Merge pull request #5517 from Microsoft/comparableRelation

Introduce the "comparable" relation

src/compiler/checker.ts

@@ -5397,6 +5397,10 @@ namespace ts {
             return checkTypeAssignableTo(source, target, /*errorNode*/ undefined);
         }
 
+        /**
+         * This is *not* a bi-directional relationship.
+         * If one needs to check both directions for comparability, use a second call to this function or 'checkTypeComparableTo'.
+         */
         function isTypeComparableTo(source: Type, target: Type): boolean {
             return checkTypeComparableTo(source, target, /*errorNode*/ undefined);
         }
@@ -5409,6 +5413,10 @@ namespace ts {
             return checkTypeRelatedTo(source, target, assignableRelation, errorNode, headMessage, containingMessageChain);
         }
 
+        /**
+         * This is *not* a bi-directional relationship.
+         * If one needs to check both directions for comparability, use a second call to this function or 'isTypeComparableTo'.
+         */
         function checkTypeComparableTo(source: Type, target: Type, errorNode: Node, headMessage?: DiagnosticMessage, containingMessageChain?: DiagnosticMessageChain): boolean {
             return checkTypeRelatedTo(source, target, comparableRelation, errorNode, headMessage, containingMessageChain);
         }
@@ -5619,7 +5627,14 @@ namespace ts {
                     sourceType = typeToString(source, /*enclosingDeclaration*/ undefined, TypeFormatFlags.UseFullyQualifiedType);
                     targetType = typeToString(target, /*enclosingDeclaration*/ undefined, TypeFormatFlags.UseFullyQualifiedType);
                 }
-                reportError(message || Diagnostics.Type_0_is_not_assignable_to_type_1, sourceType, targetType);
+
+                if (!message) {
+                    message = relation === comparableRelation ?
+                        Diagnostics.Type_0_is_not_comparable_to_type_1 :
+                        Diagnostics.Type_0_is_not_assignable_to_type_1;
+                }
+
+                reportError(message, sourceType, targetType);
             }
 
             // Compare two types and return
@@ -5648,10 +5663,12 @@ namespace ts {
                     }
                 }
                 if (source.flags & TypeFlags.StringLiteral && target === stringType) return Ternary.True;
+
                 if (relation === assignableRelation || relation === comparableRelation) {
                     if (isTypeAny(source)) return Ternary.True;
                     if (source === numberType && target.flags & TypeFlags.Enum) return Ternary.True;
                 }
+
                 if (source.flags & TypeFlags.Boolean && target.flags & TypeFlags.Boolean) {
                     return Ternary.True;
                 }
@@ -5674,26 +5691,28 @@ namespace ts {
 
                 const saveErrorInfo = errorInfo;
 
-                // Note that the "each" checks must precede the "some" checks to produce the correct results
+                // Note that these checks are specifically ordered to produce correct results.
                 if (source.flags & TypeFlags.Union) {
                     if (relation === comparableRelation) {
-                        if (result = someTypeRelatedToType(<UnionType>source, target, reportErrors)) {
-                            return result;
-                        }
+                        result = someTypeRelatedToType(source as UnionType, target, reportErrors);
                     }
                     else {
-                        if (result = eachTypeRelatedToType(<UnionType>source, target, reportErrors)) {
-                            return result;
-                        }
+                        result = eachTypeRelatedToType(source as UnionType, target, reportErrors);
+                    }
+
+                    if (result) {
+                        return result;
                     }
                 }
                 else if (target.flags & TypeFlags.Intersection) {
-                    if (result = typeRelatedToEachType(source, <IntersectionType>target, reportErrors)) {
+                    result = typeRelatedToEachType(source, target as IntersectionType, reportErrors);
+
+                    if (result) {
                         return result;
                     }
                 }
                 else {
-                    // It is necessary to try "some" checks on both sides because there may be nested "each" checks
+                    // It is necessary to try these "some" checks on both sides because there may be nested "each" checks
                     // on either side that need to be prioritized. For example, A | B = (A | B) & (C | D) or
                     // A & B = (A & B) | (C & D).
                     if (source.flags & TypeFlags.Intersection) {
@@ -5775,8 +5794,8 @@ namespace ts {
                 }
                 if (source.flags & TypeFlags.Union && target.flags & TypeFlags.Union ||
                     source.flags & TypeFlags.Intersection && target.flags & TypeFlags.Intersection) {
-                    if (result = eachTypeRelatedToSomeType(<UnionOrIntersectionType>source, <UnionOrIntersectionType>target)) {
-                        if (result &= eachTypeRelatedToSomeType(<UnionOrIntersectionType>target, <UnionOrIntersectionType>source)) {
+                    if (result = eachTypeRelatedToSomeType(<UnionOrIntersectionType>source, <UnionOrIntersectionType>target, /*reportErrors*/ false)) {
+                        if (result &= eachTypeRelatedToSomeType(<UnionOrIntersectionType>target, <UnionOrIntersectionType>source, /*reportErrors*/ false)) {
                             return result;
                         }
                     }
@@ -5827,7 +5846,7 @@ namespace ts {
                 return false;
             }
 
