typeArguments, (<TypeReference>target).typeArguments, reportErrors)) {
+                        return result;
                     }
-                    // Even if relationship doesn't hold for type arguments, it may hold in a structural comparison
-                    // Report structural errors only if we haven't reported any errors yet
-                    let reportStructuralErrors = reportErrors && errorInfo === saveErrorInfo;
-                    // identity relation does not use apparent type
-                    let sourceOrApparentType = relation === identityRelation ? source : getApparentType(source);
-                    if (sourceOrApparentType.flags & TypeFlags.ObjectType && target.flags & TypeFlags.ObjectType &&
-                        (result = objectTypeRelatedTo(sourceOrApparentType, <ObjectType>target, reportStructuralErrors))) {
+                }
+
+                // Even if relationship doesn't hold for unions, type parameters, or generic type references,
+                // it may hold in a structural comparison.
+                // Report structural errors only if we haven't reported any errors yet
+                let reportStructuralErrors = reportErrors && errorInfo === saveErrorInfo;
+                // identity relation does not use apparent type
+                let sourceOrApparentType = relation === identityRelation ? source : getApparentType(source);
+                if (sourceOrApparentType.flags & TypeFlags.ObjectType && target.flags & TypeFlags.ObjectType) {
+                    if (result = objectTypeRelatedTo(sourceOrApparentType, <ObjectType>target, reportStructuralErrors)) {
                         errorInfo = saveErrorInfo;
                         return result;
                     }
                 }
+                else if (source.flags & TypeFlags.TypeParameter && sourceOrApparentType.flags & TypeFlags.Union) {
+                    // We clear the errors first because the following check often gives a better error than
+                    // the union comparison above if it is applicable.
+                    errorInfo = saveErrorInfo;
+                    if (result = isRelatedTo(sourceOrApparentType, target, reportErrors)) {
+                        return result;
+                    }
+                }
+
                 if (reportErrors) {
                     headMessage = headMessage || Diagnostics.Type_0_is_not_assignable_to_type_1;
                     let sourceType = typeToString(source);

tests/baselines/reference/typeParameterDiamond1.js

@@ -0,0 +1,28 @@
+//// [typeParameterDiamond1.ts]
+function diamondTop<Top>() {
+    function diamondMiddle<T extends Top, U extends Top>() {
+        function diamondBottom<Bottom extends T | U>() {
+            var top: Top;
+            var middle: T | U;
+            var bottom: Bottom;
+
+            top = middle;
+            middle = bottom;
+            top = bottom;
+        }
+    }
+}
+
+//// [typeParameterDiamond1.js]
+function diamondTop() {
+    function diamondMiddle() {
+        function diamondBottom() {
+            var top;
+            var middle;
+            var bottom;
+            top = middle;
+            middle = bottom;
+            top = bottom;
+        }
+    }
+}

tests/baselines/reference/typeParameterDiamond1.types

@@ -0,0 +1,48 @@
+=== tests/cases/compiler/typeParameterDiamond1.ts ===
+function diamondTop<Top>() {
+>diamondTop : <Top>() => void, Symbol(diamondTop, Decl(typeParameterDiamond1.ts, 0, 0))
+>Top : Top, Symbol(Top, Decl(typeParameterDiamond1.ts, 0, 20))
+
+    function diamondMiddle<T extends Top, U extends Top>() {
+>diamondMiddle : <T extends Top, U extends Top>() => void, Symbol(diamondMiddle, Decl(typeParameterDiamond1.ts, 0, 28))
+>T : T, Symbol(T, Decl(typeParameterDiamond1.ts, 1, 27))
+>Top : Top, Symbol(Top, Decl(typeParameterDiamond1.ts, 0, 20))
+>U : U, Symbol(U, Decl(typeParameterDiamond1.ts, 1, 41))
+>Top : Top, Symbol(Top, Decl(typeParameterDiamond1.ts, 0, 20))
+
+        function diamondBottom<Bottom extends T | U>() {
+>diamondBottom : <Bottom extends T | U>() => void, Symbol(diamondBottom, Decl(typeParameterDiamond1.ts, 1, 60))
+>Bottom : Bottom, Symbol(Bottom, Decl(typeParameterDiamond1.ts, 2, 31))
+>T : T, Symbol(T, Decl(typeParameterDiamond1.ts, 1, 27))
+>U : U, Symbol(U, Decl(typeParameterDiamond1.ts, 1, 41))
+
+            var top: Top;
+>top : Top, Symbol(top, Decl(typeParameterDiamond1.ts, 3, 15))
+>Top : Top, Symbol(Top, Decl(typeParameterDiamond1.ts, 0, 20))
+
+            var middle: T | U;
+>middle : T | U, Symbol(middle, Decl(typeParameterDiamond1.ts, 4, 15))
+>T : T, Symbol(T, Decl(typeParameterDiamond1.ts, 1, 27))
+>U : U, Symbol(U, Decl(typeParameterDiamond1.ts, 1, 41))
+
+            var bottom: Bottom;
+>bottom : Bottom, Symbol(bottom, Decl(typeParameterDiamond1.ts, 5, 15))
+>Bottom : Bottom, Symbol(Bottom, Decl(typeParameterDiamond1.ts, 2, 31))
+
+            top = middle;
+>top = middle : T | U
+>top : Top, Symbol(top, Decl(typeParameterDiamond1.ts, 3, 15))
+>middle : T | U, Symbol(middle, Decl(typeParameterDiamond1.ts, 4, 15))
+
+            middle = bottom;
+>middle = bottom : Bottom
+>middle : T | U, Symbol(middle, Decl(typeParameterDiamond1.ts, 4, 15))
+>bottom : Bottom, Symbol(bottom, Decl(typeParameterDiamond1.ts, 5, 15))
+
+            top = bottom;
+>top = bottom : Bottom
+>top : Top, Symbol(top, Decl(typeParameterDiamond1.ts, 3, 15))
+>bottom : Bottom, Symbol(bottom, Decl(typeParameterDiamond1.ts, 5, 15))
+        }
+    }
+}

