Fix large_futures ICE with the next solver

[tamird]

With the new trait solver enabled by default in nightly-2026-08-22 1, large_futures can ICE while inspecting an awaited future.

The lint switches to Codegen mode to obtain coroutine layouts but passes a type whose opaque aliases are still marked rigid from type checking. Because layout_of receives an already-Codegen environment, its environment-change path does not clear those markers.

Clear alias rigidity and normalize the awaited type in that environment before querying its layout. Codegen mode must remain: post-analysis layout queries cannot compute coroutine sizes 2.

The regression covers direct and pinned futures under both solvers, without other lint errors that could hide a delayed ICE.

Fixes rust-lang/rust#161495.

changelog: [large_futures]: Fix an ICE on awaited futures with the next trait solver.

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[tamird]

r? @jdonszelmann

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[CommanderStorm]

community review:
not entirely sure I follow why ty::set_aliases_to_non_rigid (that would require a bit of deeper context that @jdonszelmann is likely better to judge 😅), but explanation and testcase sounds plausible to me.

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[tamird]

@CommanderStorm

not entirely sure I follow why ty::set_aliases_to_non_rigid

The rigidity marker is specific to the environment where the alias was normalized. We switch to Codegen, so those aliases need to be reconsidered in the new environment. The original design review explicitly requested resetting rigidity alongside the environment change.

layout_of already does this when it changes environments itself, but here it receives an already-Codegen environment, so that reset is skipped. The patch uses the same reset-then-normalize pattern as rustc's MIR mode-transition pass.

[CommanderStorm]

Ah, makes sense.

[jdonszelmann]

This seems correct to me. Only thing I'm afraid of is that more of clippy may be using the wrong typing mode w.r.t. the new trait solver. Lemme do a quick investigation. Otherwise if I were a clippy maintainer

[jdonszelmann]

is_uninit_value_valid_for_ty_fallback should probably also use codegen (it calls into layout_of right after), that's the only other example I could find

[tamird]

@jdonszelmann

is_uninit_value_valid_for_ty_fallback should probably also use codegen

I checked that path: its local PostAnalysis environment is used only to normalize field types. Recursive checks return to cx.layout_of with the original LateContext environment, so layout_of still performs its own mode transition and rigidity reset. Changing the fallback's local environment to Codegen alone wouldn't change those layout queries' mode.

The existing uninit_assumed_init and uninit_vec fixtures also complete under both solvers with matching warnings, kept nonfatal so delayed ICEs remain visible. I haven't found a reason to change that helper in this PR.

CI is green. If you're happy with the current patch, could you submit an approving GitHub review? CommanderStorm has approved; Clippy needs two community approvals before assigning a maintainer.

[jdonszelmann]

approved officially, after my previous comment :)

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r? @dswij

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[flip1995]

r? @flip1995

Testing this commit in #17607 as well. But LGTM. Once lintcheck passes there I'll merge this and sync it to the Rust repo.

[flip1995]

Awesome, thanks for the quick fix 🙏

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