1 files changed, 39 insertions, 4 deletions
diff --git a/compiler/rustc_borrowck/src/diagnostics/mod.rs b/compiler/rustc_borrowck/src/diagnostics/mod.rs
index 5e3f3ffa2ea..7b4e38969ee 100644
--- a/compiler/rustc_borrowck/src/diagnostics/mod.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/mod.rs
@@ -7,17 +7,17 @@ use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::{Applicability, Diag, EmissionGuarantee, MultiSpan, listify};
 use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::{self as hir, CoroutineKind, LangItem};
-use rustc_index::IndexSlice;
+use rustc_index::{IndexSlice, IndexVec};
 use rustc_infer::infer::{BoundRegionConversionTime, NllRegionVariableOrigin};
 use rustc_infer::traits::SelectionError;
-use rustc_middle::bug;
 use rustc_middle::mir::{
     AggregateKind, CallSource, ConstOperand, ConstraintCategory, FakeReadCause, Local, LocalInfo,
     LocalKind, Location, Operand, Place, PlaceRef, PlaceTy, ProjectionElem, Rvalue, Statement,
-    StatementKind, Terminator, TerminatorKind, find_self_call,
+    StatementKind, Terminator, TerminatorKind, VarDebugInfoContents, find_self_call,
 };
 use rustc_middle::ty::print::Print;
 use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::{bug, span_bug};
 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult, MoveOutIndex};
 use rustc_span::def_id::LocalDefId;
 use rustc_span::source_map::Spanned;
@@ -190,6 +190,36 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     ) -> Option<&(PlaceRef<'tcx>, Diag<'infcx>)> {
         self.diags_buffer.buffered_move_errors.get(move_out_indices)
     }
+
+    /// Uses `body.var_debug_info` to find the symbol
+    fn local_name(&self, index: Local) -> Option<Symbol> {
+        *self.local_names().get(index)?
+    }
+
+    fn local_names(&self) -> &IndexSlice<Local, Option<Symbol>> {
+        self.local_names.get_or_init(|| {
+            let mut local_names = IndexVec::from_elem(None, &self.body.local_decls);
+            for var_debug_info in &self.body.var_debug_info {
+                if let VarDebugInfoContents::Place(place) = var_debug_info.value {
+                    if let Some(local) = place.as_local() {
+                        if let Some(prev_name) = local_names[local]
+                            && var_debug_info.name != prev_name
+                        {
+                            span_bug!(
+                                var_debug_info.source_info.span,
+                                "local {:?} has many names (`{}` vs `{}`)",
+                                local,
+                                prev_name,
+                                var_debug_info.name
+                            );
+                        }
+                        local_names[local] = Some(var_debug_info.name);
+                    }
+                }
+            }
+            local_names
+        })
+    }
 }
 
 impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
@@ -430,7 +460,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     /// a name, or its name was generated by the compiler, then `Err` is returned
     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
         let decl = &self.body.local_decls[local];
-        match self.local_names[local] {
+        match self.local_name(local) {
             Some(name) if !decl.from_compiler_desugaring() => {
                 buf.push_str(name.as_str());
                 Ok(())
@@ -1500,4 +1530,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             }
         }
     }
+
+    /// Skip over locals that begin with an underscore or have no name
+    pub(crate) fn local_excluded_from_unused_mut_lint(&self, index: Local) -> bool {
+        self.local_name(index).is_none_or(|name| name.as_str().starts_with('_'))
+    }
 }