From a67fbe6a687871036be0631261eb494d40557cc8 Mon Sep 17 00:00:00 2001
From: Adrian Taylor <adetaylor@chromium.org>
Date: Thu, 15 Jun 2023 10:30:42 +0100
Subject: [PATCH] Fix reference wrappers + mutable refs problem.

Fixes #1294.
---
 engine/src/conversion/type_helpers.rs | 58 +++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 engine/src/conversion/type_helpers.rs

diff --git a/engine/src/conversion/type_helpers.rs b/engine/src/conversion/type_helpers.rs
new file mode 100644
index 000000000..8eb3a3a23
--- /dev/null
+++ b/engine/src/conversion/type_helpers.rs
@@ -0,0 +1,58 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use syn::{
+    AngleBracketedGenericArguments, GenericArgument, PathArguments, PathSegment, Type, TypePath,
+    TypeReference,
+};
+
+/// Looks in a `core::pin::Pin<&mut Something>` and returns the `Something`
+/// if it's found.
+/// This code could _almost_ be used from various other places around autocxx
+/// but they each have slightly different requirements. Over time we should
+/// try to migrate other instances to use this, though.
+pub(crate) fn extract_pinned_mutable_reference_type(tp: &TypePath) -> Option<&Type> {
+    if !is_pin(tp) {
+        return None;
+    }
+    if let Some(PathSegment {
+        arguments: PathArguments::AngleBracketed(AngleBracketedGenericArguments { args, .. }),
+        ..
+    }) = tp.path.segments.last()
+    {
+        if args.len() == 1 {
+            if let Some(GenericArgument::Type(Type::Reference(TypeReference {
+                mutability: Some(_),
+                elem,
+                ..
+            }))) = args.first()
+            {
+                return Some(elem);
+            }
+        }
+    }
+    None
+}
+
+/// Whether this type path is a `Pin`
+fn is_pin(tp: &TypePath) -> bool {
+    if tp.path.segments.len() != 3 {
+        return false;
+    }
+    static EXPECTED_SEGMENTS: &[&[&str]] = &[&["std", "core"], &["pin"], &["Pin"]];
+
+    for (seg, expected_name) in tp.path.segments.iter().zip(EXPECTED_SEGMENTS.iter()) {
+        if !expected_name
+            .iter()
+            .any(|expected_name| seg.ident == expected_name)
+        {
+            return false;
+        }
+    }
+    true
+}