Fix crash when trying to assign to an optional chain (#1045)

Perryvw · web-flow · commit 69a44a6dd338 · 2021-08-03T21:25:40.000+02:00
diff --git a/src/transformation/utils/diagnostics.ts b/src/transformation/utils/diagnostics.ts
@@ -143,3 +143,7 @@ export const annotationDeprecated = createWarningDiagnosticFactory(
         `'@${kind}' is deprecated and will be removed in a future update. Please update your code before upgrading to the next release, otherwise your project will no longer compile. ` +
         `See https://typescripttolua.github.io/docs/advanced/compiler-annotations#${kind.toLowerCase()} for more information.`
 );
+
+export const notAllowedOptionalAssignment = createErrorDiagnosticFactory(
+    "The left-hand side of an assignment expression may not be an optional property access."
+);
diff --git a/src/transformation/visitors/binary-expression/assignments.ts b/src/transformation/visitors/binary-expression/assignments.ts
@@ -16,6 +16,7 @@ import {
     ImmediatelyInvokedFunctionParameters,
     transformToImmediatelyInvokedFunctionExpression,
 } from "../../utils/transform";
+import { notAllowedOptionalAssignment } from "../../utils/diagnostics";
 
 export function transformAssignmentLeftHandSideExpression(
     context: TransformationContext,
@@ -36,6 +37,11 @@ export function transformAssignment(
     right: lua.Expression,
     parent?: ts.Expression
 ): lua.Statement[] {
+    if (ts.isOptionalChain(lhs)) {
+        context.diagnostics.push(notAllowedOptionalAssignment(lhs));
+        return [];
+    }
+
     if (isArrayLength(context, lhs)) {
         const arrayLengthAssignment = lua.createExpressionStatement(
             transformLuaLibFunction(
diff --git a/test/unit/optionalChaining.spec.ts b/test/unit/optionalChaining.spec.ts
@@ -1,3 +1,4 @@
+import { notAllowedOptionalAssignment } from "../../src/transformation/utils/diagnostics";
 import * as util from "../util";
 
 test.each(["null", "undefined", '{ foo: "foo" }'])("optional chaining (%p)", value => {
@@ -97,6 +98,15 @@ test("no side effects", () => {
     `.expectToMatchJsResult();
 });
 
+// Test for https://github.com/TypeScriptToLua/TypeScriptToLua/issues/1044
+test("does not crash when incorrectly used in assignment (#1044)", () => {
+    const { diagnostics } = util.testFunction`
+        foo?.bar = "foo";
+    `.getLuaResult();
+
+    expect(diagnostics.find(d => d.code === notAllowedOptionalAssignment.code)).toBeDefined();
+});
+
 describe("optional chaining function calls", () => {
     test.each(["() => 4", "undefined"])("stand-alone optional function (%p)", value => {
         util.testFunction`
