don't duplicate function properties when emiting definitions of overload signatures (#44235)

src/compiler/transformers/declarations.ts

@@ -574,6 +574,16 @@ namespace ts {
             return false;
         }
 
+        // If the ExpandoFunctionDeclaration have multiple overloads, then we only need to emit properties for the last one.
+        function shouldEmitFunctionProperties(input: FunctionDeclaration) {
+            if (input.body) {
+                return true;
+            }
+
+            const overloadSignatures = input.symbol.declarations?.filter(decl => isFunctionDeclaration(decl) && !decl.body);
+            return !overloadSignatures || overloadSignatures.indexOf(input) === overloadSignatures.length - 1;
+        }
+
         function getBindingNameVisible(elem: BindingElement | VariableDeclaration | OmittedExpression): boolean {
             if (isOmittedExpression(elem)) {
                 return false;
@@ -1194,7 +1204,7 @@ namespace ts {
                         ensureType(input, input.type),
                         /*body*/ undefined
                     ));
-                    if (clean && resolver.isExpandoFunctionDeclaration(input)) {
+                    if (clean && resolver.isExpandoFunctionDeclaration(input) && shouldEmitFunctionProperties(input)) {
                         const props = resolver.getPropertiesOfContainerFunction(input);
                         // Use parseNodeFactory so it is usable as an enclosing declaration
                         const fakespace = parseNodeFactory.createModuleDeclaration(/*decorators*/ undefined, /*modifiers*/ undefined, clean.name || factory.createIdentifier("_default"), factory.createModuleBlock([]), NodeFlags.Namespace);

tests/baselines/reference/declarationEmitFunctionDuplicateNamespace.js

@@ -0,0 +1,23 @@
+//// [declarationEmitFunctionDuplicateNamespace.ts]
+function f(a: 0): 0;
+function f(a: 1): 1;
+function f(a: 0 | 1) {
+    return a;
+}
+
+f.x = 2;
+
+
+//// [declarationEmitFunctionDuplicateNamespace.js]
+function f(a) {
+    return a;
+}
+f.x = 2;
+
+
+//// [declarationEmitFunctionDuplicateNamespace.d.ts]
+declare function f(a: 0): 0;
+declare function f(a: 1): 1;
+declare namespace f {
+    var x: number;
+}

tests/baselines/reference/declarationEmitFunctionDuplicateNamespace.symbols

@@ -0,0 +1,22 @@
+=== tests/cases/compiler/declarationEmitFunctionDuplicateNamespace.ts ===
+function f(a: 0): 0;
+>f : Symbol(f, Decl(declarationEmitFunctionDuplicateNamespace.ts, 0, 0), Decl(declarationEmitFunctionDuplicateNamespace.ts, 0, 20), Decl(declarationEmitFunctionDuplicateNamespace.ts, 1, 20), Decl(declarationEmitFunctionDuplicateNamespace.ts, 4, 1))
+>a : Symbol(a, Decl(declarationEmitFunctionDuplicateNamespace.ts, 0, 11))
+
+function f(a: 1): 1;
+>f : Symbol(f, Decl(declarationEmitFunctionDuplicateNamespace.ts, 0, 0), Decl(declarationEmitFunctionDuplicateNamespace.ts, 0, 20), Decl(declarationEmitFunctionDuplicateNamespace.ts, 1, 20), Decl(declarationEmitFunctionDuplicateNamespace.ts, 4, 1))
+>a : Symbol(a, Decl(declarationEmitFunctionDuplicateNamespace.ts, 1, 11))
+
+function f(a: 0 | 1) {
+>f : Symbol(f, Decl(declarationEmitFunctionDuplicateNamespace.ts, 0, 0), Decl(declarationEmitFunctionDuplicateNamespace.ts, 0, 20), Decl(declarationEmitFunctionDuplicateNamespace.ts, 1, 20), Decl(declarationEmitFunctionDuplicateNamespace.ts, 4, 1))
+>a : Symbol(a, Decl(declarationEmitFunctionDuplicateNamespace.ts, 2, 11))
+
+    return a;
+>a : Symbol(a, Decl(declarationEmitFunctionDuplicateNamespace.ts, 2, 11))
+}
+
+f.x = 2;
+>f.x : Symbol(f.x, Decl(declarationEmitFunctionDuplicateNamespace.ts, 4, 1))
+>f : Symbol(f, Decl(declarationEmitFunctionDuplicateNamespace.ts, 0, 0), Decl(declarationEmitFunctionDuplicateNamespace.ts, 0, 20), Decl(declarationEmitFunctionDuplicateNamespace.ts, 1, 20), Decl(declarationEmitFunctionDuplicateNamespace.ts, 4, 1))
+>x : Symbol(f.x, Decl(declarationEmitFunctionDuplicateNamespace.ts, 4, 1))
+

tests/baselines/reference/declarationEmitFunctionDuplicateNamespace.types

@@ -0,0 +1,24 @@
+=== tests/cases/compiler/declarationEmitFunctionDuplicateNamespace.ts ===
+function f(a: 0): 0;
+>f : typeof f
+>a : 0
+
+function f(a: 1): 1;
+>f : typeof f
+>a : 1
+
+function f(a: 0 | 1) {
+>f : typeof f
+>a : 0 | 1
+
+    return a;
+>a : 0 | 1
+}
+
+f.x = 2;
+>f.x = 2 : 2
+>f.x : number
+>f : typeof f
+>x : number
+>2 : 2
+

tests/cases/compiler/declarationEmitFunctionDuplicateNamespace.ts

@@ -0,0 +1,8 @@
+// @declaration: true
+function f(a: 0): 0;
+function f(a: 1): 1;
+function f(a: 0 | 1) {
+    return a;
+}
+
+f.x = 2;