Improve non-ambient class and function merge error

src/compiler/checker.ts

@@ -34034,13 +34034,22 @@ namespace ts {
                 });
             }
 
-            if (hasNonAmbientClass && !isConstructor && symbol.flags & SymbolFlags.Function) {
-                // A non-ambient class cannot be an implementation for a non-constructor function/class merge
-                // TODO: The below just replicates our older error from when classes and functions were
-                // entirely unable to merge - a more helpful message like "Class declaration cannot implement overload list"
-                // might be warranted. :shrug:
+            if (hasNonAmbientClass && !isConstructor && symbol.flags & SymbolFlags.Function && declarations) {
+                const relatedDiagnostics = filter(declarations, d => d.kind === SyntaxKind.ClassDeclaration)
+                    .map(d => createDiagnosticForNode(d, Diagnostics.Consider_adding_a_declare_modifier_to_this_class));
+
                 forEach(declarations, declaration => {
-                    addDuplicateDeclarationError(declaration, Diagnostics.Duplicate_identifier_0, symbolName(symbol), declarations);
+                    const diagnostic = declaration.kind === SyntaxKind.ClassDeclaration
+                            ? Diagnostics.Class_declaration_cannot_implement_overload_list_for_0
+                            : declaration.kind === SyntaxKind.FunctionDeclaration
+                                ? Diagnostics.Function_with_bodies_can_only_merge_with_classes_that_are_ambient
+                                : undefined;
+                    if (diagnostic) {
+                        addRelatedInfo(
+                            error(getNameOfDeclaration(declaration) || declaration, diagnostic, symbolName(symbol)),
+                            ...relatedDiagnostics
+                        );
+                    }
                 });
             }
 

src/compiler/diagnosticMessages.json

@@ -3336,6 +3336,14 @@
         "category": "Error",
         "code": 2812
     },
+    "Class declaration cannot implement overload list for '{0}'.": {
+        "category": "Error",
+        "code": 2813
+    },
+    "Function with bodies can only merge with classes that are ambient.": {
+        "category": "Error",
+        "code": 2814
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
@@ -5138,6 +5146,11 @@
         "category": "Message",
         "code": 6505
     },
+    "Consider adding a 'declare' modifier to this class.": {
+        "category": "Message",
+        "code": 6506
+    },
+
 
     "Include 'undefined' in index signature results": {
         "category": "Message",
@@ -5151,7 +5164,7 @@
         "category": "Message",
         "code": 6802
     },
-
+ 
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
         "code": 7005

tests/baselines/reference/augmentedTypesClass2a.errors.txt

@@ -1,7 +1,7 @@
 tests/cases/compiler/augmentedTypesClass2a.ts(2,7): error TS2300: Duplicate identifier 'c2'.
-tests/cases/compiler/augmentedTypesClass2a.ts(2,7): error TS2300: Duplicate identifier 'c2'.
-tests/cases/compiler/augmentedTypesClass2a.ts(3,10): error TS2300: Duplicate identifier 'c2'.
+tests/cases/compiler/augmentedTypesClass2a.ts(2,7): error TS2813: Class declaration cannot implement overload list for 'c2'.
 tests/cases/compiler/augmentedTypesClass2a.ts(3,10): error TS2300: Duplicate identifier 'c2'.
+tests/cases/compiler/augmentedTypesClass2a.ts(3,10): error TS2814: Function with bodies can only merge with classes that are ambient.
 tests/cases/compiler/augmentedTypesClass2a.ts(4,5): error TS2300: Duplicate identifier 'c2'.
 
 
@@ -10,15 +10,15 @@ tests/cases/compiler/augmentedTypesClass2a.ts(4,5): error TS2300: Duplicate iden
     class c2 { public foo() { } } // error
           ~~
 !!! error TS2300: Duplicate identifier 'c2'.
-!!! related TS6203 tests/cases/compiler/augmentedTypesClass2a.ts:3:10: 'c2' was also declared here.
           ~~
-!!! error TS2300: Duplicate identifier 'c2'.
+!!! error TS2813: Class declaration cannot implement overload list for 'c2'.
+!!! related TS6506 tests/cases/compiler/augmentedTypesClass2a.ts:2:7: Consider adding a 'declare' modifier to this class.
     function c2() { } // error
              ~~
 !!! error TS2300: Duplicate identifier 'c2'.
-!!! related TS6203 tests/cases/compiler/augmentedTypesClass2a.ts:2:7: 'c2' was also declared here.
              ~~
-!!! error TS2300: Duplicate identifier 'c2'.
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/augmentedTypesClass2a.ts:2:7: Consider adding a 'declare' modifier to this class.
     var c2 = () => { }
         ~~
 !!! error TS2300: Duplicate identifier 'c2'.

