From 3d4aeddb82d94f78692c4fe125bee413c0dec9e3 Mon Sep 17 00:00:00 2001
From: Chris Tate <chris@ctate.dev>
Date: Sat, 24 Oct 2026 17:03:27 -0500
Subject: [PATCH] Keep the reply scanner in a constant object

A native build of a program that installs the C scanner but decodes no
reply, such as the self-hosted source parser and CommonJS checks, failed
at startup with "Cannot access 'valueEnd' before initialization": the
build left the module variable uninitialized because its only other use
was the assignment in useNativeJsonValueEnd, which checks it first.

The scanner is now a property of a constant object that the decoders
and useNativeJsonValueEnd read, so it is initialized in every program.
---
 .../compiler/src/frontend/ts7/semantic-json.ts  | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/packages/compiler/src/frontend/ts7/semantic-json.ts b/packages/compiler/src/frontend/ts7/semantic-json.ts
index 1a4d93bd6..8913007d3 100644
--- a/packages/compiler/src/frontend/ts7/semantic-json.ts
+++ b/packages/compiler/src/frontend/ts7/semantic-json.ts
@@ -104,15 +104,20 @@ export function jsonValueEnd(bytes: Uint8Array, start: number): number {
 }
 
 /** The scanner the decoders find value ends with: jsonValueEnd, or the
- * native compiler's scanner (useNativeJsonValueEnd). */
-let valueEnd: (bytes: Uint8Array, start: number) => number = jsonValueEnd;
+ * native compiler's scanner (useNativeJsonValueEnd). It is a property of a
+ * constant object: a program that installs the scanner but decodes no
+ * reply must still initialize it, and an assigned module variable with no
+ * other reader would be left uninitialized by a native build. */
+const scanner: { valueEnd: (bytes: Uint8Array, start: number) => number } = {
+  valueEnd: jsonValueEnd,
+};
 
 /** Has the decoders find value ends with `scan`, which returns what
  * jsonValueEnd returns, or -1 where jsonValueEnd throws. The native compiler
  * installs its C scanner (native/ts7-process.c), which skips the strings that
  * make up most reply bytes with memchr. */
 export function useNativeJsonValueEnd(scan: (bytes: Uint8Array, start: number) => number): void {
-  valueEnd = (bytes, start) => {
+  scanner.valueEnd = (bytes, start) => {
     const end = scan(bytes, start);
     if (end < 0) malformedReply();
     return end;
@@ -174,7 +179,7 @@ export function decodeSemanticObject<T extends { id: number }, R>(
 ): R | null {
   const start = skipJsonSpace(bytes, 0);
   if (start === bytes.length) return null;
-  const end = valueEnd(bytes, start);
+  const end = scanner.valueEnd(bytes, start);
   if (skipJsonSpace(bytes, end) !== bytes.length) malformedReply();
   return replyElement(bytes, start, end, cached, build);
 }
@@ -190,7 +195,7 @@ export function decodeSemanticObjects<T extends { id: number }, R>(
   let index = skipJsonSpace(bytes, 0);
   if (index === bytes.length) return null;
   if (bytes[index] !== OPEN_BRACKET) {
-    const end = valueEnd(bytes, index);
+    const end = scanner.valueEnd(bytes, index);
     if (
       skipJsonSpace(bytes, end) !== bytes.length ||
       parseJsonSlice<null>(bytes, index, end) !== null
@@ -205,7 +210,7 @@ export function decodeSemanticObjects<T extends { id: number }, R>(
     return result;
   }
   for (;;) {
-    const end = valueEnd(bytes, index);
+    const end = scanner.valueEnd(bytes, index);
     if (end === index) malformedReply();
     result.push(replyElement(bytes, index, end, cached, build));
     index = skipJsonSpace(bytes, end);