Fix bug: Ensure export = symbol always has a valueDeclaration (#26973)

Author: Andy

src/compiler/binder.ts

@@ -234,13 +234,17 @@ namespace ts {
             }
 
             if (symbolFlags & SymbolFlags.Value) {
-                const { valueDeclaration } = symbol;
-                if (!valueDeclaration ||
-                    (isAssignmentDeclaration(valueDeclaration) && !isAssignmentDeclaration(node)) ||
-                    (valueDeclaration.kind !== node.kind && isEffectiveModuleDeclaration(valueDeclaration))) {
-                    // other kinds of value declarations take precedence over modules and assignment declarations
-                    symbol.valueDeclaration = node;
-                }
+                setValueDeclaration(symbol, node);
+            }
+        }
+
+        function setValueDeclaration(symbol: Symbol, node: Declaration): void {
+            const { valueDeclaration } = symbol;
+            if (!valueDeclaration ||
+                (isAssignmentDeclaration(valueDeclaration) && !isAssignmentDeclaration(node)) ||
+                (valueDeclaration.kind !== node.kind && isEffectiveModuleDeclaration(valueDeclaration))) {
+                // other kinds of value declarations take precedence over modules and assignment declarations
+                symbol.valueDeclaration = node;
             }
         }
 
@@ -2286,14 +2290,19 @@ namespace ts {
                 bindAnonymousDeclaration(node, SymbolFlags.Alias, getDeclarationName(node)!);
             }
             else {
-                const flags = node.kind === SyntaxKind.ExportAssignment && exportAssignmentIsAlias(node)
+                const flags = exportAssignmentIsAlias(node)
                     // An export default clause with an EntityNameExpression or a class expression exports all meanings of that identifier or expression;
                     ? SymbolFlags.Alias
                     // An export default clause with any other expression exports a value
                     : SymbolFlags.Property;
                 // If there is an `export default x;` alias declaration, can't `export default` anything else.
                 // (In contrast, you can still have `export default function f() {}` and `export default interface I {}`.)
-                declareSymbol(container.symbol.exports, container.symbol, node, flags, SymbolFlags.All);
+                const symbol = declareSymbol(container.symbol.exports, container.symbol, node, flags, SymbolFlags.All);
+
+                if (node.isExportEquals) {
+                    // Will be an error later, since the module already has other exports. Just make sure this has a valueDeclaration set.
+                    setValueDeclaration(symbol, node);
+                }
             }
         }
 

tests/baselines/reference/errorForConflictingExportEqualsValue.errors.txt

@@ -1,9 +1,10 @@
-tests/cases/compiler/errorForConflictingExportEqualsValue.ts(2,1): error TS2309: An export assignment cannot be used in a module with other exported elements.
+/a.ts(2,1): error TS2309: An export assignment cannot be used in a module with other exported elements.
 
 
-==== tests/cases/compiler/errorForConflictingExportEqualsValue.ts (1 errors) ====
+==== /a.ts (1 errors) ====
     export var x;
-    export = {};
-    ~~~~~~~~~~~~
+    export = x;
+    ~~~~~~~~~~~
 !!! error TS2309: An export assignment cannot be used in a module with other exported elements.
+    import("./a");
 

tests/baselines/reference/errorForConflictingExportEqualsValue.js

@@ -1,8 +1,10 @@
-//// [errorForConflictingExportEqualsValue.ts]
+//// [a.ts]
 export var x;
-export = {};
+export = x;
+import("./a");
 
 
-//// [errorForConflictingExportEqualsValue.js]
+//// [a.js]
 "use strict";
-module.exports = {};
+Promise.resolve().then(function () { return require("./a"); });
+module.exports = exports.x;

tests/baselines/reference/errorForConflictingExportEqualsValue.symbols

@@ -1,6 +1,10 @@
-=== tests/cases/compiler/errorForConflictingExportEqualsValue.ts ===
+=== /a.ts ===
 export var x;
->x : Symbol(x, Decl(errorForConflictingExportEqualsValue.ts, 0, 10))
+>x : Symbol(x, Decl(a.ts, 0, 10))
 
-export = {};
+export = x;
+>x : Symbol(x, Decl(a.ts, 0, 10))
+
+import("./a");
+>"./a" : Symbol("/a", Decl(a.ts, 0, 0))
 

tests/baselines/reference/errorForConflictingExportEqualsValue.types

@@ -1,7 +1,11 @@
-=== tests/cases/compiler/errorForConflictingExportEqualsValue.ts ===
+=== /a.ts ===
 export var x;
 >x : any
 
-export = {};
->{} : {}
+export = x;
+>x : any
+
+import("./a");
+>import("./a") : Promise<typeof import("/a").x>
+>"./a" : "./a"
 

tests/cases/compiler/errorForConflictingExportEqualsValue.ts

@@ -1,2 +1,5 @@
+// @lib: es6
+// @Filename: /a.ts
 export var x;
-export = {};
+export = x;
+import("./a");