[gcc r14-7307] gccrs: bug-fix implicit inference checks

[Arthur Cohen]

https://gcc.gnu.org/g:49d5df4c826e14beaa9ee4c01c8fb710bd81a7bb

commit r14-7307-g49d5df4c826e14beaa9ee4c01c8fb710bd81a7bb
Author: Philip Herron <herron.philip@googlemail.com>
Date:   Mon Feb 27 17:39:09 2023 +0000

    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 <herron.philip@googlemail.com>
    
    gcc/rust/ChangeLog:
    
            * typecheck/rust-unify.cc (UnifyRules::go): fix inference check

Diff:
---
 gcc/rust/typecheck/rust-unify.cc | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/gcc/rust/typecheck/rust-unify.cc b/gcc/rust/typecheck/rust-unify.cc
index dcd1783c29a..3af261db59e 100644
--- a/gcc/rust/typecheck/rust-unify.cc
+++ b/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)