Fix/object assign non table source (#1642) (#1710)

RealColdFry · web-flow · commit c3b3a8bb85ed · 2026-04-16T21:58:51.000+02:00
* fix Object.assign crashing when source is a non-table value

`{ ...(cond &amp;&amp; obj) }` short-circuits to `false` when `cond` is falsy. JS
treats this as a no-op (Object.assign coerces primitives to wrapper objects
with no own enumerable properties), but `__TS__ObjectAssign` was iterating
every source unconditionally, so `pairs(false)` errored at runtime.

Skip non-table sources, matching the spec for null/undefined/primitive args.

* refactor __TS__ObjectAssign to emit cleaner Lua

Invert the type guard so it nests the spread loop instead of using `continue`,
which lowered to a `repeat ... until true` + `break` dance. Same behavior,
the bundled helper now reads like the hand-written original.
diff --git a/src/lualib/ObjectAssign.ts b/src/lualib/ObjectAssign.ts
@@ -2,8 +2,10 @@
 export function __TS__ObjectAssign<T extends object>(this: void, target: T, ...sources: T[]): T {
     for (const i of $range(1, sources.length)) {
         const source = sources[i - 1];
-        for (const key in source) {
-            target[key] = source[key];
+        if (type(source) === "table") {
+            for (const key in source) {
+                target[key] = source[key];
+            }
         }
     }
 
diff --git a/test/unit/builtins/object.spec.ts b/test/unit/builtins/object.spec.ts
@@ -10,6 +10,16 @@ test.each([
     util.testExpression`Object.assign(${util.formatCode(initial)}, ${argsString})`.expectToMatchJsResult();
 });
 
+test.each([
+    "Object.assign({}, false)",
+    "Object.assign({}, null)",
+    "Object.assign({}, undefined)",
+    "Object.assign({}, null, undefined)",
+    "Object.assign({ a: 1 }, false, { b: 2 })",
+])("Object.assign skips non-object sources (%p)", expression => {
+    util.testExpression(expression).expectToMatchJsResult();
+});
+
 test.each([{}, { abc: 3 }, { abc: 3, def: "xyz" }])("Object.entries (%p)", obj => {
     const testBuilder = util.testExpressionTemplate`Object.entries(${obj})`;
     // Need custom matcher because order is not guaranteed in neither JS nor Lua
diff --git a/test/unit/spread.spec.ts b/test/unit/spread.spec.ts
@@ -119,6 +119,15 @@ describe("in object literal", () => {
         util.testExpression(expression).expectToMatchJsResult();
     });
 
+    test.each([
+        "{ ...((false && { a: 1 }) as any) }",
+        "{ ...((true && { a: 1 }) as any) }",
+        "{ a: 1, ...((false && { b: 2 }) as any) }",
+        "{ ...(null as any), ...(undefined as any) }",
+    ])("of short-circuited operand (%p)", expression => {
+        util.testExpression(expression).expectToMatchJsResult();
+    });
+
     test("of object reference", () => {
         util.testFunction`
             const object = { x: 0, y: 1 };

Original file line number	Diff line number	Diff line change
`@@ -2,8 +2,10 @@`
`2`	`2`	`export function __TS__ObjectAssign<T extends object>(this: void, target: T, ...sources: T[]): T {`
`3`	`3`	`for (const i of $range(1, sources.length)) {`
`4`	`4`	`const source = sources[i - 1];`
`5`		`- for (const key in source) {`
`6`		`- target[key] = source[key];`
	`5`	`+ if (type(source) === "table") {`
	`6`	`+ for (const key in source) {`
	`7`	`+ target[key] = source[key];`
	`8`	`+ }`
`7`	`9`	`}`
`8`	`10`	`}`
`9`	`11`