Fix nil pointer in transformExpandoAssignment for element access expressions (microsoft#3723)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>

Author: Copilot

internal/transformers/declarations/transform.go

@@ -2259,7 +2259,7 @@ func (tx *DeclarationTransformer) transformExpandoAssignment(node *ast.BinaryExp
 	if isNonContextualKeywordName {
 		namedExports := tx.Factory().NewNamedExports(tx.Factory().NewNodeList(
 			[]*ast.Node{
-				tx.Factory().NewExportSpecifier(false /*isTypeOnly*/, exportName, tx.Factory().NewIdentifier(left.Name().Text())),
+				tx.Factory().NewExportSpecifier(false /*isTypeOnly*/, exportName, tx.Factory().NewIdentifier(property)),
 			},
 		))
 		statements = append(statements, tx.Factory().NewExportDeclaration(nil /*modifiers*/, false /*isTypeOnly*/, namedExports, nil /*moduleSpecifier*/, nil /*attributes*/))

testdata/baselines/reference/compiler/jsExpandoAssignmentElementAccess.js

@@ -0,0 +1,53 @@
+//// [tests/cases/compiler/jsExpandoAssignmentElementAccess.ts] ////
+
+//// [repro.js]
+var x = {};
+x['if'] = 1;
+x['else'] = 1;
+
+
+
+
+//// [repro.d.ts]
+declare var x: {
+    if: number;
+    else: number;
+};
+declare namespace x {
+    var _a: number;
+    export { _a as if };
+}
+declare namespace x {
+    var _b: number;
+    export { _b as else };
+}
+
+
+//// [DtsFileErrors]
+
+
+repro.d.ts(1,13): error TS2300: Duplicate identifier 'x'.
+repro.d.ts(5,19): error TS2300: Duplicate identifier 'x'.
+repro.d.ts(9,19): error TS2300: Duplicate identifier 'x'.
+
+
+==== repro.d.ts (3 errors) ====
+    declare var x: {
+                ~
+!!! error TS2300: Duplicate identifier 'x'.
+        if: number;
+        else: number;
+    };
+    declare namespace x {
+                      ~
+!!! error TS2300: Duplicate identifier 'x'.
+        var _a: number;
+        export { _a as if };
+    }
+    declare namespace x {
+                      ~
+!!! error TS2300: Duplicate identifier 'x'.
+        var _b: number;
+        export { _b as else };
+    }
+    

testdata/baselines/reference/compiler/jsExpandoAssignmentElementAccess.symbols

@@ -0,0 +1,14 @@
+//// [tests/cases/compiler/jsExpandoAssignmentElementAccess.ts] ////
+
+=== repro.js ===
+var x = {};
+>x : Symbol(x, Decl(repro.js, 0, 3))
+
+x['if'] = 1;
+>x : Symbol(x, Decl(repro.js, 0, 3))
+>'if' : Symbol('if', Decl(repro.js, 0, 11))
+
+x['else'] = 1;
+>x : Symbol(x, Decl(repro.js, 0, 3))
+>'else' : Symbol('else', Decl(repro.js, 1, 12))
+

testdata/baselines/reference/compiler/jsExpandoAssignmentElementAccess.types

@@ -0,0 +1,21 @@
+//// [tests/cases/compiler/jsExpandoAssignmentElementAccess.ts] ////
+
+=== repro.js ===
+var x = {};
+>x : { if: number; else: number; }
+>{} : { if: number; else: number; }
+
+x['if'] = 1;
+>x['if'] = 1 : 1
+>x['if'] : number
+>x : { if: number; else: number; }
+>'if' : "if"
+>1 : 1
+
+x['else'] = 1;
+>x['else'] = 1 : 1
+>x['else'] : number
+>x : { if: number; else: number; }
+>'else' : "else"
+>1 : 1
+

testdata/tests/cases/compiler/jsExpandoAssignmentElementAccess.ts

@@ -0,0 +1,9 @@
+// @allowJs: true
+// @checkJs: true
+// @declaration: true
+// @emitDeclarationOnly: true
+
+// @filename: repro.js
+var x = {};
+x['if'] = 1;
+x['else'] = 1;