-            function eachTypeRelatedToSomeType(source: UnionOrIntersectionType, target: UnionOrIntersectionType): Ternary {
+            function eachTypeRelatedToSomeType(source: UnionOrIntersectionType, target: UnionOrIntersectionType, reportErrors: boolean): Ternary {
                 let result = Ternary.True;
                 const sourceTypes = source.types;
                 for (const sourceType of sourceTypes) {
@@ -11015,7 +11034,7 @@ namespace ts {
             if (produceDiagnostics && targetType !== unknownType) {
                 const widenedType = getWidenedType(exprType);
                 if (!isTypeComparableTo(targetType, widenedType)) {
-                    checkTypeComparableTo(exprType, targetType, node, Diagnostics.Neither_type_0_nor_type_1_is_assignable_to_the_other);
+                    checkTypeComparableTo(exprType, targetType, node, Diagnostics.Type_0_cannot_be_converted_to_type_1);
                 }
             }
             return targetType;
@@ -14458,7 +14477,7 @@ namespace ts {
 
                 if (produceDiagnostics && clause.kind === SyntaxKind.CaseClause) {
                     const caseClause = <CaseClause>clause;
-                    // TypeScript 1.0 spec (April 2014):5.9
+                    // TypeScript 1.0 spec (April 2014): 5.9
                     // In a 'switch' statement, each 'case' expression must be of a type that is comparable
                     // to or from the type of the 'switch' expression.
                     const caseType = checkExpression(caseClause.expression);

src/compiler/diagnosticMessages.json

@@ -1047,7 +1047,7 @@
         "category": "Error",
         "code": 2351
     },
-    "Neither type '{0}' nor type '{1}' is assignable to the other.": {
+    "Type '{0}' cannot be converted to type '{1}'.": {
         "category": "Error",
         "code": 2352
     },
@@ -1875,6 +1875,10 @@
         "category": "Error",
         "code": 2677
     },
+    "Type '{0}' is not comparable to type '{1}'.": {
+        "category": "Error",
+        "code": 2678
+    },
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
         "code": 4000

tests/baselines/reference/arrayCast.errors.txt

@@ -1,5 +1,5 @@
-tests/cases/compiler/arrayCast.ts(3,23): error TS2352: Neither type '{ foo: string; }[]' nor type '{ id: number; }[]' is assignable to the other.
-  Type '{ foo: string; }' is not assignable to type '{ id: number; }'.
+tests/cases/compiler/arrayCast.ts(3,23): error TS2352: Type '{ foo: string; }[]' cannot be converted to type '{ id: number; }[]'.
+  Type '{ foo: string; }' is not comparable to type '{ id: number; }'.
     Object literal may only specify known properties, and 'foo' does not exist in type '{ id: number; }'.
 
 
@@ -8,8 +8,8 @@ tests/cases/compiler/arrayCast.ts(3,23): error TS2352: Neither type '{ foo: stri
     // has type { foo: string }[], which is not assignable to { id: number }[].
     <{ id: number; }[]>[{ foo: "s" }];
                           ~~~~~~~~
-!!! error TS2352: Neither type '{ foo: string; }[]' nor type '{ id: number; }[]' is assignable to the other.
-!!! error TS2352:   Type '{ foo: string; }' is not assignable to type '{ id: number; }'.
+!!! error TS2352: Type '{ foo: string; }[]' cannot be converted to type '{ id: number; }[]'.
+!!! error TS2352:   Type '{ foo: string; }' is not comparable to type '{ id: number; }'.
 !!! error TS2352:     Object literal may only specify known properties, and 'foo' does not exist in type '{ id: number; }'.
 
     // Should succeed, as the {} element causes the type of the array to be {}[]

tests/baselines/reference/asOperator2.errors.txt

@@ -1,8 +1,8 @@
-tests/cases/conformance/expressions/asOperator/asOperator2.ts(1,9): error TS2352: Neither type 'number' nor type 'string' is assignable to the other.
+tests/cases/conformance/expressions/asOperator/asOperator2.ts(1,9): error TS2352: Type 'number' cannot be converted to type 'string'.
 
