Auto merge of #123468 - compiler-errors:precise-capturing, r=oli-obk

Implement syntax for `impl Trait` to specify its captures explicitly (`feature(precise_capturing)`)

Implements `impl use<'a, 'b, T, U> Sized` syntax that allows users to explicitly list the captured parameters for an opaque, rather than inferring it from the opaque's bounds (or capturing *all* lifetimes under 2024-edition capture rules). This allows us to exclude some implicit captures, so this syntax may be used as a migration strategy for changes due to #117587.

We represent this list of captured params as `PreciseCapturingArg` in AST and HIR, resolving them between `rustc_resolve` and `resolve_bound_vars`. Later on, we validate that the opaques only capture the parameters in this list.

We artificially limit the feature to *require* mentioning all type and const parameters, since we don't currently have support for non-lifetime bivariant generics. This can be relaxed in the future.

We also may need to limit this to require naming *all* lifetime parameters for RPITIT, since GATs have no variance. I have to investigate this. This can also be relaxed in the future.

r? `@oli-obk`

Tracking issue:

- https://github.com/rust-lang/rust/issues/123432

1 files changed, 2 insertions, 0 deletions

diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index 399bbf166e6..c0c773c6285 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -910,6 +910,7 @@ impl<'hir> Map<'hir> {
             Node::Crate(item) => item.spans.inner_span,
             Node::WhereBoundPredicate(pred) => pred.span,
             Node::ArrayLenInfer(inf) => inf.span,
+            Node::PreciseCapturingNonLifetimeArg(param) => param.ident.span,
             Node::Synthetic => unreachable!(),
             Node::Err(span) => *span,
         }
@@ -1183,6 +1184,7 @@ fn hir_id_to_string(map: Map<'_>, id: HirId) -> String {
         Node::ArrayLenInfer(_) => node_str("array len infer"),
         Node::Synthetic => unreachable!(),
         Node::Err(_) => node_str("error"),
+        Node::PreciseCapturingNonLifetimeArg(_param) => node_str("parameter"),
     }
 }