gccrs: Unit structs are not concrete when they need substitutions

Fixes #1518

gcc/rust/ChangeLog:

	* typecheck/rust-tyty.h: Fix `is_concrete` for unit types with
	substitutions.

diff --git a/gcc/rust/typecheck/rust-tyty.h b/gcc/rust/typecheck/rust-tyty.h
index 24efc7aa54c3eb4890cb98c0928b653078dd7077..43460d2dd2f3e93a57e068a36bad8a4595ac1cbb 100644 (file)
--- a/gcc/rust/typecheck/rust-tyty.h
+++ b/gcc/rust/typecheck/rust-tyty.h
@@ -1362,6 +1362,11 @@ public:
 
   bool is_concrete () const override final
   {
+    if (is_unit ())
+      {
+       return !needs_substitution ();
+      }
+
     for (auto &variant : variants)
       {
        for (auto &field : variant->get_fields ())