rust: fix ICE during name resolution for impls on unit-types

The canonical paths need to support unit-types which are technically a
TupleType with no fields. This handles this case and adds an unreachable.

Fixes #3036

gcc/rust/ChangeLog:

	* resolve/rust-ast-resolve-type.cc (ResolveTypeToCanonicalPath::visit): add unit-type catch
	* resolve/rust-ast-resolve-type.h: likewise

gcc/testsuite/ChangeLog:

	* rust/compile/nr2/exclude: nr2 cant handle this
	* rust/compile/issue-3036.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

gcc/rust/resolve/rust-ast-resolve-type.cc

@@ -501,6 +501,15 @@ ResolveTypeToCanonicalPath::visit (AST::TraitObjectType &)
  rust_unreachable ();
 }
 
+void
+ResolveTypeToCanonicalPath::visit (AST::TupleType &type)
+{
+ if (!type.is_unit_type ())
+ rust_unreachable ();
+
+ result = CanonicalPath::new_seg (type.get_node_id (), "()");
+}
+
 ResolveTypeToCanonicalPath::ResolveTypeToCanonicalPath ()
  : ResolverBase (), result (CanonicalPath::create_empty ())
 {}

gcc/rust/resolve/rust-ast-resolve-type.h

@@ -246,6 +246,8 @@ class ResolveTypeToCanonicalPath : public ResolverBase
 
  void visit (AST::TraitObjectType &type) override;
 
+ void visit (AST::TupleType &type) override;
+
 private:
  ResolveTypeToCanonicalPath ();
 

gcc/testsuite/rust/compile/issue-3036.rs

@@ -0,0 +1,14 @@
+#[lang = "sized"]
+trait Sized {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Default: Sized {
+ #[stable(feature = "rust1", since = "1.0.0")]
+ fn default() -> Self;
+}
+
+impl Default for () {
+ fn default() -> () {
+ ()
+ }
+}

gcc/testsuite/rust/compile/nr2/exclude

@@ -291,3 +291,4 @@ unknown-associated-item.rs
 box_syntax_feature_gate.rs
 dropck_eyepatch_feature_gate.rs
 inline_asm_parse_output_operand.rs
+issue-3036.rs