[gcc/devel/rust/master] gccrs: bug-fix implicit inference checks

[Thomas Schwinge <tschwinge@gcc.gnu.org>]

https://gcc.gnu.org/g:a20426036a360d781dae2361ffd4c7dcfe4bb40a

commit a20426036a360d781dae2361ffd4c7dcfe4bb40a
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 e76b362aa0c..fb7b5d4bd6f 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)