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fix(turbopack): preserve resolveExtensions priority in read_matches fast path (#91856)

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### What?

Fix a bug where Turbopack ignored the priority order of
`resolveExtensions` when both a platform-specific variant (e.g.
`Component.web.tsx`) and a default variant (`Component.tsx`) exist for
the same module path. The first-listed extension should always win, but
it often didn't.

### Why?

Turbopack's `read_matches` function iterates over constant alternatives
extracted from a resolve pattern (one per extension in
`resolveExtensions`). It uses `enumerate()` to assign a priority `index`
to each alternative — lower index = higher priority — so the correct
file is picked after sorting.

The `until_end=true` branch (direct file existence check) correctly
threaded `index` through. But the `until_end=false` branch (subdirectory
descent, the path taken when the pattern contains a `/` before the
dynamic suffix) had a **hardcoded `0`** instead of `index`:

```rust
// before — all alternatives get the same priority
nested.push((0, read_matches(fs_path.clone(), ...)));

// after — priority matches the extension's position in resolveExtensions
nested.push((index, read_matches(fs_path.clone(), ...)));
```

With all alternatives at priority 0, the tie-breaking sort was
effectively arbitrary. In practice `Component.tsx` frequently beat
`Component.web.tsx` even when `.web.tsx` was listed first, breaking
platform-specific module overrides — a common React Native Web / Expo
Web pattern.

### How?

**One-line Rust fix** in
`turbopack/crates/turbopack-core/src/resolve/pattern.rs`: replace the
hardcoded `0` with the loop variable `index` in the `until_end=false`
branch of the fast path.

**Turbopack unit tests** (`turbopack-core`):
- `test_custom_extensions_web_before_default` — `.web.tsx` wins when
listed first in `resolveExtensions`
- `test_custom_extensions_fallback_when_web_missing` — correctly falls
back to `.tsx` when `.web.tsx` is absent
- Extended `test_read_matches` with `extension_ordering` and
`subpath_ordering` cases covering both the `until_end=true` and
`until_end=false` branches

**Next.js e2e test** (extended `test/e2e/app-dir/resolve-extensions/`):
- Added `PlatformComponent.web.tsx` (renders `"hello web platform"`) and
`PlatformComponent.tsx` (renders `"hello default platform"`)
- `.web.tsx` is placed before `.tsx` in `resolveExtensions` in
`next.config.js` (for both Turbopack and webpack)
- New assertion: SSR'd HTML must contain `"hello web platform"` and must
**not** contain `"hello default platform"`

Fixes #91117

- [x] Tests added. See:
https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs

