fix: copy raw binary to dist/index.wasm during standalone builds, not base64

[alfonso-noriega]

WHY are these changes introduced?

Community regression (CLI 3.93.0): after shopify app build, dist/index.wasm contains base64-encoded text instead of raw binary, causing vitest to fail immediately when loading the wasm.

---

How the bug was introduced — the full chain

There are two independent concerns that outputPath has been confusingly conflating:

Concern	Meaning
Local build output path	Where the compiler writes the wasm on disk (configured via build.path in TOML, e.g. target/wasm32-wasi/release/my_func.wasm)
Bundle destination path	Where the wasm lands inside the deploy artifact (always dist/index.wasm — a hard server-side contract)

1. Commit 4446834 (bad refactor): changed getOutputRelativePath to return build.path ?? dist/index.wasm. This caused extension.outputPath at construction time to point at the compiler output path, which meant the wasm ended up under the wrong key in the deploy bundle — breaking all Function deploys.

2. PR #7085 (fix, Mar 24): restored getOutputRelativePath to always return dist/index.wasm. This fixed deploys. However, it also means extension.outputPath starts as <project>/dist/index.wasm again. Inside buildFunctionExtension:

bundlePath = extension.outputPath          // ← <project>/dist/index.wasm
extension.outputPath = <project>/<build.path>  // mutated to compiler output
// build runs, raw wasm at <project>/<build.path>
if bundlePath !== extension.outputPath && dirname differs:
    bundleFunctionExtension(...)           // ← writes BASE64 to <project>/dist/index.wasm ✗

When called from shopify app build (i.e. ext.build() directly), bundlePath is the project's own dist/index.wasm, so base64 is written straight into the developer's project.

3. PR #7161 (partial fix, Apr 2): added a dirname check to skip bundling when build.path is in the same directory as dist/ (e.g. dist/custom.wasm). This helps only that narrow case. Typical Rust functions have build.path = "target/wasm32-wasi/release/func.wasm" — a completely different directory — so the base64 encoding still runs.

4. Community report (Apr 7): users on CLI 3.93.0 see vitest fail because dist/index.wasm has base64 text, not raw WASM bytes.

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Why the same code works correctly for shopify app deploy

When called from buildForBundle (the deploy path), buildForBundle pre-sets extension.outputPath to the temp bundle directory before calling build():

// in buildForBundle:
this.outputPath = this.getOutputPathForDirectory(bundleDirectory, outputId)
//   = <appDir>/.shopify/deploy-bundle/<id>/dist/index.wasm  ← bundle dir, not project
await this.build(options)

So inside buildFunctionExtension, bundlePath = <bundleDir>/dist/index.wasm (outside the project), and the base64 encoding goes into the bundle directory — exactly right for the zip upload. The project's dist/index.wasm is never touched.

The problem is that shopify app build skips buildForBundle and calls ext.build() directly, so bundlePath is the project's own dist/index.wasm.

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WHAT is this pull request doing?

Adds a check in buildFunctionExtension to distinguish between the two call sites using a simple, unambiguous condition:

const projectOutputPath = joinPath(extension.directory, extension.outputRelativePath)
// projectOutputPath is always <project>/dist/index.wasm

if (bundlePath === projectOutputPath) {
  // Standalone build — copy raw binary so vitest and local tooling can load the wasm
  await copyFile(extension.outputPath, bundlePath)
} else if (dirname(bundlePath) !== dirname(extension.outputPath)) {
  // Deploy bundle build — base64-encode for the server contract
  await bundleFunctionExtension(extension.outputPath, bundlePath)
}

Scenario	bundlePath	Behaviour
shopify app build (standalone)	<project>/dist/index.wasm	Raw binary copied → vitest works ✓
shopify app deploy / buildForBundle	<bundleDir>/<id>/dist/index.wasm	Base64 encoded → server contract satisfied ✓
build.path = dist/custom.wasm (same dir, standalone)	<project>/dist/index.wasm	Raw binary copied from dist/custom.wasm → dist/index.wasm ✓
build.path = dist/custom.wasm (same dir, bundle)	<bundleDir>/<id>/dist/index.wasm	Base64 encoded → server contract satisfied ✓

How to test your changes?

1. Create a Rust function extension with a custom build.path pointing to the Cargo output:

   [build]
   command = "cargo wasi build --release"
   path = "target/wasm32-wasi/release/my_func.wasm"

2. Run shopify app build — verify dist/index.wasm is raw binary (e.g. starts with \0asm magic bytes), not base64 text.
3. Run your vitest suite — verify function tests pass.
4. Run shopify app deploy — verify the function deploys successfully (wasm uploaded under dist/index.wasm).
5. Run shopify app dev — verify dev draft updates work correctly.

Measuring impact

• n/a — bug fix for a confirmed community regression; no new behaviour surface

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes

[alfonso-noriega]

• fix: copy raw binary to dist/index.wasm during standalone builds, not base64 #7237 👈 (View in Graphite)
• main

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