feat(@typegpu/gl): Implicit pointer definitions in GLSL generator - #2819

Pull request overview

This PR adds GLSL-compatible handling for TypeGPU’s “implicit pointer” const-aliasing semantics, enabling the WebGL/GLSL fallback to preserve expected mutation behavior without native pointer support.

Changes:

• Refactors WGSL const-alias handling into an overridable _aliasConstStatement hook.
• Implements GLSL-specific aliasing rules: copy from immutable origins (e.g. uniforms), otherwise inline the aliased l-value expression and hoist runtime index expressions into temporaries to ensure single evaluation.
• Adds a dedicated implicitPointer.test.ts suite covering immutable copies, mutable aliases, runtime index hoisting, and nested/alias-of-alias cases.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

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Reviewed changes

• GLSL alias const statements — _aliasConstStatement override in glslGenerator.ts: copies aliases of immutable memory (uniform/readonly/handle) into locals, and turns mutable-memory aliases into compile-time substitutions of the aliased expression, hoisting non-constant index expressions into once-evaluated temp variables.
• Index hoisting helper — new #hoistIndexAccesses walks member/index accesses and replaces runtime index expressions with @index_N references tied to freshly declared temps; comptime-constant indices are bound directly.
• WGSL generator refactor — the implicit-pointer const handling in wgslGenerator.ts was extracted into a protected _aliasConstStatement hook with line-identical logic (makeUniqueIdentifier(rawId, 'block') preserved); WGSL generator/constant/struct tests still pass (139 tests).
• New test suite — implicitPointer.test.ts with six snapshot tests (immutable copy, mutable substitution, runtime-index hoisting, nested member/index chains, alias-of-an-alias, local-variable alias).

I verified the edge semantics directly: index expressions are snapshotted at the declaration (later reassignment of the index variable doesn't affect the alias, matching WGSL pointer-address semantics), and alias-of-alias chains resolve correctly through the stored expressions.

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cool

Sure!

ℹ️ No critical issues — one stale doc example to fix.

The rework since the last review is clean: dropping the @index_N placeholder scheme in favor of real idx-prefixed temps (unique via makeUniqueIdentifier('idx', 'block')), inlining comptime-constant indices guarded by !possibleSideEffects, and removing undecorateDataType from both branches. I verified the undecorateDataType removal is safe — @location-decorated fields still emit plain GLSL (vec3 p = u.pos;), consistent with the WGSL base _aliasConstStatement which also uses eq.dataType directly. The new multi-index test pins the single-evaluation semantics well.

Reviewed changes

• Reworked #hoistIndexAccesses to substitute comptime-constant indices inline (now guarded by !index.possibleSideEffects) and to hoist runtime indices into once-evaluated idx temps, removing the @index_N placeholder scheme and the #hoistedIndexCount counter entirely.
• Dropped undecorateDataType(...) from both the immutable-copy and mutable-alias branches of _aliasConstStatement so the alias type flows through undecorated, matching the WGSL base treatment.
• Renamed hoisted temps item → idx across the generator and the snapshot suite, and added a hoists multiple index accessed test covering nested 2D indices (boids.$[index]![idx2]!) plus a user variable named idx2.

ℹ️ Nitpicks

• Test description 'hoists multiple index accessed' — should read 'hoists multiple index accesses'.
• The @example on #hoistIndexAccesses still shows the old item/item_1 naming, which no longer matches emitted code.

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