---------

Co-authored-by: Tobias Koppers <[email protected]>
Co-authored-by: Claude <[email protected]>
This commit is contained in:
Tobias Koppers
2026-03-26 11:28:06 -07:00
committed by GitHub
co-authored by Tobias Koppers Claude
parent 16935744fb
commit 73e654f678
11 changed files with 195 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files
test/e2e/app-dir/resolve-extensions/app/PlatformComponent.tsx
+3
View File
@@ -0,0 +1,3 @@
export default function PlatformComponent() {
return <span>hello default platform</span>
}
test/e2e/app-dir/resolve-extensions/app/PlatformComponent.web.tsx
+3
View File
@@ -0,0 +1,3 @@
export default function PlatformComponent() {
return <span>hello web platform</span>
}
test/e2e/app-dir/resolve-extensions/app/page.jsx
+2
View File
@@ -1,12 +1,14 @@
import image from './image'
import Image from 'next/image'
import Component from './component'
import PlatformComponent from './PlatformComponent'
export default function Page() {
return (
<p>
<Image src={image} alt="hello image 1" />
<Component />
<PlatformComponent />
</p>
)
}
test/e2e/app-dir/resolve-extensions/next.config.js
+11 -1
View File
@@ -1,4 +1,14 @@
const extensions = ['', '.png', '.tsx', '.ts', '.jsx', '.js', '.json']
// .web.tsx intentionally placed before .tsx to verify resolveExtensions priority
const extensions = [
'',
'.png',
'.web.tsx',
'.tsx',
'.ts',
'.jsx',
'.js',
'.json',
]
/**
* @type {import('next').NextConfig}
test/e2e/app-dir/resolve-extensions/resolve-extensions.test.ts
+12
View File
@@ -20,4 +20,16 @@ describe('turbo-resolve-extensions', () => {
expect(text).toContain('hello world')
expect(text).toContain('hello client')
})
it('should respect resolveExtensions priority (.web.tsx before .tsx)', async () => {
// When both PlatformComponent.web.tsx and PlatformComponent.tsx exist,
// the .web.tsx variant must win because it appears first in resolveExtensions.
// This guards against a Turbopack bug where the alternative index was
// hardcoded to 0 in the fast path, collapsing all alternatives to the same
// priority and making the winner non-deterministic (usually wrong).
const res = await next.fetch('/')
const html = await res.text()
expect(html).toContain('hello web platform')
expect(html).not.toContain('hello default platform')
})
})
turbopack/crates/turbopack-core/src/resolve/mod.rs
+70 -1
View File
@@ -3469,6 +3469,7 @@ mod tests {
pattern: rcstr!("./foo.js").into(),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![("./foo.js", "foo.ts")],
})
.await;
@@ -3481,6 +3482,7 @@ mod tests {
pattern: rcstr!("./foo").into(),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![("./foo", "foo.ts")],
})
.await;
@@ -3493,6 +3495,7 @@ mod tests {
pattern: rcstr!("./posts").into(),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![("./posts", "posts.ts")],
})
.await;
@@ -3505,6 +3508,7 @@ mod tests {
pattern: rcstr!("./bar.js").into(),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![("./bar.js", "bar.js")],
})
.await;
@@ -3517,6 +3521,7 @@ mod tests {
pattern: rcstr!("./foo.ts").into(),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![("./foo.ts", "foo.ts")],
})
.await;
@@ -3530,6 +3535,7 @@ mod tests {
pattern: rcstr!("./client#frag").into(),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![("./client", "client.ts")],
})
.await;
@@ -3543,6 +3549,7 @@ mod tests {
pattern: rcstr!("./client#component.js").into(),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
// Whether or not this request key is correct somewhat ambiguous. It depends on whether
// or not we consider this fragment to be part of the request pattern
expected: vec![("./client", "client#component.ts")],
@@ -3558,6 +3565,7 @@ mod tests {
pattern: rcstr!("./page#section").into(),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![("./page", "page#section.ts")],
