gccrs: Fix SEGV when type path resolver fails outright

When we resolve paths we resolve to Types first we walk each segment to
the last module which has no type but then in the event that the child
of a module is not found we have a null root_tyty which needs to be caught
and turned into an ErrorType node.

Fixes Rust-GCC#3613

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-type.cc (TypeCheckType::resolve_root_path):
	catch nullptr root_tyty

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3613.rs: New test.

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

2 files changed, 25 insertions, 0 deletions

diff --git a/gcc/rust/typecheck/rust-hir-type-check-type.cc b/gcc/rust/typecheck/rust-hir-type-check-type.cc
index e56fa39..54f50ec 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-type.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-type.cc
@@ -360,6 +360,13 @@ TypeCheckType::resolve_root_path (HIR::TypePath &path, size_t *offset,
 			     seg->as_string ().c_str ());
 	      return new TyTy::ErrorType (path.get_mappings ().get_hirid ());
 	    }
+	  else if (root_tyty == nullptr)
+	    {
+	      rust_error_at (seg->get_locus (),
+			     "unknown reference for resolved name: %qs",
+			     seg->as_string ().c_str ());
+	      return new TyTy::ErrorType (path.get_mappings ().get_hirid ());
+	    }
 	  return root_tyty;
 	}
 
diff --git a/gcc/testsuite/rust/compile/issue-3613.rs b/gcc/testsuite/rust/compile/issue-3613.rs
new file mode 100644
index 0000000..f2e1092
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-3613.rs
@@ -0,0 +1,18 @@
+mod m1 {
+    pub enum Baz4 {
+        foo1,
+        foo2,
+    }
+}
+
+fn bar(x: m1::foo) {
+    // { dg-error "unknown reference for resolved name: .foo." "" { target *-*-* } .-1 }
+    match x {
+        m1::foo::foo1 => {}
+        // { dg-error "failed to type resolve root segment" "" { target *-*-* } .-1 }
+        m1::NodePosition::foo2 => {}
+        // { dg-error "failed to type resolve root segment" "" { target *-*-* } .-1 }
+    }
+}
+
+pub fn main() {}