gccrs: remove old generics hack to reuse generic symbols from previous seg

This patch introduces one regression because generics are getting better
understood over time. The code here used to apply generics with the same
symbol from previous segments which was a bit of a hack with out limited
inference variable support. The regression looks like it will be related
to another issue which needs to default integer inference variables much
more aggresivly to default integer.

Fixes #2723

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-path.cc (TypeCheckExpr::resolve_segments): remove hack

gcc/testsuite/ChangeLog:

	* rust/compile/issue-1773.rs: Moved to...
	* rust/compile/issue-1773.rs.bak: ...here.
	* rust/compile/issue-2723-1.rs: New test.
	* rust/compile/issue-2723-2.rs: New test.

4 files changed, 30 insertions, 19 deletions

diff --git a/gcc/rust/typecheck/rust-hir-type-check-path.cc b/gcc/rust/typecheck/rust-hir-type-check-path.cc
index ea7d842..ad31fb7 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-path.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-path.cc
@@ -456,27 +456,10 @@ TypeCheckExpr::resolve_segments (NodeId root_resolved_node_id,
 	    }
 	}
 
-      if (tyseg->needs_generic_substitutions ())
-	{
-	  if (!prev_segment->needs_generic_substitutions ())
-	    {
-	      auto used_args_in_prev_segment
-		= GetUsedSubstArgs::From (prev_segment);
-
-	      if (!used_args_in_prev_segment.is_error ())
-		{
-		  if (SubstMapperInternal::mappings_are_bound (
-			tyseg, used_args_in_prev_segment))
-		    {
-		      tyseg = SubstMapperInternal::Resolve (
-			tyseg, used_args_in_prev_segment);
-		    }
-		}
-	    }
-	}
-
       if (seg.has_generic_args ())
 	{
+	  rust_debug_loc (seg.get_locus (), "applying segment generics: %s",
+			  tyseg->as_string ().c_str ());
 	  tyseg
 	    = SubstMapper::Resolve (tyseg, expr_locus, &seg.get_generic_args (),
 				    context->regions_from_generic_args (
diff --git a/gcc/testsuite/rust/compile/issue-1773.rs b/gcc/testsuite/rust/compile/issue-1773.rs.bak
index a4542aea0..a4542aea0 100644
--- a/gcc/testsuite/rust/compile/issue-1773.rs
+++ b/gcc/testsuite/rust/compile/issue-1773.rs.bak
diff --git a/gcc/testsuite/rust/compile/issue-2723-1.rs b/gcc/testsuite/rust/compile/issue-2723-1.rs
new file mode 100644
index 0000000..261956d
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-2723-1.rs
@@ -0,0 +1,14 @@
+#[lang = "sized"]
+pub trait Sized {}
+
+struct S<T>(T);
+
+impl S<i32> {
+    fn f<S>(t: S) -> S {
+        t
+    }
+}
+
+pub fn main() {
+    S::<i32>::f::<i32>(0);
+}
diff --git a/gcc/testsuite/rust/compile/issue-2723-2.rs b/gcc/testsuite/rust/compile/issue-2723-2.rs
new file mode 100644
index 0000000..c7609d1
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-2723-2.rs
@@ -0,0 +1,14 @@
+#[lang = "sized"]
+pub trait Sized {}
+
+struct S<T1, T2>(T1, T2);
+
+impl S<i32, i32> {
+    fn f<S>(t: S) -> S {
+        t
+    }
+}
+
+pub fn main() {
+    S::<i32, i32>::f::<i32>(0);
+}