tests/baselines/reference/augmentedTypesFunction.errors.txt

@@ -4,10 +4,10 @@ tests/cases/compiler/augmentedTypesFunction.ts(6,10): error TS2393: Duplicate fu
 tests/cases/compiler/augmentedTypesFunction.ts(7,10): error TS2393: Duplicate function implementation.
 tests/cases/compiler/augmentedTypesFunction.ts(9,10): error TS2300: Duplicate identifier 'y2a'.
 tests/cases/compiler/augmentedTypesFunction.ts(10,5): error TS2300: Duplicate identifier 'y2a'.
-tests/cases/compiler/augmentedTypesFunction.ts(13,10): error TS2300: Duplicate identifier 'y3'.
-tests/cases/compiler/augmentedTypesFunction.ts(14,7): error TS2300: Duplicate identifier 'y3'.
-tests/cases/compiler/augmentedTypesFunction.ts(16,10): error TS2300: Duplicate identifier 'y3a'.
-tests/cases/compiler/augmentedTypesFunction.ts(17,7): error TS2300: Duplicate identifier 'y3a'.
+tests/cases/compiler/augmentedTypesFunction.ts(13,10): error TS2814: Function with bodies can only merge with classes that are ambient.
+tests/cases/compiler/augmentedTypesFunction.ts(14,7): error TS2813: Class declaration cannot implement overload list for 'y3'.
+tests/cases/compiler/augmentedTypesFunction.ts(16,10): error TS2814: Function with bodies can only merge with classes that are ambient.
+tests/cases/compiler/augmentedTypesFunction.ts(17,7): error TS2813: Class declaration cannot implement overload list for 'y3a'.
 tests/cases/compiler/augmentedTypesFunction.ts(20,10): error TS2567: Enum declarations can only merge with namespace or other enum declarations.
 tests/cases/compiler/augmentedTypesFunction.ts(21,6): error TS2567: Enum declarations can only merge with namespace or other enum declarations.
 
@@ -39,21 +39,21 @@ tests/cases/compiler/augmentedTypesFunction.ts(21,6): error TS2567: Enum declara
     // function then class
     function y3() { } // error
              ~~
-!!! error TS2300: Duplicate identifier 'y3'.
-!!! related TS6203 tests/cases/compiler/augmentedTypesFunction.ts:14:7: 'y3' was also declared here.
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/augmentedTypesFunction.ts:14:7: Consider adding a 'declare' modifier to this class.
     class y3 { } // error
           ~~
-!!! error TS2300: Duplicate identifier 'y3'.
-!!! related TS6203 tests/cases/compiler/augmentedTypesFunction.ts:13:10: 'y3' was also declared here.
+!!! error TS2813: Class declaration cannot implement overload list for 'y3'.
+!!! related TS6506 tests/cases/compiler/augmentedTypesFunction.ts:14:7: Consider adding a 'declare' modifier to this class.
 
     function y3a() { } // error
              ~~~
-!!! error TS2300: Duplicate identifier 'y3a'.
-!!! related TS6203 tests/cases/compiler/augmentedTypesFunction.ts:17:7: 'y3a' was also declared here.
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/augmentedTypesFunction.ts:17:7: Consider adding a 'declare' modifier to this class.
     class y3a { public foo() { } } // error
           ~~~
-!!! error TS2300: Duplicate identifier 'y3a'.
-!!! related TS6203 tests/cases/compiler/augmentedTypesFunction.ts:16:10: 'y3a' was also declared here.
+!!! error TS2813: Class declaration cannot implement overload list for 'y3a'.
+!!! related TS6506 tests/cases/compiler/augmentedTypesFunction.ts:17:7: Consider adding a 'declare' modifier to this class.
 
     // function then enum
     function y4() { } // error

tests/baselines/reference/callOverloads1.errors.txt

@@ -1,13 +1,13 @@
-tests/cases/compiler/callOverloads1.ts(1,7): error TS2300: Duplicate identifier 'Foo'.
-tests/cases/compiler/callOverloads1.ts(9,10): error TS2300: Duplicate identifier 'Foo'.
+tests/cases/compiler/callOverloads1.ts(1,7): error TS2813: Class declaration cannot implement overload list for 'Foo'.
 tests/cases/compiler/callOverloads1.ts(9,10): error TS2391: Function implementation is missing or not immediately following the declaration.
+tests/cases/compiler/callOverloads1.ts(9,10): error TS2814: Function with bodies can only merge with classes that are ambient.
 
