[gccrs COMMIT] gccrs: add null guard for failed builtin expansion

[gerris.rs@gmail.com]

From: Philip Herron <herron.philip@googlemail.com>

Fixes Rust-GCC/gccrs#4477

gcc/rust/ChangeLog:

	* expand/rust-expand-visitor.cc (builtin_derive_item): check for null and remove

Signed-off-by: Philip Herron <herron.philip@googlemail.com>
---
This change was merged into the gccrs repository and is posted here for
upstream visibility and potential drive-by review, as requested by GCC
release managers.
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Commit on github: https://github.com/Rust-GCC/gccrs/commit/3b0b57e0033f4198e492abcdbd65c00d83c734ae

The commit has been mentioned in the following issue(s):
 - Rust-GCC/gccrs#4477: https://github.com/Rust-GCC/gccrs/issues/4477

The commit has been mentioned in the following pull-request(s):
 - https://github.com/Rust-GCC/gccrs/pull/4895

 gcc/rust/expand/rust-expand-visitor.cc | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/gcc/rust/expand/rust-expand-visitor.cc b/gcc/rust/expand/rust-expand-visitor.cc
index 3a042ac9a..e78f72305 100644
--- a/gcc/rust/expand/rust-expand-visitor.cc
+++ b/gcc/rust/expand/rust-expand-visitor.cc
@@ -49,13 +49,22 @@ static std::vector<std::unique_ptr<AST::Item>>
 builtin_derive_item (AST::Item &item, const AST::Attribute &derive,
 		     BuiltinMacro to_derive, MacroExpander &expander)
 {
+  auto &mappings = Analysis::Mappings::get ();
   auto item_source = AST::Builder::get_item_source (expander.crate);
 
   auto items
     = AST::DeriveVisitor::derive (item, derive, to_derive, item_source);
 
-  for (auto &item : items)
-    Analysis::Mappings::get ().add_derived_node (item->get_node_id ());
+  for (auto it = items.begin (); it != items.end ();)
+    {
+      if (*it == nullptr)
+	it = items.erase (it);
+      else
+	{
+	  mappings.add_derived_node ((*it)->get_node_id ());
+	  ++it;
+	}
+    }
 
   return items;
 }

base-commit: 883e65a539a9c84c6cb29f19ddca1bca47daf163
-- 
2.55.0