gccrs: fix segfault in clone_pattern w macro

Check if parser throw an error to avoid cloning nullptr

Fixes #4140

gcc/rust/ChangeLog:

	* expand/rust-macro-expand.cc (transcribe_expression): check if
	parser didn't fail
	(transcribe_type): check if parser didn't fail
	(transcribe_pattern): check if parser didn't fail

Signed-off-by: lenny.chiadmi-delage <lenny.chiadmi-delage@epita.fr>

Author: Villosse

gcc/rust/expand/rust-macro-expand.cc

@@ -962,12 +962,10 @@ transcribe_expression (Parser<MacroInvocLexer> &parser)
 
   auto attrs = parser.parse_outer_attributes ();
   auto expr = parser.parse_expr (std::move (attrs));
-  if (expr == nullptr)
-    {
-      for (auto error : parser.get_errors ())
-	error.emit ();
-      return AST::Fragment::create_error ();
-    }
+  for (auto error : parser.get_errors ())
+    error.emit ();
+  if (!expr)
+    return AST::Fragment::create_error ();
 
   // FIXME: make this an error for some edititons
   if (parser.peek_current_token ()->get_id () == SEMICOLON)
@@ -997,6 +995,8 @@ transcribe_type (Parser<MacroInvocLexer> &parser)
   auto type = parser.parse_type (true);
   for (auto err : parser.get_errors ())
     err.emit ();
+  if (!type)
+    return AST::Fragment::create_error ();
 
   auto end = lexer.get_offs ();
 
@@ -1018,6 +1018,9 @@ transcribe_pattern (Parser<MacroInvocLexer> &parser)
   for (auto err : parser.get_errors ())
     err.emit ();
 
+  if (!pattern)
+    return AST::Fragment::create_error ();
+
   auto end = lexer.get_offs ();
 
   return AST::Fragment ({std::move (pattern)},