 
 ==== tests/cases/conformance/expressions/asOperator/asOperator2.ts (1 errors) ====
     var x = 23 as string;
             ~~~~~~~~~~~~
-!!! error TS2352: Neither type 'number' nor type 'string' is assignable to the other.
+!!! error TS2352: Type 'number' cannot be converted to type 'string'.
 

tests/baselines/reference/asOperatorContextualType.errors.txt

@@ -1,10 +1,10 @@
-tests/cases/conformance/expressions/asOperator/asOperatorContextualType.ts(2,9): error TS2352: Neither type '(v: number) => number' nor type '(x: number) => string' is assignable to the other.
-  Type 'number' is not assignable to type 'string'.
+tests/cases/conformance/expressions/asOperator/asOperatorContextualType.ts(2,9): error TS2352: Type '(v: number) => number' cannot be converted to type '(x: number) => string'.
+  Type 'number' is not comparable to type 'string'.
 
 
 ==== tests/cases/conformance/expressions/asOperator/asOperatorContextualType.ts (1 errors) ====
     // should error
     var x = (v => v) as (x: number) => string;
             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2352: Neither type '(v: number) => number' nor type '(x: number) => string' is assignable to the other.
-!!! error TS2352:   Type 'number' is not assignable to type 'string'.
+!!! error TS2352: Type '(v: number) => number' cannot be converted to type '(x: number) => string'.
+!!! error TS2352:   Type 'number' is not comparable to type 'string'.

tests/baselines/reference/asOperatorNames.errors.txt

@@ -1,11 +1,11 @@
-tests/cases/conformance/expressions/asOperator/asOperatorNames.ts(2,9): error TS2352: Neither type 'number' nor type 'string' is assignable to the other.
+tests/cases/conformance/expressions/asOperator/asOperatorNames.ts(2,9): error TS2352: Type 'number' cannot be converted to type 'string'.
 
 
 ==== tests/cases/conformance/expressions/asOperator/asOperatorNames.ts (1 errors) ====
     var a = 20;
     var b = a as string;
             ~~~~~~~~~~~
-!!! error TS2352: Neither type 'number' nor type 'string' is assignable to the other.
+!!! error TS2352: Type 'number' cannot be converted to type 'string'.
     var as = "hello";
     var as1 = as as string;
 

tests/baselines/reference/castingTuple.errors.txt

@@ -1,9 +1,9 @@
-tests/cases/conformance/types/tuple/castingTuple.ts(28,10): error TS2352: Neither type '[number, string]' nor type '[number, number]' is assignable to the other.
+tests/cases/conformance/types/tuple/castingTuple.ts(28,10): error TS2352: Type '[number, string]' cannot be converted to type '[number, number]'.
   Types of property '1' are incompatible.
-    Type 'string' is not assignable to type 'number'.
-tests/cases/conformance/types/tuple/castingTuple.ts(29,10): error TS2352: Neither type '[C, D]' nor type '[A, I]' is assignable to the other.
+    Type 'string' is not comparable to type 'number'.
+tests/cases/conformance/types/tuple/castingTuple.ts(29,10): error TS2352: Type '[C, D]' cannot be converted to type '[A, I]'.
   Types of property '0' are incompatible.
-    Type 'C' is not assignable to type 'A'.
+    Type 'C' is not comparable to type 'A'.
       Property 'a' is missing in type 'C'.
 tests/cases/conformance/types/tuple/castingTuple.ts(30,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'array1' must be of type '{}[]', but here has type 'number[]'.
 tests/cases/conformance/types/tuple/castingTuple.ts(31,1): error TS2304: Cannot find name 't4'.
@@ -39,14 +39,14 @@ tests/cases/conformance/types/tuple/castingTuple.ts(31,1): error TS2304: Cannot
     // error
     var t3 = <[number, number]>numStrTuple;
              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2352: Neither type '[number, string]' nor type '[number, number]' is assignable to the other.
+!!! error TS2352: Type '[number, string]' cannot be converted to type '[number, number]'.
 !!! error TS2352:   Types of property '1' are incompatible.
-!!! error TS2352:     Type 'string' is not assignable to type 'number'.
+!!! error TS2352:     Type 'string' is not comparable to type 'number'.
     var t9 = <[A, I]>classCDTuple;
              ~~~~~~~~~~~~~~~~~~~~
-!!! error TS2352: Neither type '[C, D]' nor type '[A, I]' is assignable to the other.
+!!! error TS2352: Type '[C, D]' cannot be converted to type '[A, I]'.
 !!! error TS2352:   Types of property '0' are incompatible.
-!!! error TS2352:     Type 'C' is not assignable to type 'A'.
+!!! error TS2352:     Type 'C' is not comparable to type 'A'.
 !!! error TS2352:       Property 'a' is missing in type 'C'.
     var array1 = <number[]>numStrTuple;
         ~~~~~~

tests/baselines/reference/contextualTyping39.errors.txt

@@ -1,9 +1,9 @@
-tests/cases/compiler/contextualTyping39.ts(1,11): error TS2352: Neither type '() => string' nor type '() => number' is assignable to the other.
-  Type 'string' is not assignable to type 'number'.
+tests/cases/compiler/contextualTyping39.ts(1,11): error TS2352: Type '() => string' cannot be converted to type '() => number'.
+  Type 'string' is not comparable to type 'number'.
 
