feat: resolve symbol linked missing files when symlinks enabled

[stormslowly]

Why

for issue web-infra-dev/rspack#11239 (comment)
When rspack-resolver failed, the missing files were just recorded by symbol-linked paths.
In some cases, Watchpack will not emit FS change events when symbol-linked files are changed.

Solution

When a missing file is detected, add its "real" path to the missing file dependencies.
Since the file does not exist in the file system, we attempt to canonicalize it by its ancestors' path, then assemble a real path.

For example:
/root/app/node_module/lib/dist/esm/index.mjs is not existed.

/root/app/node_module/lib/ is symbol linked to real path /root/lib/

So the real path is /root/lib/dist/esm/index.mjs

We get the both symbolic path and real path in missing files in a failure resolving, so it makes watchpack to watch the right files.

[Copilot]

Pull Request Overview

This PR resolves an issue where missing files that are accessed through symbolic links are not properly tracked for file watching. When symlinks are enabled and a file resolution fails, the resolver now attempts to determine the real path of the missing file by traversing its parent directories to find an existing symlinked ancestor.

• Adds logic to resolve symbolic link paths for missing files when symlinks option is enabled
• Introduces a new is_file method that handles missing dependency tracking for symlinked files
• Replaces direct is_file calls with the new method that handles symlink resolution

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 4 comments.

File	Description
src/lib.rs	Implements symlink resolution for missing files and refactors file existence checking
src/tests/missing.rs	Adds test case for missing files in symbol-linked folders
fixtures/pnpm-workspace/packages/missing/package.json	Creates test fixture package with missing files
fixtures/pnpm-workspace/packages/app/package.json	Adds dependency on missing package for testing

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

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[Copilot]

Using unwrap() can cause panics. Consider using proper error handling or a more descriptive error message if this operation is expected to always succeed.

Suggested change

	let right_path = path.strip_prefix(ancestor).unwrap();
	return Some(real_path.join(right_path));
	if let Ok(right_path) = path.strip_prefix(ancestor) {
	return Some(real_path.join(right_path));
	}

[codspeed-hq]

CodSpeed Performance Report

Merging #109 will degrade performances by 33.48%

_{Comparing fix/missng_files_resolve_to_real (457f0ed) with main (8124bf3)}

Summary

❌ 2 regressions
✅ 3 untouched

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	resolver[resolve from symlinks multi thread]	138.3 ms	207.9 ms	-33.48%
❌	resolver[resolve from symlinks]	365.5 ms	439.9 ms	-16.91%