From 1dbed2138c75b82c1efb3a7cc2d731da9a5dda13 Mon Sep 17 00:00:00 2001
From: Protobuf Team Bot <protobuf-github-bot@google.com>
Date: Mon, 18 Mar 2024 13:43:53 -0700
Subject: [PATCH] Fix Rust Proto cpp-kernel map insertion behavior to better
 match Rust's std::HashMap and the upb-kernel behavior of "insert replaces the
 old value"

PiperOrigin-RevId: 616934577
---
 rust/cpp_kernel/cpp_api.h |  3 +++
 rust/map.rs               | 14 ++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/rust/cpp_kernel/cpp_api.h b/rust/cpp_kernel/cpp_api.h
index 409d169b31..3d82472d54 100644
--- a/rust/cpp_kernel/cpp_api.h
+++ b/rust/cpp_kernel/cpp_api.h
@@ -86,6 +86,9 @@ struct PtrAndLen {
   bool __rust_proto_thunk__Map_##rust_key_ty##_##rust_value_ty##_insert(       \
       google::protobuf::Map<key_ty, value_ty>* m, ffi_key_ty key, ffi_value_ty value) {  \
     auto iter_and_inserted = m->try_emplace(to_cpp_key, to_cpp_value);         \
+    if (!iter_and_inserted.second) {                                           \
+      iter_and_inserted.first->second = to_cpp_value;                          \
+    }                                                                          \
     return iter_and_inserted.second;                                           \
   }                                                                            \
   bool __rust_proto_thunk__Map_##rust_key_ty##_##rust_value_ty##_get(          \
diff --git a/rust/map.rs b/rust/map.rs
index 53be666973..383c76b12a 100644
--- a/rust/map.rs
+++ b/rust/map.rs
@@ -528,6 +528,20 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_overwrite_insert() {
+        let mut map: Map<i32, ProtoStr> = Map::new();
+        let mut map_mut = map.as_mut();
+        assert!(map_mut.insert(0, "fizz"));
+        // insert should return false when the key is already present
+        assert!(!map_mut.insert(0, "buzz"));
+
+        assert_that!(
+            map.as_mut().iter().collect::<Vec<_>>(),
+            unordered_elements_are![eq((0, ProtoStr::from_str("buzz"))),]
+        );
+    }
+
     #[test]
     fn test_all_maps_can_be_constructed() {
         macro_rules! gen_proto_values {