improvements based on comments

.gitignore

@@ -44,3 +44,4 @@ internal/
 .settings
 .vscode/*
 !.vscode/tasks.json
+.idea

src/compiler/checker.ts

@@ -3854,6 +3854,11 @@ namespace ts {
             return false;
         }
 
+        function typeHasCallSignatures(type: Type): boolean {
+            const callSignature = getSignaturesOfType(type, SignatureKind.Call);
+            return !!callSignature.length;
+        }
+
         function typeHasCallOrConstructSignatures(type: Type): boolean {
             const apparentType = getApparentType(type);
             if (apparentType.flags & TypeFlags.StructuredType) {
@@ -9496,7 +9501,7 @@ namespace ts {
                     error(node, Diagnostics.Value_of_type_0_is_not_callable_Did_you_mean_to_include_new, typeToString(funcType));
                 }
                 else {
-                    error(node, Diagnostics.Cannot_invoke_an_expression_whose_type_lacks_a_call_signature);
+                    error(node, Diagnostics.Cannot_invoke_an_expression_whose_type_lacks_a_call_signature_Type_0_has_no_compatible_call_signatures, typeToString(apparentType));
                 }
                 return resolveErrorCall(node);
             }
@@ -9586,7 +9591,7 @@ namespace ts {
             }
 
             if (!callSignatures.length) {
-                error(node, Diagnostics.Cannot_invoke_an_expression_whose_type_lacks_a_call_signature);
+                error(node, Diagnostics.Cannot_invoke_an_expression_whose_type_lacks_a_call_signature_Type_0_has_no_compatible_call_signatures, typeToString(apparentType));
                 return resolveErrorCall(node);
             }
 
@@ -9633,7 +9638,7 @@ namespace ts {
             const headMessage = getDiagnosticHeadMessageForDecoratorResolution(node);
             if (!callSignatures.length) {
                 let errorInfo: DiagnosticMessageChain;
-                errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.Cannot_invoke_an_expression_whose_type_lacks_a_call_signature);
+                errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.Cannot_invoke_an_expression_whose_type_lacks_a_call_signature_Type_0_has_no_compatible_call_signatures, typeToString(apparentType));
                 errorInfo = chainDiagnosticMessages(errorInfo, headMessage);
                 diagnostics.add(createDiagnosticForNodeFromMessageChain(node, errorInfo));
                 return resolveErrorCall(node);

tests/cases/conformance/types/union/unionTypeCallSignatures.ts

@@ -16,9 +16,9 @@ unionOfDifferentReturnType1(true); // error in type of parameter
 unionOfDifferentReturnType1(); // error missing parameter
 
 var unionOfDifferentParameterTypes: { (a: number): number; } | { (a: string): Date; };
-unionOfDifferentParameterTypes(10); //no error
-unionOfDifferentParameterTypes("hello"); //no error
-unionOfDifferentParameterTypes();  //error TS2346
+unionOfDifferentParameterTypes(10);// error - no call signatures
+unionOfDifferentParameterTypes("hello");// error - no call signatures
+unionOfDifferentParameterTypes();// error - no call signatures
 
 var unionOfDifferentNumberOfSignatures: { (a: number): number; } | { (a: number): Date; (a: string): boolean; };
 unionOfDifferentNumberOfSignatures(); // error - no call signatures
@@ -26,9 +26,9 @@ unionOfDifferentNumberOfSignatures(10); // error - no call signatures
 unionOfDifferentNumberOfSignatures("hello"); // error - no call signatures
 
 var unionWithDifferentParameterCount: { (a: string): string; } | { (a: string, b: number): number; } ;
-unionWithDifferentParameterCount();  //error TS2346
-unionWithDifferentParameterCount("hello"); //no error
-unionWithDifferentParameterCount("hello", 10); //no error
+unionWithDifferentParameterCount();// no  call signature
+unionWithDifferentParameterCount("hello");// no  call signature
+unionWithDifferentParameterCount("hello", 10);// no  call signature
 
 var unionWithOptionalParameter1: { (a: string, b?: number): string; } | { (a: string, b?: number): number; };
 strOrNum = unionWithOptionalParameter1('hello');
@@ -71,4 +71,4 @@ strOrNum = unionWithRestParameter3(); // error no call signature
 
 var unionWithRestParameter4: { (...a: string[]): string; } | { (a: string, b: string): number; };
 strOrNum = unionWithRestParameter4("hello"); // error supplied parameters do not match any call signature
-strOrNum = unionWithRestParameter4("hello", "world");
+strOrNum = unionWithRestParameter4("hello", "world");

tests/cases/conformance/types/union/unionTypeCallSignatures5.ts

@@ -1,12 +0,0 @@
-interface A {
-    (number) : number;
-}
-
-var f1: string | number;
-f1(); //error TS2658
-
-var f2: string | A;
-f2(); //error TS2658
-
-var f3: string[] | number[];
-f3.map(value=>value); //should not throw TS2349

tests/cases/conformance/types/union/unionTypeMembers.ts

@@ -41,7 +41,8 @@ str = x.commonMethodType(str); // (a: string) => string so result should be stri
 strOrNum = x.commonPropertyDifferenType;
 strOrNum = x.commonMethodDifferentReturnType(str); // string | union
 x.commonMethodDifferentParameterType; // No error - property exists
-x.commonMethodDifferentParameterType(strOrNum); //error - TS2345
+x.commonMethodDifferentParameterType(strOrNum); // error - no call signatures because the type of this property is ((a: string) => string) | (a: number) => number
+                                                // and the call signatures arent identical
 num = x.commonMethodWithTypeParameter(num);
 num = x.commonMethodWithOwnTypeParameter(num);
 str = x.commonMethodWithOwnTypeParameter(str);