[COMMITTED] gccrs: Add guards against getting data from an empty vector

[Arthur Cohen]

From: Philip Herron <philip.her...@embecosm.com>

gcc/rust/ChangeLog:

        * typecheck/rust-tyctx.cc (TypeCheckContext::pop_return_type): Add
        guards around `std::vector<T>.pop_back()`.
        (TypeCheckContext::peek_context): Likewise for `std::vector<T>.back()`.

Tested on x86_64-pc-linux-gnu, committed on master.

---
 gcc/rust/typecheck/rust-tyctx.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gcc/rust/typecheck/rust-tyctx.cc b/gcc/rust/typecheck/rust-tyctx.cc
index ad5f67cc1dd..af86b064c6c 100644
--- a/gcc/rust/typecheck/rust-tyctx.cc
+++ b/gcc/rust/typecheck/rust-tyctx.cc
@@ -142,12 +142,14 @@ TypeCheckContext::push_return_type (TypeCheckContextItem 
item,
 void
 TypeCheckContext::pop_return_type ()
 {
+  rust_assert (!return_type_stack.empty ());
   return_type_stack.pop_back ();
 }
 
 TypeCheckContextItem &
 TypeCheckContext::peek_context ()
 {
+  rust_assert (!return_type_stack.empty ());
   return return_type_stack.back ().first;
 }
 
-- 
2.39.1