Make struct_tail normalize when possible #62585
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…ing normalization. The old struct tail functions did not deal with `<T as Trait>::A` and `impl Trait`, at least not explicitly. (We didn't notice this bug before because it is only exposed when the tail (post deep normalization) is not `Sized`, so it was a rare case to deal with.) For post type-checking (i.e. during codegen), there is now `struct_tail_erasing_lifetimes` and `struct_lockstep_tails_erasing_lifetimes`, which each take an additional `ParamEnv` argument to drive normalization. For pre type-checking cases where normalization is not needed, there is `struct_tail_without_normalization`. (Currently, the only instance of this is `Expectation::rvalue_hint`.) All of these new entrypoints work by calling out to common helper routines. The helpers are parameterized over a closure that handles the normalization.
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…il-normalize-when-possible, r=eddyb Make struct_tail normalize when possible As noted in commit message: this replaces the existing methods to extract the struct tail(s) with new entry points that make the handling of normalization explicit. Most of the places that call `struct_tail` are during codegen, post type-checking, and therefore they can get away with using `tcx.normalize_erasing_regions` (this is the entry point `struct_tail_erasing_lifetimes`) For other cases that may arise, one can use the core method, which is parameterized over the normalization `Ty -> Ty` closure (`struct_tail_with_normalize`). Or one can use the trivial entry point that does not normalization (`struct_tail_without_normalization`) ---- I spent a little while trying to make a test that exposed the bug via `impl Trait` rather than a projection, but I failed to find something that tripped up the current nightly `rustc`. * I have *not* spent any time trying to make tests that trip up the other places where `struct_tail` was previously being called. While I do think the task of making such tests could be worthwhile, I am simply running out of time. (Its also possible that the layout code is always the first point called, and thus it may be pointless to try to come up with such tests.) I also spent a little time discussing with @eddyb where this code should live. They suggested moving `struct_tail` and its sibling `struct_lockstep_tails` to the `LayoutCx`. But in the interest of time, I have left that refactoring (which may be questionable at this point) to a follow-up task. ---- Fix rust-lang#60431
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Rollup of 5 pull requests Successful merges: - #62577 (Add an AtomicCell abstraction) - #62585 (Make struct_tail normalize when possible) - #62604 (Handle errors during error recovery gracefully) - #62636 (rustbuild: Improve assert about building tools once) - #62651 (Make some rustc macros more hygienic) Failed merges: r? @ghost
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As noted in commit message: this replaces the existing methods to extract the struct tail(s) with new entry points that make the handling of normalization explicit.
Most of the places that call
struct_tailare during codegen, post type-checking, and therefore they can get away with usingtcx.normalize_erasing_regions(this is the entry pointstruct_tail_erasing_lifetimes)For other cases that may arise, one can use the core method, which is parameterized over the normalization
Ty -> Tyclosure (struct_tail_with_normalize).Or one can use the trivial entry point that does not normalization (
struct_tail_without_normalization)I spent a little while trying to make a test that exposed the bug via
impl Traitrather than a projection, but I failed to find something that tripped up the current nightlyrustc.struct_tailwas previously being called. While I do think the task of making such tests could be worthwhile, I am simply running out of time. (Its also possible that the layout code is always the first point called, and thus it may be pointless to try to come up with such tests.)I also spent a little time discussing with @eddyb where this code should live. They suggested moving
struct_tailand its siblingstruct_lockstep_tailsto theLayoutCx. But in the interest of time, I have left that refactoring (which may be questionable at this point) to a follow-up task.Fix #60431