From ddf65fc2deb996dd504b3f355e5891749776f0f4 Mon Sep 17 00:00:00 2001
From: Tim Smart <hello@timsmart.co>
Date: Thu, 20 Aug 2026 19:39:27 +0000
Subject: [PATCH] Stop SchemaBinary leaking into encoding barrel consumers

`EMPTY_READER_VIEW` was built from `EMPTY_READER_BUFFER.buffer`. A member
access in argument position is not effect-free to a bundler, so the
`@__PURE__` annotation the build adds could not be honoured and the pair
survived tree shaking in every consumer that imports
`effect/unstable/encoding` without ever touching this module. Both
placeholders now read one named `ArrayBuffer`, which keeps
`EMPTY_READER_VIEW.buffer === EMPTY_READER_BUFFER.buffer` exactly as
before.

Add a tracked bundle fixture so the module's size is compared on every
PR by the existing Bundle job.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 .../effect/src/unstable/encoding/SchemaBinary.ts | 16 +++++++++++-----
 packages/tools/bundle/fixtures/schema-binary.ts  | 10 ++++++++++
 2 files changed, 21 insertions(+), 5 deletions(-)
 create mode 100644 packages/tools/bundle/fixtures/schema-binary.ts

diff --git a/packages/effect/src/unstable/encoding/SchemaBinary.ts b/packages/effect/src/unstable/encoding/SchemaBinary.ts
index 4c7a3d1cd1d..7f3099f7b15 100644
--- a/packages/effect/src/unstable/encoding/SchemaBinary.ts
+++ b/packages/effect/src/unstable/encoding/SchemaBinary.ts
@@ -542,8 +542,14 @@ class IndexSignatureCache {
   }
 }
 
-const EMPTY_READER_BUFFER = new Uint8Array(0)
-const EMPTY_READER_VIEW = new DataView(EMPTY_READER_BUFFER.buffer)
+// Both placeholders read the same named `ArrayBuffer` rather than reaching
+// through `EMPTY_READER_BUFFER.buffer`. A member access in argument position
+// defeats the `@__PURE__` annotation the build adds, which pinned this pair
+// into the bundle of every consumer that imports the encoding barrel without
+// ever touching this module.
+const EMPTY_READER_ARRAY_BUFFER = new ArrayBuffer(0)
+const EMPTY_READER_BUFFER = new Uint8Array(EMPTY_READER_ARRAY_BUFFER)
+const EMPTY_READER_VIEW = new DataView(EMPTY_READER_ARRAY_BUFFER)
 const EMPTY_PARSE_OPTIONS: SchemaAST.ParseOptions = {}
 
 class Reader {
@@ -2384,9 +2390,9 @@ function decodeExtraPair(layout: StructLayout, r: Reader, out: Record<string, un
 }
 
 // Both wire modes report a missing required field the same way: one
-// `MissingKey` per field under a `Pointer` to its name, collected into a
-// `Composite`. Only `errors: "all"` decides whether the first one stops the
-// decode.
+// `MissingKey` under a `Pointer` to its name. The call sites accumulate them
+// and `throwMissingKeys` wraps the batch in a `Composite`; only
+// `errors: "all"` decides whether the first one stops the decode.
 function missingKeyIssue(field: Field): SchemaIssue.Issue {
   return new SchemaIssue.Pointer([field.name], new SchemaIssue.MissingKey(field.annotations))
 }
diff --git a/packages/tools/bundle/fixtures/schema-binary.ts b/packages/tools/bundle/fixtures/schema-binary.ts
new file mode 100644
index 00000000000..49a3dc84f92
--- /dev/null
+++ b/packages/tools/bundle/fixtures/schema-binary.ts
@@ -0,0 +1,10 @@
+import * as Schema from "effect/Schema"
+import * as SchemaBinary from "effect/unstable/encoding/SchemaBinary"
+
+const schema = Schema.Struct({
+  a: Schema.String,
+  b: Schema.optional(Schema.FiniteFromString),
+  c: Schema.Array(Schema.String)
+})
+
+export const codec = SchemaBinary.toCodec(schema)