From 02f146c1ff0e29cadf072fc60f443d4913174189 Mon Sep 17 00:00:00 2001
From: Dave Nagoda <dave.nagoda@shopify.com>
Date: Tue, 30 Jun 2026 15:07:14 -0700
Subject: [PATCH] Preserve JSON input object order

Function-runner parses JSON inputs into serde_json::Value and reserializes them before passing bytes to the WASM. With serde_json's default map implementation, this sorts object keys lexicographically, which can change JS behavior that depends on Object.keys() ordering for fallback logic.\n\nEnable serde_json's preserve_order feature so JSON input object key order is retained, and add a regression test covering nested metafield-like message objects. This keeps function-rerunner parity closer to production inputs for Checkout Blocks discount functions.\n\nVerified with:\n- cargo test json_input_preserves_object_key_order_in_raw_bytes\n- cargo build --release\n- cargo test\n- Rerunning the 17 discount localized-message mismatch rows with the fixed release runner produced full semantic matches.

Assisted-By: devx/c659e918-9568-4750-b122-e3890447348a
---
 Cargo.lock       |  1 +
 Cargo.toml       |  2 +-
 src/container.rs | 15 +++++++++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/Cargo.lock b/Cargo.lock
index ee10bd6f..238c0d10 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2588,6 +2588,7 @@ version = "1.0.149"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "83fc039473c5595ace860d8c4fafa220ff474b3fc6bfdb4293327f1a37e94d86"
 dependencies = [
+ "indexmap",
  "itoa",
  "memchr",
  "serde",
diff --git a/Cargo.toml b/Cargo.toml
index fb59981d..6b0ffc5f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -50,7 +50,7 @@ wasmtime-wasi = "=39.0.1"
 deterministic-wasi-ctx = "=3.0.4"
 anyhow = "1.0"
 clap = { version = "4.5", features = ["derive"] }
-serde_json = "1.0"
+serde_json = { version = "1.0", features = ["preserve_order"] }
 colored = "3.1"
 serde = "1.0"
 rust-embed = "8.11.0"
diff --git a/src/container.rs b/src/container.rs
index c3c1fd1b..435bf729 100644
--- a/src/container.rs
+++ b/src/container.rs
@@ -136,3 +136,18 @@ impl BytesContainer {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn json_input_preserves_object_key_order_in_raw_bytes() {
+        let raw = br#"{"msg":{"sq-XK":"5.00 EUR Zbritje","en":"5.00 EUR Discount"}}"#.to_vec();
+
+        let input = BytesContainer::new(BytesContainerType::Input, Codec::Json, raw.clone())
+            .expect("valid JSON input");
+
+        assert_eq!(String::from_utf8(input.raw).unwrap(), String::from_utf8(raw).unwrap());
+    }
+}