Inherit function lifetimes for impl-trait

[cjgillot]

Blocked on #103448
Specific diff https://github.com/cjgillot/rust/compare/no-late-fn..variance-rpit

This PR attempts to stop duplicating generic parameters between functions and opaque types.

fn foo<'a, 'b, T>() -> impl Sized + 'a {} // OLD fn foo<'a, 'b, T>() -> foo::<'static, 'static, T>::opaque::<'a> {} opaque foo::<T>::opaque<'a>: Sized + 'a; // OLD post #103448 fn foo<'a, 'b, T>() -> foo::<'static, 'static, T>::opaque::<'a> {} opaque foo::<'_a, '_b, T>::opaque<'a>: Sized + 'a; // NEW fn foo<'a, 'b, T>() -> foo::<'a, 'b, T>::opaque {} opaque foo::<'a, 'b, T>::opaque: Sized + 'a;

This allows to support Self in impl-trait, since we do not replace lifetimes by 'static any more.

The implementation relies on 2 tweaking rules for opaques in 2 places:

• we only relate substs that correspond to captured lifetimes during TypeRelation;
• we only list captured lifetimes in choice region computation.

For simplicity, I encoded the "capturedness" of lifetimes as a variance, Bivariant vs Invariant for unused vs captured lifetimes. The variances_of query used to ICE for opaques.

Writing the PR description made me realize that this strategy can be used without #103448 to support Self in RPIT. I'll probably make such a PR during the week.

r? types

[rustbot]

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in src/librustdoc/clean/types.rs

cc @camelid

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

[compiler-errors]

This allows to support Self in impl-trait, since we do not replace lifetimes by 'static any more.

Can you elaborate on this? I don't have context of what impl Trait currently has issues with.

[bors]

☔ The latest upstream changes (presumably #103337) made this pull request unmergeable. Please resolve the merge conflicts.

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

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configure: rust.debug-assertions := True configure: rust.overflow-checks := True configure: llvm.assertions := True configure: dist.missing-tools := True configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ... configure: writing `config.toml` in current directory configure: configure: run `python /checkout/x.py --help` Attempting with retry: make prepare --- * highest error code: E0790 Found 506 error codes Found 0 error(s) in error codes Done! tidy error: /checkout/compiler/rustc_ast_lowering/src/lib.rs:1467: unexplained "```ignore" doctest; try one: * make the test actually pass, by adding necessary imports and declarations, or * use "```text", if the code is not Rust code, or * use "```compile_fail,Ennnn", if the code is expected to fail at compile time, or * use "```should_panic", if the code is expected to fail at run time, or * use "```no_run", if the code should type-check but not necessary linkable/runnable, or * explain it like "```ignore (cannot-test-this-because-xxxx)", if the annotation cannot be avoided. tidy error: /checkout/compiler/rustc_ast_lowering/src/lib.rs:1474: unexplained "```ignore" doctest; try one: * make the test actually pass, by adding necessary imports and declarations, or * use "```text", if the code is not Rust code, or * use "```compile_fail,Ennnn", if the code is expected to fail at compile time, or * use "```should_panic", if the code is expected to fail at run time, or * use "```no_run", if the code should type-check but not necessary linkable/runnable, or * explain it like "```ignore (cannot-test-this-because-xxxx)", if the annotation cannot be avoided. * 387 features some tidy checks failed Build completed unsuccessfully in 0:00:11 

[bors]

☔ The latest upstream changes (presumably #103623) made this pull request unmergeable. Please resolve the merge conflicts.