[RaphaelFakhri]

tgpu-gen sorts structs topologically so that each struct is generated after the structs it uses. topologicalSort only looks at the member type and, for arrays, the element type. When a struct is used inside an array of arrays, such as array<array<Cell, 4>, 4>, and is declared later in the WGSL, it is not recorded as a dependency, and generation fails with Unknown data type: Cell.

Changes

• topologicalSort unwraps nested arrays down to their innermost element type before checking for a struct dependency. This also covers the single-level array case that the old code handled separately.
• Adds a structs generator test for a struct used in a nested array and declared after its parent.

Testing

The packages/tgpu-gen tests pass: 33 tests. Without the gen.mjs change, the new test fails with Error: Unknown data type: Cell.

Fixes #3316

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[pullfrog]

✅ No new issues found.

Reviewed changes

• Nested-array dependency unwrapping — topologicalSort now walks every ArrayInfo.format layer down to the innermost element type before checking allStructNames, so a struct used in array<array<Cell, 4>, 4> (or a runtime-sized array<array<Cell, 2>>) is recorded as a dependency of its holder and emitted first.
• Regression test — structs.test.ts adds a Grid/Cell case that asserts Cell is generated before Grid and that the member renders as d.arrayOf(d.arrayOf(Cell, 4), 4).

The change is a strict superset of the previous dependency detection: it adds only real array-element edges, so ordering changes only for inputs that previously threw Unknown data type. I ran the tgpu-gen suite (33 tests pass) and also generated runtime-sized nested arrays, three-level nesting, and an aliased nested-array member locally — all order correctly.

( ◦°^°◦) 🏴‍☠️ Arr, I read the whole diff, ran the tgpu-gen tests, and found no leaks in this here nested-array fix.

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