 
 ==== tests/cases/compiler/callOverloads1.ts (3 errors) ====
     class Foo { // error
           ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads1.ts:9:10: 'Foo' was also declared here.
+!!! error TS2813: Class declaration cannot implement overload list for 'Foo'.
+!!! related TS6506 tests/cases/compiler/callOverloads1.ts:1:7: Consider adding a 'declare' modifier to this class.
         bar1() { /*WScript.Echo("bar1");*/ }
 
         constructor(x: any) {
@@ -17,10 +17,10 @@ tests/cases/compiler/callOverloads1.ts(9,10): error TS2391: Function implementat
 
     function Foo(); // error
              ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads1.ts:1:7: 'Foo' was also declared here.
-             ~~~
 !!! error TS2391: Function implementation is missing or not immediately following the declaration.
+             ~~~
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/callOverloads1.ts:1:7: Consider adding a 'declare' modifier to this class.
     function F1(s:string);
     function F1(a:any) { return a;}
 

tests/baselines/reference/callOverloads2.errors.txt

@@ -1,5 +1,5 @@
-tests/cases/compiler/callOverloads2.ts(1,7): error TS2300: Duplicate identifier 'Foo'.
-tests/cases/compiler/callOverloads2.ts(9,10): error TS2300: Duplicate identifier 'Foo'.
+tests/cases/compiler/callOverloads2.ts(1,7): error TS2813: Class declaration cannot implement overload list for 'Foo'.
+tests/cases/compiler/callOverloads2.ts(9,10): error TS2814: Function with bodies can only merge with classes that are ambient.
 tests/cases/compiler/callOverloads2.ts(11,10): error TS2389: Function implementation name must be 'Foo'.
 tests/cases/compiler/callOverloads2.ts(11,10): error TS2393: Duplicate function implementation.
 tests/cases/compiler/callOverloads2.ts(12,10): error TS2393: Duplicate function implementation.
@@ -9,8 +9,8 @@ tests/cases/compiler/callOverloads2.ts(14,10): error TS2391: Function implementa
 ==== tests/cases/compiler/callOverloads2.ts (6 errors) ====
     class Foo { // error
           ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads2.ts:9:10: 'Foo' was also declared here.
+!!! error TS2813: Class declaration cannot implement overload list for 'Foo'.
+!!! related TS6506 tests/cases/compiler/callOverloads2.ts:1:7: Consider adding a 'declare' modifier to this class.
         bar1() { /*WScript.Echo("bar1");*/ }
 
         constructor(x: any) {
@@ -20,8 +20,8 @@ tests/cases/compiler/callOverloads2.ts(14,10): error TS2391: Function implementa
 
     function Foo(); // error
              ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads2.ts:1:7: 'Foo' was also declared here.
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/callOverloads2.ts:1:7: Consider adding a 'declare' modifier to this class.
 
     function F1(s:string) {return s;} // error
              ~~

tests/baselines/reference/callOverloads3.errors.txt

@@ -1,27 +1,24 @@
-tests/cases/compiler/callOverloads3.ts(1,10): error TS2300: Duplicate identifier 'Foo'.
-tests/cases/compiler/callOverloads3.ts(2,10): error TS2300: Duplicate identifier 'Foo'.
+tests/cases/compiler/callOverloads3.ts(1,10): error TS2814: Function with bodies can only merge with classes that are ambient.
 tests/cases/compiler/callOverloads3.ts(2,10): error TS2391: Function implementation is missing or not immediately following the declaration.
-tests/cases/compiler/callOverloads3.ts(3,7): error TS2300: Duplicate identifier 'Foo'.
+tests/cases/compiler/callOverloads3.ts(2,10): error TS2814: Function with bodies can only merge with classes that are ambient.
+tests/cases/compiler/callOverloads3.ts(3,7): error TS2813: Class declaration cannot implement overload list for 'Foo'.
 
 
 ==== tests/cases/compiler/callOverloads3.ts (4 errors) ====
     function Foo():Foo; // error
              ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads3.ts:2:10: 'Foo' was also declared here.
-!!! related TS6204 tests/cases/compiler/callOverloads3.ts:3:7: and here.
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/callOverloads3.ts:3:7: Consider adding a 'declare' modifier to this class.
     function Foo(s:string):Foo; // error
              ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads3.ts:1:10: 'Foo' was also declared here.
-!!! related TS6204 tests/cases/compiler/callOverloads3.ts:3:7: and here.
-             ~~~
 !!! error TS2391: Function implementation is missing or not immediately following the declaration.
+             ~~~
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/callOverloads3.ts:3:7: Consider adding a 'declare' modifier to this class.
     class Foo { // error
           ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads3.ts:1:10: 'Foo' was also declared here.
-!!! related TS6204 tests/cases/compiler/callOverloads3.ts:2:10: and here.
+!!! error TS2813: Class declaration cannot implement overload list for 'Foo'.
+!!! related TS6506 tests/cases/compiler/callOverloads3.ts:3:7: Consider adding a 'declare' modifier to this class.
         bar1() { /*WScript.Echo("bar1");*/ }
         constructor(x: any) {
             // WScript.Echo("Constructor function has executed");

