Properly determine whether an augmentation is a ValueModule or NamespaceModule

src/compiler/binder.ts

@@ -1512,7 +1512,7 @@ namespace ts {
                     errorOnFirstToken(node, Diagnostics.export_modifier_cannot_be_applied_to_ambient_modules_and_module_augmentations_since_they_are_always_visible);
                 }
                 if (isExternalModuleAugmentation(node)) {
-                    declareSymbolAndAddToSymbolTable(node, SymbolFlags.NamespaceModule, SymbolFlags.NamespaceModuleExcludes);
+                    declareModuleSymbol(node);
                 }
                 else {
                     let pattern: Pattern | undefined;
@@ -1534,12 +1534,8 @@ namespace ts {
                 }
             }
             else {
-                const state = getModuleInstanceState(node);
-                if (state === ModuleInstanceState.NonInstantiated) {
-                    declareSymbolAndAddToSymbolTable(node, SymbolFlags.NamespaceModule, SymbolFlags.NamespaceModuleExcludes);
-                }
-                else {
-                    declareSymbolAndAddToSymbolTable(node, SymbolFlags.ValueModule, SymbolFlags.ValueModuleExcludes);
+                const state = declareModuleSymbol(node);
+                if (state !== ModuleInstanceState.NonInstantiated) {
                     if (node.symbol.flags & (SymbolFlags.Function | SymbolFlags.Class | SymbolFlags.RegularEnum)) {
                         // if module was already merged with some function, class or non-const enum
                         // treat is a non-const-enum-only
@@ -1560,6 +1556,15 @@ namespace ts {
             }
         }
 
+        function declareModuleSymbol(node: ModuleDeclaration): ModuleInstanceState {
+            const state = getModuleInstanceState(node);
+            const instantiated = state !== ModuleInstanceState.NonInstantiated;
+            declareSymbolAndAddToSymbolTable(node,
+                instantiated ? SymbolFlags.ValueModule : SymbolFlags.NamespaceModule,
+                instantiated ? SymbolFlags.ValueModuleExcludes : SymbolFlags.NamespaceModuleExcludes);
+            return state;
+        }
+
         function bindFunctionOrConstructorType(node: SignatureDeclaration): void {
             // For a given function symbol "<...>(...) => T" we want to generate a symbol identical
             // to the one we would get for: { <...>(...): T }

src/compiler/checker.ts

@@ -486,6 +486,9 @@ namespace ts {
                 }
                 recordMergedSymbol(target, source);
             }
+            else if (target.flags & SymbolFlags.NamespaceModule) {
+                error(source.valueDeclaration.name, Diagnostics.Cannot_augment_module_0_with_value_exports_because_it_resolves_to_a_non_module_entity, symbolToString(target));
+            }
             else {
                 const message = target.flags & SymbolFlags.BlockScopedVariable || source.flags & SymbolFlags.BlockScopedVariable
                     ? Diagnostics.Cannot_redeclare_block_scoped_variable_0 : Diagnostics.Duplicate_identifier_0;

src/compiler/diagnosticMessages.json

@@ -1823,6 +1823,10 @@
         "category": "Error",
         "code": 2609
     },
+    "Cannot augment module '{0}' with value exports because it resolves to a non-module entity.": {
+        "category": "Error",
+        "code": 2649
+    },
     "Cannot emit namespaced JSX elements in React": {
         "category": "Error",
         "code": 2650

tests/baselines/reference/augmentExportEquals7.errors.txt

@@ -0,0 +1,16 @@
+/node_modules/@types/lib-extender/index.d.ts(2,16): error TS2649: Cannot augment module 'lib' with value exports because it resolves to a non-module entity.
+
+
+==== /node_modules/lib/index.d.ts (0 errors) ====
+    declare var lib: () => void;
+    declare namespace lib {}
+    export = lib;
+
+==== /node_modules/@types/lib-extender/index.d.ts (1 errors) ====
+    import * as lib from "lib";
+    declare module "lib" {
+                   ~~~~~
+!!! error TS2649: Cannot augment module 'lib' with value exports because it resolves to a non-module entity.
+        export function fn(): void;
+    }
+

tests/baselines/reference/globalAugmentationModuleResolution.types

@@ -3,7 +3,7 @@
 export { };
 
 declare global {
->global : any
+>global : typeof global
 
   var x: number;
 >x : number

tests/cases/compiler/augmentExportEquals7.ts

@@ -0,0 +1,10 @@
+// @Filename: /node_modules/lib/index.d.ts
+declare var lib: () => void;
+declare namespace lib {}
+export = lib;
+
+// @Filename: /node_modules/@types/lib-extender/index.d.ts
+import * as lib from "lib";
+declare module "lib" {
+    export function fn(): void;
+}