 
 ==== tests/cases/compiler/contextualTyping39.ts (1 errors) ====
     var foo = <{ (): number; }> function() { return "err"; };
               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2352: Neither type '() => string' nor type '() => number' is assignable to the other.
-!!! error TS2352:   Type 'string' is not assignable to type 'number'.
+!!! error TS2352: Type '() => string' cannot be converted to type '() => number'.
+!!! error TS2352:   Type 'string' is not comparable to type 'number'.

tests/baselines/reference/contextualTyping41.errors.txt

@@ -1,9 +1,9 @@
-tests/cases/compiler/contextualTyping41.ts(1,11): error TS2352: Neither type '() => string' nor type '{ (): number; (i: number): number; }' is assignable to the other.
-  Type 'string' is not assignable to type 'number'.
+tests/cases/compiler/contextualTyping41.ts(1,11): error TS2352: Type '() => string' cannot be converted to type '{ (): number; (i: number): number; }'.
+  Type 'string' is not comparable to type 'number'.
 
 
 ==== tests/cases/compiler/contextualTyping41.ts (1 errors) ====
     var foo = <{():number; (i:number):number; }> (function(){return "err";});
               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2352: Neither type '() => string' nor type '{ (): number; (i: number): number; }' is assignable to the other.
-!!! error TS2352:   Type 'string' is not assignable to type 'number'.
+!!! error TS2352: Type '() => string' cannot be converted to type '{ (): number; (i: number): number; }'.
+!!! error TS2352:   Type 'string' is not comparable to type 'number'.

tests/baselines/reference/defaultArgsInFunctionExpressions.errors.txt

@@ -2,9 +2,9 @@ tests/cases/compiler/defaultArgsInFunctionExpressions.ts(4,19): error TS2345: Ar
 tests/cases/compiler/defaultArgsInFunctionExpressions.ts(5,1): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/compiler/defaultArgsInFunctionExpressions.ts(8,20): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/compiler/defaultArgsInFunctionExpressions.ts(11,1): error TS2322: Type 'string' is not assignable to type 'number'.
-tests/cases/compiler/defaultArgsInFunctionExpressions.ts(14,51): error TS2352: Neither type 'string' nor type 'number' is assignable to the other.
+tests/cases/compiler/defaultArgsInFunctionExpressions.ts(14,51): error TS2352: Type 'string' cannot be converted to type 'number'.
 tests/cases/compiler/defaultArgsInFunctionExpressions.ts(17,41): error TS2322: Type 'string' is not assignable to type 'number'.
-tests/cases/compiler/defaultArgsInFunctionExpressions.ts(20,62): error TS2352: Neither type 'string' nor type 'number' is assignable to the other.
+tests/cases/compiler/defaultArgsInFunctionExpressions.ts(20,62): error TS2352: Type 'string' cannot be converted to type 'number'.
 tests/cases/compiler/defaultArgsInFunctionExpressions.ts(28,15): error TS2304: Cannot find name 'T'.
 
 
@@ -32,7 +32,7 @@ tests/cases/compiler/defaultArgsInFunctionExpressions.ts(28,15): error TS2304: C
     // Contextually type the default arg with the type annotation
     var f3 = function (a: (s: string) => any = (s) => <number>s) { };
                                                       ~~~~~~~~~
-!!! error TS2352: Neither type 'string' nor type 'number' is assignable to the other.
+!!! error TS2352: Type 'string' cannot be converted to type 'number'.
 
     // Type check using the function's contextual type
     var f4: (a: number) => void = function (a = "") { };
@@ -42,7 +42,7 @@ tests/cases/compiler/defaultArgsInFunctionExpressions.ts(28,15): error TS2304: C
     // Contextually type the default arg using the function's contextual type
     var f5: (a: (s: string) => any) => void = function (a = s => <number>s) { };
                                                                  ~~~~~~~~~
-!!! error TS2352: Neither type 'string' nor type 'number' is assignable to the other.
+!!! error TS2352: Type 'string' cannot be converted to type 'number'.
 
     // Instantiated module
     module T { }