[gcc r14-7673] gccrs: we can't check the bounds involving empty placeholder types

[gcc r14-7673] gccrs: we can't check the bounds involving empty placeholder types

[Arthur Cohen]

https://gcc.gnu.org/g:0f15c111397bedbc0b01c65aa9cb477d65af53fe

commit r14-7673-g0f15c111397bedbc0b01c65aa9cb477d65af53fe
Author: Philip Herron <herron.philip@googlemail.com>
Date:   Wed Jun 14 12:11:38 2023 +0100

    gccrs: we can't check the bounds involving empty placeholder types
    
    We use placeholders for assoicated types on traits but if we are unifying
    types against a placeholder its not possible to check the bounds as the
    placeholder does not have enough information yet at this point to determine
    if bounds will or won't be satisfied. That check will occur when associated
    types and generics are setup.
    
    Fixes #2036
    
    gcc/rust/ChangeLog:
    
            * typecheck/rust-unify.cc (UnifyRules::go): dont check bounds on placeholders
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/issue-2036.rs: New test.
    
    Signed-off-by: Philip Herron <herron.philip@googlemail.com>

Diff:
---
 gcc/rust/typecheck/rust-unify.cc         |  6 +++++-
 gcc/testsuite/rust/compile/issue-2036.rs | 36 ++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/gcc/rust/typecheck/rust-unify.cc b/gcc/rust/typecheck/rust-unify.cc
index 42e10950917..0e62a21dc25 100644
--- a/gcc/rust/typecheck/rust-unify.cc
+++ b/gcc/rust/typecheck/rust-unify.cc
@@ -151,7 +151,11 @@ UnifyRules::go ()
 	      rtype->debug_str ().c_str ());
 
   // check bounds
-  bool should_check_bounds = !ltype->is_equal (*rtype);
+  bool ltype_is_placeholder = ltype->get_kind () == TyTy::TypeKind::PLACEHOLDER;
+  bool rtype_is_placeholder = rtype->get_kind () == TyTy::TypeKind::PLACEHOLDER;
+  bool types_equal = ltype->is_equal (*rtype);
+  bool should_check_bounds
+    = !types_equal && !(ltype_is_placeholder || rtype_is_placeholder);
   if (should_check_bounds)
     {
       if (ltype->num_specified_bounds () > 0)
diff --git a/gcc/testsuite/rust/compile/issue-2036.rs b/gcc/testsuite/rust/compile/issue-2036.rs
new file mode 100644
index 00000000000..d1459752ea5
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-2036.rs
@@ -0,0 +1,36 @@
+trait Hash<H> {
+    fn hash2(&self, hasher: &H) -> u64;
+}
+
+trait Stream {
+    fn input(&mut self, bytes: &[u8]);
+    fn result(&self) -> u64;
+}
+
+trait StreamHasher {
+    type S: Stream;
+    fn stream(&self) -> Self::S;
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+trait StreamHash<H: StreamHasher>: Hash<H> {
+    fn input_stream(&self, stream: &mut H::S);
+}
+
+impl<H: StreamHasher> Hash<H> for u8 {
+    fn hash2(&self, hasher: &H) -> u64 {
+        let mut stream = hasher.stream();
+        self.input_stream(&mut stream);
+        // { dg-error "type annotations needed" "" { target *-*-* } .-1 }
+        Stream::result(&stream)
+    }
+}
+
+impl<H: StreamHasher> StreamHash<H> for u8 {
+    fn input_stream(&self, stream: &mut H::S) {
+        Stream::input(stream, &[*self]);
+    }
+}
+
+fn main() {}