Auto merge of #85020 - lrh2000:named-upvars, r=tmandry

Name the captured upvars for closures/generators in debuginfo

Previously, debuggers print closures as something like
```
y::main::closure-0 (0x7fffffffdd34)
```
The pointer actually references to an upvar. It is not very obvious, especially for beginners.

It's because upvars don't have names before, as they are packed into a tuple. This PR names the upvars, so we can expect to see something like
```
y::main::closure-0 {_captured_ref__b: 0x[...]}
```

r? `@tmandry`
Discussed at https://github.com/rust-lang/rust/pull/84752#issuecomment-831639489 .

1 files changed, 8 insertions, 13 deletions

diff --git a/compiler/rustc_mir_build/src/build/mod.rs b/compiler/rustc_mir_build/src/build/mod.rs
index 0d623806eb7..b8c3e81aa8f 100644
--- a/compiler/rustc_mir_build/src/build/mod.rs
+++ b/compiler/rustc_mir_build/src/build/mod.rs
@@ -15,7 +15,7 @@ use rustc_middle::mir::*;
 use rustc_middle::thir::{BindingMode, Expr, ExprId, LintLevel, PatKind, Thir};
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeckResults};
-use rustc_span::symbol::{kw, sym};
+use rustc_span::symbol::sym;
 use rustc_span::Span;
 use rustc_target::spec::abi::Abi;
 
@@ -902,13 +902,16 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 ty::Generator(_, substs, _) => ty::UpvarSubsts::Generator(substs),
                 _ => span_bug!(self.fn_span, "upvars with non-closure env ty {:?}", closure_ty),
             };
+            let def_id = self.def_id.as_local().unwrap();
+            let capture_syms = tcx.symbols_for_closure_captures((def_id, fn_def_id));
             let capture_tys = upvar_substs.upvar_tys();
-            let captures_with_tys =
-                hir_typeck_results.closure_min_captures_flattened(fn_def_id).zip(capture_tys);
+            let captures_with_tys = hir_typeck_results
+                .closure_min_captures_flattened(fn_def_id)
+                .zip(capture_tys.zip(capture_syms));
 
             self.upvar_mutbls = captures_with_tys
                 .enumerate()
-                .map(|(i, (captured_place, ty))| {
+                .map(|(i, (captured_place, (ty, sym)))| {
                     let capture = captured_place.info.capture_kind;
                     let var_id = match captured_place.place.base {
                         HirPlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
@@ -917,14 +920,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
                     let mutability = captured_place.mutability;
 
-                    // FIXME(project-rfc-2229#8): Store more precise information
-                    let mut name = kw::Empty;
-                    if let Some(Node::Binding(pat)) = tcx_hir.find(var_id) {
-                        if let hir::PatKind::Binding(_, _, ident, _) = pat.kind {
-                            name = ident.name;
-                        }
-                    }
-
                     let mut projs = closure_env_projs.clone();
                     projs.push(ProjectionElem::Field(Field::new(i), ty));
                     match capture {
@@ -935,7 +930,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     };
 
                     self.var_debug_info.push(VarDebugInfo {
-                        name,
+                        name: sym,
                         source_info: SourceInfo::outermost(tcx_hir.span(var_id)),
                         value: VarDebugInfoContents::Place(Place {
                             local: ty::CAPTURE_STRUCT_LOCAL,