tests/baselines/reference/callOverloads4.errors.txt

@@ -1,27 +1,24 @@
-tests/cases/compiler/callOverloads4.ts(1,10): error TS2300: Duplicate identifier 'Foo'.
-tests/cases/compiler/callOverloads4.ts(2,10): error TS2300: Duplicate identifier 'Foo'.
+tests/cases/compiler/callOverloads4.ts(1,10): error TS2814: Function with bodies can only merge with classes that are ambient.
 tests/cases/compiler/callOverloads4.ts(2,10): error TS2391: Function implementation is missing or not immediately following the declaration.
-tests/cases/compiler/callOverloads4.ts(3,7): error TS2300: Duplicate identifier 'Foo'.
+tests/cases/compiler/callOverloads4.ts(2,10): error TS2814: Function with bodies can only merge with classes that are ambient.
+tests/cases/compiler/callOverloads4.ts(3,7): error TS2813: Class declaration cannot implement overload list for 'Foo'.
 
 
 ==== tests/cases/compiler/callOverloads4.ts (4 errors) ====
     function Foo():Foo; // error
              ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads4.ts:2:10: 'Foo' was also declared here.
-!!! related TS6204 tests/cases/compiler/callOverloads4.ts:3:7: and here.
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/callOverloads4.ts:3:7: Consider adding a 'declare' modifier to this class.
     function Foo(s:string):Foo; // error
              ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads4.ts:1:10: 'Foo' was also declared here.
-!!! related TS6204 tests/cases/compiler/callOverloads4.ts:3:7: and here.
-             ~~~
 !!! error TS2391: Function implementation is missing or not immediately following the declaration.
+             ~~~
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/callOverloads4.ts:3:7: Consider adding a 'declare' modifier to this class.
     class Foo { // error
           ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads4.ts:1:10: 'Foo' was also declared here.
-!!! related TS6204 tests/cases/compiler/callOverloads4.ts:2:10: and here.
+!!! error TS2813: Class declaration cannot implement overload list for 'Foo'.
+!!! related TS6506 tests/cases/compiler/callOverloads4.ts:3:7: Consider adding a 'declare' modifier to this class.
         bar1() { /*WScript.Echo("bar1");*/ }
         constructor(s: string);
         constructor(x: any) {

tests/baselines/reference/callOverloads5.errors.txt

@@ -1,27 +1,24 @@
-tests/cases/compiler/callOverloads5.ts(1,10): error TS2300: Duplicate identifier 'Foo'.
-tests/cases/compiler/callOverloads5.ts(2,10): error TS2300: Duplicate identifier 'Foo'.
+tests/cases/compiler/callOverloads5.ts(1,10): error TS2814: Function with bodies can only merge with classes that are ambient.
 tests/cases/compiler/callOverloads5.ts(2,10): error TS2391: Function implementation is missing or not immediately following the declaration.
-tests/cases/compiler/callOverloads5.ts(3,7): error TS2300: Duplicate identifier 'Foo'.
+tests/cases/compiler/callOverloads5.ts(2,10): error TS2814: Function with bodies can only merge with classes that are ambient.
+tests/cases/compiler/callOverloads5.ts(3,7): error TS2813: Class declaration cannot implement overload list for 'Foo'.
 
 
 ==== tests/cases/compiler/callOverloads5.ts (4 errors) ====
     function Foo():Foo; // error
              ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads5.ts:2:10: 'Foo' was also declared here.
-!!! related TS6204 tests/cases/compiler/callOverloads5.ts:3:7: and here.
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/callOverloads5.ts:3:7: Consider adding a 'declare' modifier to this class.
     function Foo(s:string):Foo; // error
              ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads5.ts:1:10: 'Foo' was also declared here.
-!!! related TS6204 tests/cases/compiler/callOverloads5.ts:3:7: and here.
-             ~~~
 !!! error TS2391: Function implementation is missing or not immediately following the declaration.
+             ~~~
+!!! error TS2814: Function with bodies can only merge with classes that are ambient.
+!!! related TS6506 tests/cases/compiler/callOverloads5.ts:3:7: Consider adding a 'declare' modifier to this class.
     class Foo { // error
           ~~~
-!!! error TS2300: Duplicate identifier 'Foo'.
-!!! related TS6203 tests/cases/compiler/callOverloads5.ts:1:10: 'Foo' was also declared here.
-!!! related TS6204 tests/cases/compiler/callOverloads5.ts:2:10: and here.
+!!! error TS2813: Class declaration cannot implement overload list for 'Foo'.
+!!! related TS6506 tests/cases/compiler/callOverloads5.ts:3:7: Consider adding a 'declare' modifier to this class.
     	bar1(s:string);
     	bar1(n:number);
         bar1(a:any) { /*WScript.Echo(a);*/ }