From da75d07632927fa952f3c748bd2cfcfbc5d1fe1d Mon Sep 17 00:00:00 2001
From: Pablo Rivas <5464238+elkhantar@users.noreply.github.com>
Date: Thu, 2 Jul 2026 10:54:51 +0200
Subject: [PATCH] Compile the QuickJS module on the instantiating runtime

Runtime.CompileModule bakes the compiling runtime's store-assigned
function type IDs into the CompiledModule. Since wazero v1.12, import
resolution compares those numeric IDs (required for the GC proposal's
concrete ref types) rather than structural signatures, so a module
compiled on the global throwaway runtime fails to instantiate on the
per-New runtime with 'signature mismatch' on identical-looking
signatures (wazero <= v1.11 compared structurally and tolerated this).

Compiling on the instantiating runtime assigns consistent type IDs.
The machine code is shared through the CompilationCache held in
cachedRuntimeConfig, so the per-runtime compile is a cache hit.
---
 runtime.go | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/runtime.go b/runtime.go
index f099bc3..6de84a6 100644
--- a/runtime.go
+++ b/runtime.go
@@ -132,12 +132,30 @@ func New(options ...Option) (runtime *Runtime, err error) {
 		return nil, fmt.Errorf("failed to setup host module: %w", err)
 	}
 
+	// Compile on this runtime rather than reusing the globally compiled
+	// module: CompileModule bakes the compiling Runtime's store-assigned
+	// function type IDs into the CompiledModule, and since wazero v1.12
+	// import resolution compares those numeric IDs (needed for the GC
+	// proposal's concrete ref types) instead of structural signatures.
+	// Instantiating a module compiled on another Runtime therefore fails
+	// with "signature mismatch" on identical-looking signatures. The
+	// machine code is shared through the CompilationCache held in
+	// cachedRuntimeConfig, so this per-runtime compile is a cache hit.
+	qjsBytes := wasmBytes
+	if len(option.QuickJSWasmBytes) > 0 {
+		qjsBytes = option.QuickJSWasmBytes
+	}
+	localCompiled, err := runtime.wrt.CompileModule(option.Context, qjsBytes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to compile qjs module: %w", err)
+	}
+
 	fsConfig := wazero.
 		NewFSConfig().
 		WithDirMount(runtime.option.CWD, "/")
 	if runtime.module, err = runtime.wrt.InstantiateModule(
 		option.Context,
-		compiledQJSModule,
+		localCompiled,
 		wazero.NewModuleConfig().
 			WithStartFunctions(option.StartFunctionName).
 			WithSysWalltime().