impr: Better error on JS array runtime access

packages/typegpu/src/tgsl/accessIndex.ts

@@ -1,5 +1,5 @@
 import { stitch } from '../core/resolve/stitch.ts';
-import { isDisarray, MatrixColumnsAccess, UnknownData } from '../data/dataTypes.ts';
+import { isDisarray, MatrixColumnsAccess } from '../data/dataTypes.ts';
 import { derefSnippet } from '../data/ref.ts';
 import { isEphemeralSnippet, type Origin, snip, type Snippet } from '../data/snippet.ts';
 import { vec2f, vec3f, vec4f } from '../data/vector.ts';
@@ -101,7 +101,7 @@ export function accessIndex(target: Snippet, indexArg: Snippet | number): Snippe
     );
   }
 
-  if ((isKnownAtComptime(target) && isKnownAtComptime(index)) || target.dataType === UnknownData) {
+  if (isKnownAtComptime(target) && isKnownAtComptime(index)) {
     // No idea what the type is, so we act on the snippet's value and try to guess
     return coerceToSnippet(
       // oxlint-disable-next-line typescript/no-explicit-any -- we're inspecting the value, and it could be any value

packages/typegpu/src/tgsl/wgslGenerator.ts

@@ -556,7 +556,7 @@ ${this.ctx.pre}}`;
         const propertyStr = this.ctx.resolve(property.value, property.dataType).value;
 
         throw new Error(
-          `Unable to index value ${targetStr} of unknown type with index ${propertyStr}. If the value is an array, to address this, consider one of the following approaches: (1) declare the array using 'tgpu.const', (2) store the array in a buffer, or (3) define the array within the GPU function scope.`,
+          `Index access '${targetStr}[${propertyStr}]' is invalid. If the value is an array, to address this, consider one of the following approaches: (1) declare the array using 'tgpu.const', (2) store the array in a buffer, or (3) define the array within the GPU function scope.`,
         );
       }
 

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

@@ -1757,7 +1757,22 @@ describe('wgslGenerator', () => {
     expect(() => tgpu.resolve([testFn])).toThrowErrorMatchingInlineSnapshot(`
       [Error: Resolution of the following tree failed:
       - <root>
-      - fn:testFn: Value undefined (as json: undefined) is not resolvable to type u32]
+      - fn:testFn: Index access 'array(9, 8, 7, 6)[i]' is invalid. If the value is an array, to address this, consider one of the following approaches: (1) declare the array using 'tgpu.const', (2) store the array in a buffer, or (3) define the array within the GPU function scope.]
+    `);
+  });
+
+  it('throws an error when accessing an object with a runtime known index', () => {
+    const Boid = d.struct({ 0: d.u32 });
+
+    const testFn = tgpu.fn([Boid])((b) => {
+      const i = 0;
+      const v = b[i];
+    });
+
+    expect(() => tgpu.resolve([testFn])).toThrowErrorMatchingInlineSnapshot(`
+      [Error: Resolution of the following tree failed:
+      - <root>
+      - fn:testFn: Index access 'b[i]' is invalid. If the value is an array, to address this, consider one of the following approaches: (1) declare the array using 'tgpu.const', (2) store the array in a buffer, or (3) define the array within the GPU function scope.]
     `);
   });