fix: tgpu.unroll removing ranges ending at zero

[vende11s]

before fix:

  it('', () => {
    const fn = () => {
      'use gpu';
      let res = 0;
      for (const i of tgpu.unroll(std.range(3, 0, -1))) {
        res += i;
      }
      return res;
    };

    expect(tgpu.resolve([fn])).toMatchInlineSnapshot(`
      "fn fn_1() -> i32 {
        let res = 0;
        return res;
      }"
    `);
  });

[github-actions]

pkg.pr.new

packages
Ready to be installed by your favorite package manager ⬇️

https://pkg.pr.new/software-mansion/TypeGPU/eslint-plugin-typegpu@d167c7b904a3b3060f8777a3225a7349f45fd310

https://pkg.pr.new/software-mansion/TypeGPU/tinyest@d167c7b904a3b3060f8777a3225a7349f45fd310

https://pkg.pr.new/software-mansion/TypeGPU/tinyest-for-wgsl@d167c7b904a3b3060f8777a3225a7349f45fd310

https://pkg.pr.new/software-mansion/TypeGPU/typegpu@d167c7b904a3b3060f8777a3225a7349f45fd310

https://pkg.pr.new/software-mansion/TypeGPU/@typegpu/gl@d167c7b904a3b3060f8777a3225a7349f45fd310

https://pkg.pr.new/software-mansion/TypeGPU/unplugin-typegpu@d167c7b904a3b3060f8777a3225a7349f45fd310

benchmark
view benchmark

commit
view commit

[Copilot]

🟡 Changes recommended

Add regression coverage for descending ranges ending at zero.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Fixes tgpu.unroll for descending ranges ending at zero.

Changes:

• Removes the premature zero-endpoint return.
• Checks materialized elements before omitting empty loops.

File summaries

File	Summary	Review comment
packages/typegpu/src/tgsl/wgslGenerator.ts	Corrects compile-time range unrolling.	Add a regression test for std.range(3, 0, -1) and ideally negative endpoints.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[github-actions]

Resolution Time Benchmark

---
config:
  themeVariables:
    xyChart:
      plotColorPalette: "#E63946, #3B82F6, #059669"
---
xychart
  title "Random Branching (🔴 PR | 🔵 main | 🟢 release)"
  x-axis "max depth" [1, 2, 3, 4, 5, 6, 7, 8]
  y-axis "time (ms)"
  line [0.91, 1.74, 3.79, 6.38, 7.56, 10.91, 22.23, 25.07]
  line [0.94, 1.84, 4.01, 6.21, 6.69, 12.73, 23.83, 22.62]
  line [0.88, 1.83, 3.80, 6.36, 7.08, 11.83, 23.18, 24.30]

Loading

---
config:
  themeVariables:
    xyChart:
      plotColorPalette: "#E63946, #3B82F6, #059669"
---
xychart
  title "Linear Recursion (🔴 PR | 🔵 main | 🟢 release)"
  x-axis "max depth" [1, 2, 3, 4, 5, 6, 7, 8]
  y-axis "time (ms)"
  line [0.30, 0.49, 0.66, 0.73, 1.03, 1.06, 1.29, 1.43]
  line [0.34, 0.44, 0.68, 0.76, 1.03, 1.15, 1.46, 1.46]
  line [0.33, 0.50, 0.60, 0.74, 1.10, 1.06, 1.28, 1.50]

Loading

---
config:
  themeVariables:
    xyChart:
      plotColorPalette: "#E63946, #3B82F6, #059669"
---
xychart
  title "Full Tree (🔴 PR | 🔵 main | 🟢 release)"
  x-axis "max depth" [1, 2, 3, 4, 5, 6, 7, 8]
  y-axis "time (ms)"
  line [0.91, 1.98, 3.67, 6.46, 11.33, 24.08, 53.82, 110.30]
  line [0.98, 1.95, 3.75, 7.02, 11.49, 25.13, 54.70, 107.80]
  line [0.92, 1.96, 3.50, 6.29, 11.63, 26.19, 54.30, 108.45]

Loading

[github-actions]

Bundle size comparison (import * as ... in PR vs import * as ... in target):

🟢 Decreased	➖ Unchanged	🔴 Increased	❔ Unknown
0	325	0	0

No notable changes.

If you wish to run a comparison for other, slower bundlers, run the 'Tree-shake test' from the GitHub Actions menu.

[pullfrog]

ℹ️ No critical issues — one minor suggestion. The fix itself is correct and verified.

Reviewed changes

• Correct empty-range detection in tgpu.unroll — packages/typegpu/src/tgsl/wgslGenerator.ts now builds elements first and returns empty code only when elements.length === 0, instead of bailing when range.end.value === 0. This removes the end-value/element-count conflation that dropped descending ranges ending at zero, and it also avoids the previous undefined elements[0] path for empty ranges whose end is non-zero (e.g. std.range(0, 5, -1)).
• I verified the PR's case resolves to 3 iterations (3i, 2i, 1i), that std.range(3, -1, -1) resolves to 4, and that std.range(0, 5, -1) / std.range(0) still emit an empty body. The existing 28 tests in packages/typegpu/tests/unroll.test.ts all pass.

ℹ️ Missing regression test

This is a bug fix but ships without a committed test — changed_files: 1, and the failing snippet in the PR description was not added. unroll.test.ts has no descending-range (negative step) case, so nothing pins this behavior and a future refactor could silently reintroduce it.

Technical details

# Add a regression test for descending ranges / zero-end ranges

## Affected sites
- `packages/typegpu/tests/unroll.test.ts` — no `std.range` case with a negative step; existing range tests use `std.range(1, 9, 2)` (L813) and `std.range(1, 10)` (L906).

## Required outcome
- A test that fails against the pre-fix `wgslGenerator.ts` and passes now. The PR description's `std.range(3, 0, -1)` case is ideal (expects unrolled iterations `#0`→`3i`, `#1`→`2i`, `#2`→`1i`).
- Optionally also pin the empty-but-nonzero-end case (`std.range(0, 5, -1)`), which previously crashed on `elements[0]`.

## Suggested approach
- Add an `it(...)` to `packages/typegpu/tests/unroll.test.ts` using the existing `tgpu.resolve([fn])` + `toMatchInlineSnapshot` idiom, alongside the `'unrolls a range'` test (L809).

  ^{｜ Fix it ➔ ｜ View workflow run ｜ Using DeepSeek Flash (free via Pullfrog for OSS) ｜ 𝕏}

[pullfrog]

✅ No new issues found.

Reviewed changes

• Added regression test for descending ranges ending at zero — packages/typegpu/tests/tgsl/wgslGenerator.test.ts now pins tgpu.unroll(std.range(3, 0, -1)) to three unrolled iterations (3i, 2i, 1i) plus a CPU main() === 6 assertion.
• Added regression test for empty ranges with a nonzero endpoint — pins std.range(3, 3) to an empty body and CPU main() === 0, covering the previous elements[0] undefined crash.
• Both tests were verified to fail against the pre-fix generator (snapshot mismatch for the descending case; TypeError in isAlias for the empty case) and to pass with the fix. The full wgslGenerator.test.ts (104 tests) and unroll.test.ts (28 tests) suites pass.

  ^{｜ View workflow run ｜ Using DeepSeek Flash (free via Pullfrog for OSS) ｜ 𝕏}

[cieplypolar]

Nice catch 🚢 🇮🇹

[aleksanderkatan]

lesgooo

[reczkok]

yup