})
.await;
@@ -3570,6 +3578,7 @@ mod tests {
pattern: rcstr!("./client?q=s").into(),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![("./client", "client.ts")],
})
.await;
@@ -3590,6 +3599,7 @@ mod tests {
]),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![
("./src/foo.js", "src/foo.ts"),
("./src/bar.js", "src/bar.js"),
@@ -3611,6 +3621,7 @@ mod tests {
]),
enable_typescript_with_output_extension: true,
fully_specified: false,
custom_extensions: None,
expected: vec![
("./src/bar.js", "src/bar.js"),
("./src/bar", "src/bar.js"),
@@ -3627,12 +3638,61 @@ mod tests {
.await;
}
/// Test that custom `resolveExtensions` ordering is respected:
/// `.web.tsx` appears before `.tsx` in the list, so it must win when both exist.
#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
async fn test_custom_extensions_web_before_default() {
resolve_relative_request_test(TestParams {
files: vec!["Component.web.tsx", "Component.tsx"],
pattern: rcstr!("./Component").into(),
enable_typescript_with_output_extension: false,
fully_specified: false,
custom_extensions: Some(vec![
rcstr!(".web.tsx"),
rcstr!(".web.ts"),
rcstr!(".web.jsx"),
rcstr!(".web.js"),
rcstr!(".tsx"),
rcstr!(".ts"),
rcstr!(".jsx"),
rcstr!(".js"),
]),
expected: vec![("./Component", "Component.web.tsx")],
})
.await;
}
/// Test that when `.web.tsx` doesn't exist, resolution falls back to `.tsx`.
#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
async fn test_custom_extensions_fallback_when_web_missing() {
resolve_relative_request_test(TestParams {
files: vec!["Component.tsx"],
pattern: rcstr!("./Component").into(),
enable_typescript_with_output_extension: false,
fully_specified: false,
custom_extensions: Some(vec![
rcstr!(".web.tsx"),
rcstr!(".web.ts"),
rcstr!(".web.jsx"),
rcstr!(".web.js"),
rcstr!(".tsx"),
rcstr!(".ts"),
rcstr!(".jsx"),
rcstr!(".js"),
]),
expected: vec![("./Component", "Component.tsx")],
})
.await;
}
/// Parameters for resolve_relative_request_test
struct TestParams<'a> {
files: Vec<&'a str>,
pattern: Pattern,
enable_typescript_with_output_extension: bool,
fully_specified: bool,
/// Custom extensions list; when `None`, uses the default `[".ts", ".js", ".json"]`
custom_extensions: Option<Vec<RcStr>>,
expected: Vec<(&'a str, &'a str)>,
}
@@ -3643,6 +3703,7 @@ mod tests {
pattern,
enable_typescript_with_output_extension,
fully_specified,
custom_extensions,
expected,
}: TestParams<'_>,
) {
@@ -3673,6 +3734,8 @@ mod tests {
noop_backing_storage(),
));
let custom_extensions_owned = custom_extensions;
tt.run_once(async move {
#[turbo_tasks::value(transparent)]
struct ResolveRelativeRequestOutput(Vec<(String, String)>);
@@ -3683,6 +3746,7 @@ mod tests {
pattern: Pattern,
enable_typescript_with_output_extension: bool,
fully_specified: bool,
custom_extensions: Option<Vec<RcStr>>,
) -> anyhow::Result<Vc<ResolveRelativeRequestOutput>> {
let fs = DiskFileSystem::new(rcstr!("temp"), path);
let lookup_path = fs.root().owned().await?;
@@ -3692,6 +3756,7 @@ mod tests {
pattern,
enable_typescript_with_output_extension,
fully_specified,
custom_extensions,
)
.await?;
@@ -3719,6 +3784,7 @@ mod tests {
pattern,
enable_typescript_with_output_extension,
fully_specified,
custom_extensions_owned,
)
.read_strongly_consistent()
.await?;
@@ -3737,12 +3803,15 @@ mod tests {
pattern: Pattern,
enable_typescript_with_output_extension: bool,
fully_specified: bool,
custom_extensions: Option<Vec<RcStr>>,
) -> anyhow::Result<Vc<ResolveResult>> {
let request = Request::parse(pattern.clone());
let extensions = custom_extensions
.unwrap_or_else(|| vec![rcstr!(".ts"), rcstr!(".js"), rcstr!(".json")]);
let mut options_value = node_esm_resolve_options(lookup_path.clone())
.with_fully_specified(fully_specified)
.with_extensions(vec![rcstr!(".ts"), rcstr!(".js"), rcstr!(".json")])
