parser: Allow `LEFT_SHIFT` to start `parse_type`

Similarly to the last commit, we need to allow `LEFT_SHIFT` tokens to
start a qualified path type and split them into two `LEFT_ANGLE` tokens.

gcc/rust/ChangeLog:

	* parse/rust-parse-impl.h (Parser::parse_type): Allow LEFT_SHIFT to
	start a type and then split it in `parse_qualified_path_type`

gcc/testsuite/ChangeLog:

	* rust/compile/parse_associated_type_as_generic_arg3.rs: New test.

2 files changed, 70 insertions, 4 deletions

diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index 3bf26bc..2cb5e3e 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -6842,11 +6842,13 @@ Parser<ManagedTokenSource>::parse_qualified_path_type (
   if (locus == Linemap::unknown_location ())
     {
       locus = lexer.peek_token ()->get_locus ();
+
+      if (lexer.peek_token ()->get_id () == LEFT_SHIFT)
+	lexer.split_current_token (LEFT_ANGLE, LEFT_ANGLE);
+
+      // skip after somewhere?
       if (!skip_token (LEFT_ANGLE))
-	{
-	  // skip after somewhere?
-	  return AST::QualifiedPathType::create_error ();
-	}
+	return AST::QualifiedPathType::create_error ();
     }
 
   // parse type (required)
@@ -9218,6 +9220,7 @@ Parser<ManagedTokenSource>::parse_type (bool save_errors)
     case LEFT_SQUARE:
       // slice type or array type - requires further disambiguation
       return parse_slice_or_array_type ();
+    case LEFT_SHIFT:
       case LEFT_ANGLE: {
 	// qualified path in type
 	AST::QualifiedPathInType path = parse_qualified_path_in_type ();
@@ -10084,6 +10087,7 @@ Parser<ManagedTokenSource>::parse_type_no_bounds ()
     case LEFT_SQUARE:
       // slice type or array type - requires further disambiguation
       return parse_slice_or_array_type ();
+    case LEFT_SHIFT:
       case LEFT_ANGLE: {
 	// qualified path in type
 	AST::QualifiedPathInType path = parse_qualified_path_in_type ();
@@ -10597,6 +10601,7 @@ Parser<ManagedTokenSource>::parse_range_pattern_bound ()
 	return std::unique_ptr<AST::RangePatternBoundPath> (
 	  new AST::RangePatternBoundPath (std::move (path)));
       }
+    case LEFT_SHIFT:
       case LEFT_ANGLE: {
 	// qualified path in expression
 	AST::QualifiedPathInExpression path
@@ -10727,6 +10732,7 @@ Parser<ManagedTokenSource>::parse_pattern_no_alt ()
     case LEFT_SQUARE:
       // slice pattern
       return parse_slice_pattern ();
+    case LEFT_SHIFT:
       case LEFT_ANGLE: {
 	// qualified path in expression or qualified range pattern bound
 	AST::QualifiedPathInExpression path
@@ -12760,6 +12766,7 @@ Parser<ManagedTokenSource>::null_denotation (const_TokenPtr tok,
        * tokens and whatever. */
       /* FIXME: could also be path expression (and hence macro expression,
        * struct/enum expr) */
+    case LEFT_SHIFT:
       case LEFT_ANGLE: {
 	// qualified path
 	// HACK: add outer attrs to path
diff --git a/gcc/testsuite/rust/compile/parse_associated_type_as_generic_arg3.rs b/gcc/testsuite/rust/compile/parse_associated_type_as_generic_arg3.rs
new file mode 100644
index 0000000..f1cc9e7
--- /dev/null
+++ b/gcc/testsuite/rust/compile/parse_associated_type_as_generic_arg3.rs
@@ -0,0 +1,59 @@
+// { dg-additional-options "-fsyntax-only" }
+
+trait Bar {
+    type B;
+
+    fn bar();
+}
+
+trait Foo {
+    type A;
+
+    fn foo();
+}
+
+trait Toto {
+    type C;
+
+    fn toto();
+}
+
+trait Tata {
+    type D;
+    fn tata();
+}
+
+impl Toto for u32 {
+    type C = f32;
+
+    fn toto() {}
+}
+
+impl Tata for f32 {
+    type D = u32;
+
+    fn tata() {}
+}
+
+struct S;
+
+impl Bar for i32 {
+    type B = u32;
+
+    fn bar() {}
+}
+
+impl Foo for S {
+    type A = i32;
+
+    fn foo() {}
+}
+
+enum Maybe<T> {
+    Something(T),
+    Nothing,
+}
+
+fn foo() -> Maybe<<<<<S as Foo>::A as Bar>::B as Toto>::C as Tata>::D> {
+    Maybe::Something(15)
+}