From b9baa79b4dc277501f860325da34403b89fb4ee9 Mon Sep 17 00:00:00 2001
From: Zeeshan Lakhani <zeeshan@oxidecomputer.com>
Date: Sat, 7 Nov 2026 01:55:46 +0000
Subject: [PATCH] [codegen, fix] Replace (not insert) table entries with
 matching keys

`HashSet::insert` retained the prev entry, which meant that adding the
same key with a new action or new params was a no-op. We now use replace
per @rcgoodfellow @ oxidecomputer/dendrite#405.
---
 codegen/rust/src/pipeline.rs |  4 +++-
 test/src/mcast.rs            | 28 ++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/codegen/rust/src/pipeline.rs b/codegen/rust/src/pipeline.rs
index 4bca914e..a73e601e 100644
--- a/codegen/rust/src/pipeline.rs
+++ b/codegen/rust/src/pipeline.rs
@@ -1000,9 +1000,11 @@ impl<'a> PipelineGenerator<'a> {
                             #(#parameter_refs),*
                         )
                     });
+                    // Upserting an entry replaces any previous entry with a
+                    // matching key
                     self.#tname
                         .entries
-                        .insert(p4rs::table::TableEntry::<
+                        .replace(p4rs::table::TableEntry::<
                             #n,
                             std::sync::Arc<dyn Fn(
                                 #(#control_param_types),*
diff --git a/test/src/mcast.rs b/test/src/mcast.rs
index b72044b6..3976a3db 100644
--- a/test/src/mcast.rs
+++ b/test/src/mcast.rs
@@ -282,6 +282,34 @@ fn bitmap_ports_beyond_radix_ignored() -> Result<(), anyhow::Error> {
     Ok(())
 }
 
+#[test]
+fn upserting_key_replaces_action_and_params() {
+    let mut pipeline = main_pipeline::new(4);
+    let key = 0u16.to_le_bytes();
+
+    pipeline.add_ingress_bitmap_table_entry(
+        "set_bitmap",
+        &key,
+        &port_bitmap(16, &[1, 2]),
+        0,
+    );
+    pipeline.add_ingress_bitmap_table_entry(
+        "set_bitmap",
+        &key,
+        &port_bitmap(16, &[3]),
+        0,
+    );
+    assert_egress_ports(&mut pipeline, 0, &[3]);
+
+    pipeline.add_ingress_bitmap_table_entry(
+        "forward",
+        &key,
+        &1u16.to_le_bytes(),
+        0,
+    );
+    assert_egress_ports(&mut pipeline, 0, &[1]);
+}
+
 fn unicast_mac(port: u16) -> [u8; 6] {
     let id = 0x20 + port as u8;
     [0x02, 0x00, id, id, 0x00, 0x02]