.with_extensions(extensions)
.owned()
.await?;
options_value.enable_typescript_with_output_extension =
turbopack/crates/turbopack-core/src/resolve/pattern.rs
+94 -3
View File
@@ -1632,7 +1632,7 @@ pub async fn read_matches(
continue;
};
nested.push((
0,
index,
read_matches(
fs_path.clone(),
concat(&prefix, subpath).into(),
@@ -2662,6 +2662,8 @@ mod tests {
dynamic: Vec<String>,
dynamic_file_suffix: Vec<String>,
node_modules_dynamic: Vec<String>,
extension_ordering: Vec<String>,
subpath_ordering: Vec<String>,
}
#[turbo_tasks::function(operation)]
@@ -2704,7 +2706,7 @@ mod tests {
.collect::<Vec<_>>();
let node_modules_dynamic = read_matches(
root,
root.clone(),
rcstr!(""),
false,
Pattern::new(Pattern::Constant(rcstr!("node_modules")).or_any_nested_file()),
@@ -2714,10 +2716,57 @@ mod tests {
.map(|m| m.name().to_string())
.collect::<Vec<_>>();
// Test: extension ordering is preserved (fast path, until_end=true)
// When both Component.web.tsx and Component.tsx exist, the order of
// alternatives determines which comes first in results.
let extension_ordering = read_matches(
root.clone(),
rcstr!(""),
false,
Pattern::new(Pattern::Alternatives(vec![
Pattern::Constant(rcstr!("extensions/Component")),
Pattern::Constant(rcstr!("extensions/Component.web.tsx")),
Pattern::Constant(rcstr!("extensions/Component.tsx")),
])),
)
.await?
.into_iter()
.map(|m| m.name().to_string())
.collect::<Vec<_>>();
// Test: subpath ordering is preserved (fast path, until_end=false)
// When alternatives route to different subdirectories, the index ordering
// must be respected. This exercises the fix for the hardcoded `0` bug.
let subpath_ordering = read_matches(
root.clone(),
rcstr!(""),
false,
Pattern::new({
let mut p = Pattern::Alternatives(vec![
Pattern::Concatenation(vec![
Pattern::Constant(rcstr!("prio/a/")),
Pattern::Dynamic,
]),
Pattern::Concatenation(vec![
Pattern::Constant(rcstr!("prio/b/")),
Pattern::Dynamic,
]),
]);
p.normalize();
p
}),
)
.await?
.into_iter()
.map(|m| m.name().to_string())
.collect::<Vec<_>>();
Ok(ReadMatchesOutput {
dynamic,
dynamic_file_suffix,
node_modules_dynamic,
extension_ordering,
subpath_ordering,
}
.cell())
}
@@ -2727,7 +2776,25 @@ mod tests {
// node_modules shouldn't be matched by Dynamic here
assert_eq!(
matches.dynamic,
&["index.js", "sub", "sub/", "sub/foo-a.js", "sub/foo-b.js"]
&[
"extensions",
"extensions/",
"extensions/Component.tsx",
"extensions/Component.web.tsx",
"index.js",
"prio",
"prio/",
"prio/a",
"prio/a/",
"prio/a/Component.tsx",
"prio/b",
"prio/b/",
"prio/b/Component.tsx",
"sub",
"sub/",
"sub/foo-a.js",
"sub/foo-b.js",
]
);
// basic dynamic file suffix
@@ -2740,6 +2807,30 @@ mod tests {
// want to enumerate the list of packages here.
assert_eq!(matches.node_modules_dynamic, &["node_modules"]);
// extension ordering: .web.tsx (index 1) must come before .tsx (index 2)
assert_eq!(
matches.extension_ordering,
&["extensions/Component.web.tsx", "extensions/Component.tsx",]
);
// subpath ordering: prio/a/ alternatives (index 0) must come before prio/b/
// alternatives (index 1). This verifies the fix for the hardcoded `0` bug in
// the until_end=false branch of the fast path.
assert!(
matches
.subpath_ordering
.iter()
.position(|s| s.starts_with("prio/a/"))
.unwrap()
< matches
.subpath_ordering
.iter()
.position(|s| s.starts_with("prio/b/"))
.unwrap(),
"Expected prio/a/ results before prio/b/ results, got: {:?}",
matches.subpath_ordering
);
Ok(())
})
.await
turbopack/crates/turbopack-core/tests/pattern/read_matches/extensions/Component.tsx
View File
turbopack/crates/turbopack-core/tests/pattern/read_matches/extensions/Component.web.tsx
View File
turbopack/crates/turbopack-core/tests/pattern/read_matches/prio/a/Component.tsx
View File
turbopack/crates/turbopack-core/tests/pattern/read_matches/prio/b/Component.tsx
View File