TypeScriptToLua · Perryvw · Feb 26, 2023 · Feb 26, 2023 · Feb 26, 2023
diff --git a/src/transformation/utils/diagnostics.ts b/src/transformation/utils/diagnostics.ts
@@ -1,4 +1,5 @@
 import * as ts from "typescript";
+import * as lua from "../../LuaAST";
 import { LuaTarget, TypeScriptToLuaOptions } from "../../CompilerOptions";
 import { createSerialDiagnosticFactory } from "../../utils";
 import { AnnotationKind } from "./annotations";
@@ -163,3 +164,7 @@ export const invalidMethodCallExtensionUse = createErrorDiagnosticFactory(
 export const invalidSpreadInCallExtension = createErrorDiagnosticFactory(
     "Spread elements are not supported in call extensions."
 );
+
+export const cannotAssignToNodeOfKind = createErrorDiagnosticFactory(
+    (kind: lua.SyntaxKind) => `Cannot create assignment assigning to a node of type ${lua.SyntaxKind[kind]}.`
+);
diff --git a/src/transformation/visitors/binary-expression/assignments.ts b/src/transformation/visitors/binary-expression/assignments.ts
@@ -1,6 +1,5 @@
 import * as ts from "typescript";
 import * as lua from "../../../LuaAST";
-import { cast } from "../../../utils";
 import { TransformationContext } from "../../context";
 import { validateAssignment } from "../../utils/assignment-validation";
 import { createExportedIdentifier, getDependenciesOfSymbol, isSymbolExported } from "../../utils/export";
@@ -9,7 +8,7 @@ import { LuaLibFeature, transformLuaLibFunction } from "../../utils/lualib";
 import { isArrayType, isDestructuringAssignment } from "../../utils/typescript";
 import { isArrayLength, transformDestructuringAssignment } from "./destructuring-assignments";
 import { isMultiReturnCall } from "../language-extensions/multi";
-import { notAllowedOptionalAssignment } from "../../utils/diagnostics";
+import { cannotAssignToNodeOfKind, notAllowedOptionalAssignment } from "../../utils/diagnostics";
 import { transformElementAccessArgument } from "../access";
 import { moveToPrecedingTemp, transformExpressionList } from "../expression-list";
 import { transformInPrecedingStatementScope } from "../../utils/preceding-statements";
@@ -37,9 +36,16 @@ export function transformAssignmentLeftHandSideExpression(
     const symbol = context.checker.getSymbolAtLocation(node);
     const left = context.transformExpression(node);
 
-    return lua.isIdentifier(left) && symbol && isSymbolExported(context, symbol)
-        ? createExportedIdentifier(context, left)
-        : cast(left, lua.isAssignmentLeftHandSideExpression);
+    if (lua.isIdentifier(left) && symbol && isSymbolExported(context, symbol)) {
+        return createExportedIdentifier(context, left);
+    }
+
+    if (lua.isAssignmentLeftHandSideExpression(left)) {
+        return left;
+    } else {
+        context.diagnostics.push(cannotAssignToNodeOfKind(node, left.kind));
+        return lua.createAnonymousIdentifier();
+    }
 }
 
 export function transformAssignment(

diff --git a/test/unit/builtins/string.spec.ts b/test/unit/builtins/string.spec.ts
@@ -401,12 +401,10 @@ test.each(["string | undefined", "string | null", "null | string", "null | undef
 
 // https://github.com/TypeScriptToLua/TypeScriptToLua/issues/1406
 test("string.indexOf without arguments (#1406)", () => {
-    // Just test we do not throw here
-    util.testExpression`"".indexOf()`.expectToHaveDiagnostics();
+    util.testExpression`"".indexOf()`.expectNoTranspileException();
 });
 
 // https://github.com/TypeScriptToLua/TypeScriptToLua/issues/1406
 test("string.repeat without arguments (#1406)", () => {
-    // Just test we do not throw here
-    util.testExpression`"".repeat()`.expectToHaveDiagnostics();
+    util.testExpression`"".repeat()`.expectNoTranspileException();
 });
diff --git a/test/unit/destructuring.spec.ts b/test/unit/destructuring.spec.ts
@@ -1,3 +1,4 @@
+import { cannotAssignToNodeOfKind, invalidMultiReturnAccess } from "../../src/transformation/utils/diagnostics";
 import * as util from "../util";
 
 const allBindings = "x, y, z, rest";
@@ -225,3 +226,14 @@ describe("array destructuring optimization", () => {
             .expectToMatchJsResult();
     });
 });
+
+test("no exception from semantically invalid TS", () => {
+    util.testModule`
+        declare function testFunc(value: number): LuaMultiReturn<[number, number]>;
+        let [a, b] = testFunc(5) // Missing ;
+        [a, b] = testFunc(b)     // Interpreted as testFunc(5)[a, b]
+    `
+        .withLanguageExtensions()
+        .disableSemanticCheck()
+        .expectToHaveDiagnostics([invalidMultiReturnAccess.code, cannotAssignToNodeOfKind.code]);
+});
diff --git a/test/util.ts b/test/util.ts
@@ -346,6 +346,11 @@ export abstract class TestBuilder {
         return this;
     }
 
+    public expectNoTranspileException(): this {
+        expect(() => this.getLuaResult()).not.toThrow();
+        return this;
+    }
+
     public expectNoExecutionError(): this {
         const luaResult = this.getLuaExecutionResult();
         if (luaResult instanceof ExecutionError) {