fix: Allow arguments in rhs of compound assignment (#2219)

Author: iwoplaza

packages/typegpu/src/tgsl/wgslGenerator.ts

@@ -410,7 +410,9 @@ ${this.ctx.pre}}`;
           );
         }
 
+        // Compound assignment operators are okay, e.g. +=, -=, *=, /=, ...
         if (
+          op === '=' &&
           rhsExpr.origin === 'argument' &&
           !wgsl.isNaturallyEphemeral(rhsExpr.dataType)
         ) {

packages/typegpu/tests/tgsl/operatorOverloads.test.ts

@@ -111,6 +111,43 @@ test('vec3f() %', () => {
   );
 });
 
+test('+= refOfVec3f', () => {
+  const constant = tgpu.const(d.vec3f, d.vec3f(-10));
+  const foo = (arg: d.v3f) => {
+    'use gpu';
+    const local = d.vec3f(100, 10, 1);
+
+    let result = d.vec3f();
+    result += local;
+    result += arg;
+    result += constant.$;
+    return result;
+  };
+
+  const main = () => {
+    'use gpu';
+    return foo(d.vec3f(1, 2, 3));
+  };
+
+  expect(tgpu.resolve([main])).toMatchInlineSnapshot(`
+    "const constant: vec3f = vec3f(-10);
+
+    fn foo(arg: vec3f) -> vec3f {
+      var local = vec3f(100, 10, 1);
+      var result = vec3f();
+      result += local;
+      result += arg;
+      result += constant;
+      return result;
+    }
+
+    fn main() -> vec3f {
+      return foo(vec3f(1, 2, 3));
+    }"
+  `);
+  expect(main().toString()).toMatchInlineSnapshot(`"vec3f(91, 2, -6)"`);
+});
+
 describe('num op', () => {
   test('num +', () => {
     const main = () => {