gccrs: Fix memory corruption at peek_context

When working in the resolve_operator_overload it was found that we got
memory corruption as method resolution will use the query system and
therefore resolve new methods and the current function context info will
change and due to the fact the peek_context interface returns a reference
to the element which was now safe from a vector which can change and all
you need is the current function context at that moment in time.

gcc/rust/ChangeLog:

	* typecheck/rust-autoderef.cc: don't take a reference
	* typecheck/rust-hir-type-check-expr.cc (TypeCheckExpr::visit): likewise
	* typecheck/rust-hir-type-check.h: remove reference
	* typecheck/rust-typecheck-context.cc (TypeCheckContext::pop_return_type): likewise

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

4 files changed, 5 insertions, 5 deletions

diff --git a/gcc/rust/typecheck/rust-autoderef.cc b/gcc/rust/typecheck/rust-autoderef.cc
index 90a67ed62f2..078a5705b56 100644
--- a/gcc/rust/typecheck/rust-autoderef.cc
+++ b/gcc/rust/typecheck/rust-autoderef.cc
@@ -164,7 +164,7 @@ resolve_operator_overload_fn (
   // handle the case where we are within the impl block for this
   // lang_item otherwise we end up with a recursive operator overload
   // such as the i32 operator overload trait
-  TypeCheckContextItem &fn_context = context->peek_context ();
+  TypeCheckContextItem fn_context = context->peek_context ();
   if (fn_context.get_type () == TypeCheckContextItem::ItemType::IMPL_ITEM)
     {
       auto &impl_item = fn_context.get_impl_item ();
diff --git a/gcc/rust/typecheck/rust-hir-type-check-expr.cc b/gcc/rust/typecheck/rust-hir-type-check-expr.cc
index f8ac63266a8..f205a49e707 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-expr.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-expr.cc
@@ -1457,7 +1457,7 @@ TypeCheckExpr::visit (HIR::MatchExpr &expr)
 void
 TypeCheckExpr::visit (HIR::ClosureExpr &expr)
 {
-  TypeCheckContextItem &current_context = context->peek_context ();
+  TypeCheckContextItem current_context = context->peek_context ();
   TyTy::FnType *current_context_fndecl = current_context.get_context_type ();
 
   HirId ref = expr.get_mappings ().get_hirid ();
@@ -1624,7 +1624,7 @@ TypeCheckExpr::resolve_operator_overload (
   // handle the case where we are within the impl block for this lang_item
   // otherwise we end up with a recursive operator overload such as the i32
   // operator overload trait
-  TypeCheckContextItem &fn_context = context->peek_context ();
+  TypeCheckContextItem fn_context = context->peek_context ();
   if (fn_context.get_type () == TypeCheckContextItem::ItemType::IMPL_ITEM)
     {
       auto &impl_item = fn_context.get_impl_item ();
diff --git a/gcc/rust/typecheck/rust-hir-type-check.h b/gcc/rust/typecheck/rust-hir-type-check.h
index 62fd8f3ddee..ec63657aaa6 100644
--- a/gcc/rust/typecheck/rust-hir-type-check.h
+++ b/gcc/rust/typecheck/rust-hir-type-check.h
@@ -90,7 +90,7 @@ public:
   bool lookup_type_by_node_id (NodeId ref, HirId *id);
 
   TyTy::BaseType *peek_return_type ();
-  TypeCheckContextItem &peek_context ();
+  TypeCheckContextItem peek_context ();
   void push_return_type (TypeCheckContextItem item,
 			 TyTy::BaseType *return_type);
   void pop_return_type ();
diff --git a/gcc/rust/typecheck/rust-typecheck-context.cc b/gcc/rust/typecheck/rust-typecheck-context.cc
index 8bca751e788..7a40fc8313b 100644
--- a/gcc/rust/typecheck/rust-typecheck-context.cc
+++ b/gcc/rust/typecheck/rust-typecheck-context.cc
@@ -157,7 +157,7 @@ TypeCheckContext::pop_return_type ()
   return_type_stack.pop_back ();
 }
 
-TypeCheckContextItem &
+TypeCheckContextItem
 TypeCheckContext::peek_context ()
 {
   rust_assert (!return_type_stack.empty ());