tests/baselines/reference/typeParameterDiamond2.errors.txt

@@ -0,0 +1,28 @@
+tests/cases/compiler/typeParameterDiamond2.ts(8,13): error TS2322: Type 'T | U' is not assignable to type 'Top'.
+  Type 'U' is not assignable to type 'Top'.
+tests/cases/compiler/typeParameterDiamond2.ts(10,13): error TS2322: Type 'Bottom' is not assignable to type 'Top'.
+  Type 'T | U' is not assignable to type 'Top'.
+    Type 'U' is not assignable to type 'Top'.
+
+
+==== tests/cases/compiler/typeParameterDiamond2.ts (2 errors) ====
+    function diamondTop<Top>() {
+        function diamondMiddle<T extends Top, U>() {
+            function diamondBottom<Bottom extends T | U>() {
+                var top: Top;
+                var middle: T | U;
+                var bottom: Bottom;
+
+                top = middle;
+                ~~~
+!!! error TS2322: Type 'T | U' is not assignable to type 'Top'.
+!!! error TS2322:   Type 'U' is not assignable to type 'Top'.
+                middle = bottom;
+                top = bottom;
+                ~~~
+!!! error TS2322: Type 'Bottom' is not assignable to type 'Top'.
+!!! error TS2322:   Type 'T | U' is not assignable to type 'Top'.
+!!! error TS2322:     Type 'U' is not assignable to type 'Top'.
+            }
+        }
+    }

tests/baselines/reference/typeParameterDiamond2.js

@@ -0,0 +1,28 @@
+//// [typeParameterDiamond2.ts]
+function diamondTop<Top>() {
+    function diamondMiddle<T extends Top, U>() {
+        function diamondBottom<Bottom extends T | U>() {
+            var top: Top;
+            var middle: T | U;
+            var bottom: Bottom;
+
+            top = middle;
+            middle = bottom;
+            top = bottom;
+        }
+    }
+}
+
+//// [typeParameterDiamond2.js]
+function diamondTop() {
+    function diamondMiddle() {
+        function diamondBottom() {
+            var top;
+            var middle;
+            var bottom;
+            top = middle;
+            middle = bottom;
+            top = bottom;
+        }
+    }
+}

