From 1ad628a18eda3714b83c69c05ab994dcbac6d8b8 Mon Sep 17 00:00:00 2001
From: Ryan Roden-Corrent <ryan@rcorre.net>
Date: Tue, 16 Jan 2024 08:41:33 -0500
Subject: [PATCH] Default to packed repeated primitive fields in proto3.

Fixes #704.

In proto3, repeated primitive fields should be packed by default:
https://protobuf.dev/programming-guides/encoding/#packed
---
 protobuf-codegen/src/gen/field/mod.rs | 31 ++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/protobuf-codegen/src/gen/field/mod.rs b/protobuf-codegen/src/gen/field/mod.rs
index d6a5e44a4..79a16e05e 100644
--- a/protobuf-codegen/src/gen/field/mod.rs
+++ b/protobuf-codegen/src/gen/field/mod.rs
@@ -188,7 +188,36 @@ impl<'a> FieldGen<'a> {
 
                 FieldKind::Repeated(RepeatedField {
                     elem,
-                    packed: field.field.proto().options.get_or_default().packed(),
+                    packed: field
+                        .field
+                        .proto()
+                        .options
+                        .get_or_default()
+                        .packed
+                        .unwrap_or(match field.message.scope.file_scope.syntax() {
+                            Syntax::Proto2 => false,
+                            // in proto3, repeated primitive types are packed by default
+                            Syntax::Proto3 => match field.field.proto().type_() {
+                                Type::TYPE_DOUBLE
+                                | Type::TYPE_FLOAT
+                                | Type::TYPE_INT64
+                                | Type::TYPE_UINT64
+                                | Type::TYPE_INT32
+                                | Type::TYPE_FIXED64
+                                | Type::TYPE_FIXED32
+                                | Type::TYPE_BOOL
+                                | Type::TYPE_UINT32
+                                | Type::TYPE_SFIXED32
+                                | Type::TYPE_SFIXED64
+                                | Type::TYPE_SINT32
+                                | Type::TYPE_SINT64 => true,
+                                Type::TYPE_STRING
+                                | Type::TYPE_GROUP
+                                | Type::TYPE_MESSAGE
+                                | Type::TYPE_BYTES
+                                | Type::TYPE_ENUM => false,
+                            },
+                        }),
                 })
             }
             RuntimeFieldType::Singular(..) => {