From b19d5c05929bc4ead9b127b8e28aa6c7a40119da Mon Sep 17 00:00:00 2001
From: Dylan MacKenzie <ecstaticmorse@gmail.com>
Date: Sat, 16 May 2020 13:41:30 -0700
Subject: [PATCH] Name return place in debuginfo if it is a user variable

---
 src/librustc_codegen_ssa/mir/debuginfo.rs | 3 ++-
 src/librustc_mir/transform/nrvo.rs        | 4 ++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/librustc_codegen_ssa/mir/debuginfo.rs b/src/librustc_codegen_ssa/mir/debuginfo.rs
index 5501ed5128d..d166a27b5a9 100644
--- a/src/librustc_codegen_ssa/mir/debuginfo.rs
+++ b/src/librustc_codegen_ssa/mir/debuginfo.rs
@@ -115,7 +115,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         let full_debug_info = bx.sess().opts.debuginfo == DebugInfo::Full;
 
         // FIXME(eddyb) maybe name the return place as `_0` or `return`?
-        if local == mir::RETURN_PLACE {
+        if local == mir::RETURN_PLACE && !self.mir.local_decls[mir::RETURN_PLACE].is_user_variable()
+        {
             return;
         }
 
diff --git a/src/librustc_mir/transform/nrvo.rs b/src/librustc_mir/transform/nrvo.rs
index 557ffe4a6d5..d249eaa2e43 100644
--- a/src/librustc_mir/transform/nrvo.rs
+++ b/src/librustc_mir/transform/nrvo.rs
@@ -1,3 +1,4 @@
+use rustc_hir::Mutability;
 use rustc_index::bit_set::HybridBitSet;
 use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor};
 use rustc_middle::mir::{self, BasicBlock, Local, Location};
@@ -61,6 +62,9 @@ impl<'tcx> MirPass<'tcx> for RenameReturnPlace {
             body.local_decls.pick2_mut(returned_local, mir::RETURN_PLACE);
         debug_assert_eq!(ret_decl.ty, renamed_decl.ty);
         ret_decl.clone_from(renamed_decl);
+
+        // The return place is always mutable.
+        ret_decl.mutability = Mutability::Mut;
     }
 }