Only prefer param-env candidates if they remain non-global after norm

[compiler-errors]

Introduce CandidateSource::GlobalParamEnv, and dynamically compute the CandidateSource based on whether the predicate contains params post-normalization.

This code needs some cleanup and documentation. I'm just putting this up for review.

cc rust-lang/trait-system-refactor-initiative#179

r? lcnr

[rustbot]

HIR ty lowering was modified

cc @fmease

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[rust-log-analyzer]

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

Click to see the possible cause of the failure (guessed by this bot)

 Documenting rustc_next_trait_solver v0.0.0 (/checkout/compiler/rustc_next_trait_solver)
error: unresolved link to `I::DefId`
   --> compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs:161:15
    |
161 |     /// and [`I::DefId`].
    |               ^^^^^^^^ no item named `I` in scope
    |
    = note: `-D rustdoc::broken-intra-doc-links` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(rustdoc::broken_intra_doc_links)]`

error: could not document `rustc_next_trait_solver`
warning: build failed, waiting for other jobs to finish...
Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:01:31
  local time: Thu Apr 24 16:40:45 UTC 2025
  network time: Thu, 24 Apr 2025 16:40:45 GMT
##[error]Process completed with exit code 1.
Post job cleanup.

[lcnr]

vibe: bool on CandidateSource::ParamEnv seems nicer

[lcnr]

pls add test

trait With {
    type Assoc;
}
impl<T> With for T {
    type Assoc = T;
}

trait Incomplete<T> {}
impl<T> Incomplete<T> for () {}
fn impls_incomplete<T: Incomplete<U>, U>() {}
fn foo<T>()
where
    u32: With<Assoc = T>,
    (): Incomplete<<u32 as With>::Assoc>,
{
    impls_incomplete::<(), _>();
}

fn main() {}

edit: actually, added as part of #140313

[bors]

☔ The latest upstream changes (presumably #140324) made this pull request unmergeable. Please resolve the merge conflicts.