gccrs: Add validation pass for label name

Prevent from using reserved keyword in label name.

gcc/rust/ChangeLog:

	* ast/rust-ast-visitor.cc (DefaultASTVisitor::visit): Check if there is
	a label before visit.
	* checks/errors/rust-ast-validation.cc (ASTValidation::visit): Emit an
	error when a label has a forbidden name.
	* checks/errors/rust-ast-validation.h: Add function prototype.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

gcc/rust/ast/rust-ast-visitor.cc

@@ -494,7 +494,9 @@ void
 DefaultASTVisitor::visit (AST::BreakExpr &expr)
 {
   visit_outer_attrs (expr);
-  visit (expr.get_label ());
+  if (expr.has_label ())
+    visit (expr.get_label ());
+
   if (expr.has_break_expr ())
     visit (expr.get_break_expr ());
 }

gcc/rust/checks/errors/rust-ast-validation.cc

@@ -36,6 +36,21 @@ ASTValidation::visit (AST::Lifetime &lifetime)
   AST::ContextualASTVisitor::visit (lifetime);
 }
 
+void
+ASTValidation::visit (AST::LoopLabel &label)
+{
+  auto name = label.get_lifetime ().get_lifetime_name ();
+  auto lifetime_name = '\'' + name;
+  auto &keywords = Values::Keywords::keywords;
+  if (keywords.find (name) != keywords.end ())
+    rust_error_at (label.get_locus (), "invalid label name %qs",
+		   lifetime_name.c_str ());
+
+  // WARNING: Do not call ContextualASTVisitor, we don't want to visit the
+  // lifetime
+  // Maybe we should refactor LoopLabel instead ?
+}
+
 void
 ASTValidation::visit (AST::ConstantItem &const_item)
 {

gcc/rust/checks/errors/rust-ast-validation.h

@@ -35,6 +35,7 @@ public:
 
   virtual void visit (AST::ConstantItem &const_item);
   virtual void visit (AST::Lifetime &lifetime);
+  virtual void visit (AST::LoopLabel &label);
 };
 
 } // namespace Rust