gccrs: bug-fix implicit inference checks

When generating implicit inference variables we can miss cases where the
other side might be another inference variable too but it runs the risk of
generating unending inference cycles needing more info but if they other
side is a non general inference variables like <integer> or <float> this
is safe to do so and allows us to infer mroe cases.

Signed-off-by: Philip Herron <[email protected]>

gcc/rust/ChangeLog:

	* typecheck/rust-unify.cc (UnifyRules::go): fix inference check

Author: philberty

gcc/rust/typecheck/rust-unify.cc

@@ -153,12 +153,22 @@ UnifyRules::go ()
     {
       bool rgot_param = rtype->get_kind () == TyTy::TypeKind::PARAM;
       bool lhs_is_infer_var = ltype->get_kind () == TyTy::TypeKind::INFER;
-      bool expected_is_concrete = ltype->is_concrete () && !lhs_is_infer_var;
+      bool lhs_is_general_infer_var
+	= lhs_is_infer_var
+	  && static_cast<TyTy::InferType *> (ltype)->get_infer_kind ()
+	       == TyTy::InferType::GENERAL;
+      bool expected_is_concrete
+	= ltype->is_concrete () && !lhs_is_general_infer_var;
       bool rneeds_infer = expected_is_concrete && rgot_param;
 
       bool lgot_param = ltype->get_kind () == TyTy::TypeKind::PARAM;
       bool rhs_is_infer_var = rtype->get_kind () == TyTy::TypeKind::INFER;
-      bool receiver_is_concrete = rtype->is_concrete () && !rhs_is_infer_var;
+      bool rhs_is_general_infer_var
+	= rhs_is_infer_var
+	  && static_cast<TyTy::InferType *> (rtype)->get_infer_kind ()
+	       == TyTy::InferType::GENERAL;
+      bool receiver_is_concrete
+	= rtype->is_concrete () && !rhs_is_general_infer_var;
       bool lneeds_infer = receiver_is_concrete && lgot_param;
 
       if (rneeds_infer)