Ensure enum members syntactically determinable to be strings do not get reverse mappings (#57686)

Co-authored-by: frigus02 <3579251+frigus02@users.noreply.github.com>
Co-authored-by: Jan Kühle <jkuehle90@gmail.com>

src/compiler/transformers/ts.ts

@@ -122,6 +122,7 @@ import {
     isSimpleInlineableExpression,
     isSourceFile,
     isStatement,
+    isSyntacticallyString,
     isTemplateLiteral,
     isTryStatement,
     JsxOpeningElement,
@@ -1922,7 +1923,7 @@ export function transformTypeScript(context: TransformationContext) {
             ),
             valueExpression,
         );
-        const outerAssignment = valueExpression.kind === SyntaxKind.StringLiteral ?
+        const outerAssignment = isSyntacticallyString(valueExpression) ?
             innerAssignment :
             factory.createAssignment(
                 factory.createElementAccessExpression(

src/compiler/utilities.ts

@@ -10638,3 +10638,22 @@ export function replaceFirstStar(s: string, replacement: string): string {
 export function getNameFromImportAttribute(node: ImportAttribute) {
     return isIdentifier(node.name) ? node.name.escapedText : escapeLeadingUnderscores(node.name.text);
 }
+
+/** @internal */
+export function isSyntacticallyString(expr: Expression): boolean {
+    expr = skipOuterExpressions(expr);
+    switch (expr.kind) {
+        case SyntaxKind.BinaryExpression:
+            const left = (expr as BinaryExpression).left;
+            const right = (expr as BinaryExpression).right;
+            return (
+                (expr as BinaryExpression).operatorToken.kind === SyntaxKind.PlusToken &&
+                (isSyntacticallyString(left) || isSyntacticallyString(right))
+            );
+        case SyntaxKind.TemplateExpression:
+        case SyntaxKind.StringLiteral:
+        case SyntaxKind.NoSubstitutionTemplateLiteral:
+            return true;
+    }
+    return false;
+}

src/testRunner/unittests/services/transpile.ts

@@ -673,4 +673,13 @@ export * as alias from './file';`,
             options: { compilerOptions: { module: ts.ModuleKind.ESNext, target: ts.ScriptTarget.ESNext } },
         },
     );
+
+    transpilesCorrectly(
+        "Syntactically string but non-evaluatable enum members do not get reverse mapping",
+        // eslint-disable-next-line no-template-curly-in-string
+        "import { BAR } from './bar'; enum Foo { A = `${BAR}` }",
+        {
+            options: { compilerOptions: { target: ts.ScriptTarget.ESNext } },
+        },
+    );
 });