fix: ArrayExpression - immediate index access#2409
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Pull request overview
Fixes indexing into TGSL array literals by special-casing ArrayExpression targets so immediate index access can resolve correctly.
Changes:
- Added
ArrayExpressionhandling inaccessIndexto return a direct element when the index is comptime-known. - Added tests covering array-literal indexing with comptime-known and runtime-known indices.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| packages/typegpu/src/tgsl/accessIndex.ts | Adds an ArrayExpression fast-path for constant indices to return the selected element snippet directly. |
| packages/typegpu/tests/array.test.ts | Adds snapshots validating codegen for [...][0/1] and arr[i] patterns. |
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| it('array expressions can be indexed into with a comptime-known index', () => { | ||
| function foo() { | ||
| 'use gpu'; | ||
| const i = 2; | ||
| const a = [i, 2][0]; | ||
| const b = [i, 2][1]; | ||
| } |
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The new tests cover constant-vs-variable indices, but they don’t exercise an important edge case for this change: immediate indexing into an array expression that would otherwise be invalid to construct (e.g., containing a non-ephemeral ref/argument ref). Adding a regression test like const v = d.vec2f(...); const x = [d.vec2f(...), v][0]; (and/or selecting the ref element) would better protect this behavior from regressions.
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cieplypolar
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Apr 24, 2026
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reczkok
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aleksanderkatan
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Contributor
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It wasn't immediately obvious to me what would happen in these two cases, so here are two free tests
it('resolves array expression elements when accessed with comptime-known index', () => {
let n = 0;
const next = tgpu.comptime(() => n++);
function foo() {
'use gpu';
const a = [next(), next()][0];
const b = [next(), next()][1];
}
expect(tgpu.resolve([foo])).toMatchInlineSnapshot(`
"fn foo() {
const a = 0;
const b = 3;
}"
`);
});
it('prunes definitions in array expressions accessed with comptime-known index', ({ root }) => {
const u1 = root.createUniform(d.u32, 1);
const u2 = root.createUniform(d.u32, 2);
const u3 = root.createUniform(d.u32, 3);
const u4 = root.createUniform(d.u32, 4);
function foo() {
'use gpu';
const a = [u1.$, u2.$][0];
const b = [u3.$, u4.$][1];
}
expect(tgpu.resolve([foo])).toMatchInlineSnapshot(`
"@group(0) @binding(0) var<uniform> u1: u32;
@group(0) @binding(1) var<uniform> u4: u32;
fn foo() {
let a = u1;
let b = u4;
}"
`);
});
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