tests/baselines/reference/typeParameterDiamond3.errors.txt

@@ -0,0 +1,37 @@
+tests/cases/compiler/typeParameterDiamond3.ts(8,13): error TS2322: Type 'T | U' is not assignable to type 'Top'.
+  Type 'T' is not assignable to type 'Top'.
+tests/cases/compiler/typeParameterDiamond3.ts(9,13): error TS2322: Type 'Bottom' is not assignable to type 'T | U'.
+  Type 'Top | T | U' is not assignable to type 'T | U'.
+    Type 'Top' is not assignable to type 'T | U'.
+      Type 'Top' is not assignable to type 'U'.
+tests/cases/compiler/typeParameterDiamond3.ts(10,13): error TS2322: Type 'Bottom' is not assignable to type 'Top'.
+  Type 'Top | T | U' is not assignable to type 'Top'.
+    Type 'T' is not assignable to type 'Top'.
+
+
+==== tests/cases/compiler/typeParameterDiamond3.ts (3 errors) ====
+    function diamondTop<Top>() {
+        function diamondMiddle<T, U>() {
+            function diamondBottom<Bottom extends Top | T | U>() {
+                var top: Top;
+                var middle: T | U;
+                var bottom: Bottom;
+
+                top = middle;
+                ~~~
+!!! error TS2322: Type 'T | U' is not assignable to type 'Top'.
+!!! error TS2322:   Type 'T' is not assignable to type 'Top'.
+                middle = bottom;
+                ~~~~~~
+!!! error TS2322: Type 'Bottom' is not assignable to type 'T | U'.
+!!! error TS2322:   Type 'Top | T | U' is not assignable to type 'T | U'.
+!!! error TS2322:     Type 'Top' is not assignable to type 'T | U'.
+!!! error TS2322:       Type 'Top' is not assignable to type 'U'.
+                top = bottom;
+                ~~~
+!!! error TS2322: Type 'Bottom' is not assignable to type 'Top'.
+!!! error TS2322:   Type 'Top | T | U' is not assignable to type 'Top'.
+!!! error TS2322:     Type 'T' is not assignable to type 'Top'.
+            }
+        }
+    }

tests/baselines/reference/typeParameterDiamond3.js

@@ -0,0 +1,28 @@
+//// [typeParameterDiamond3.ts]
+function diamondTop<Top>() {
+    function diamondMiddle<T, U>() {
+        function diamondBottom<Bottom extends Top | T | U>() {
+            var top: Top;
+            var middle: T | U;
+            var bottom: Bottom;
+
+            top = middle;
+            middle = bottom;
+            top = bottom;
+        }
+    }
+}
+
+//// [typeParameterDiamond3.js]
+function diamondTop() {
+    function diamondMiddle() {
+        function diamondBottom() {
+            var top;
+            var middle;
+            var bottom;
+            top = middle;
+            middle = bottom;
+            top = bottom;
+        }
+    }
+}

tests/baselines/reference/typeParameterDiamond4.errors.txt

@@ -0,0 +1,28 @@
+tests/cases/compiler/typeParameterDiamond4.ts(8,13): error TS2322: Type 'Top | T | U' is not assignable to type 'Top'.
+  Type 'T' is not assignable to type 'Top'.
+tests/cases/compiler/typeParameterDiamond4.ts(10,13): error TS2322: Type 'Bottom' is not assignable to type 'Top'.
+  Type 'Top | T | U' is not assignable to type 'Top'.
+    Type 'T' is not assignable to type 'Top'.
+
+
+==== tests/cases/compiler/typeParameterDiamond4.ts (2 errors) ====
+    function diamondTop<Top>() {
+        function diamondMiddle<T, U>() {
+            function diamondBottom<Bottom extends Top | T | U>() {
+                var top: Top;
+                var middle: Top | T | U;
+                var bottom: Bottom;
+
+                top = middle;
+                ~~~
+!!! error TS2322: Type 'Top | T | U' is not assignable to type 'Top'.
+!!! error TS2322:   Type 'T' is not assignable to type 'Top'.
+                middle = bottom;
+                top = bottom;
+                ~~~
+!!! error TS2322: Type 'Bottom' is not assignable to type 'Top'.
+!!! error TS2322:   Type 'Top | T | U' is not assignable to type 'Top'.
+!!! error TS2322:     Type 'T' is not assignable to type 'Top'.
+            }
+        }
+    }

tests/baselines/reference/typeParameterDiamond4.js

@@ -0,0 +1,28 @@
+//// [typeParameterDiamond4.ts]
+function diamondTop<Top>() {
+    function diamondMiddle<T, U>() {
+        function diamondBottom<Bottom extends Top | T | U>() {
+            var top: Top;
+            var middle: Top | T | U;
+            var bottom: Bottom;
+
+            top = middle;
+            middle = bottom;
+            top = bottom;
+        }
+    }
+}
+
+//// [typeParameterDiamond4.js]
+function diamondTop() {
+    function diamondMiddle() {
+        function diamondBottom() {
+            var top;
+            var middle;
+            var bottom;
+            top = middle;
+            middle = bottom;
+            top = bottom;
+        }
+    }
+}

tests/baselines/reference/typeParameterExtendingUnion1.js

@@ -0,0 +1,48 @@
+//// [typeParameterExtendingUnion1.ts]
+class Animal { run() { } }
+class Cat extends Animal { meow }
+class Dog extends Animal { woof }
+
+function run(a: Animal) {
+    a.run();
+}
+
+function f<T extends Cat | Dog>(a: T) {
+    a.run();
+    run(a);
+}
+
+//// [typeParameterExtendingUnion1.js]
+var __extends = this.__extends || function (d, b) {
+    for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
+    function __() { this.constructor = d; }
+    __.prototype = b.prototype;
+    d.prototype = new __();
+};
+var Animal = (function () {
+    function Animal() {
+    }
+    Animal.prototype.run = function () { };
+    return Animal;
+})();
+var Cat = (function (_super) {
+    __extends(Cat, _super);
+    function Cat() {
+        _super.apply(this, arguments);
+    }
+    return Cat;
+})(Animal);
+var Dog = (function (_super) {
+    __extends(Dog, _super);
+    function Dog() {
+        _super.apply(this, arguments);
+    }
+    return Dog;
+})(Animal);
+function run(a) {
+    a.run();
+}
+function f(a) {
+    a.run();
+    run(a);
+}