perf(package-requester): pickFetcher runs eagerly for every resolved package after #12491

[zkochan]

Summary

PR #12491 moved the pickFetcher call in resolveAndFetch (pnpm11/installing/package-requester/src/packageRequester.ts) so that it now runs eagerly for every resolved package, before the skip-fetch early return:

const fetcherForResolution = resolution.type === 'variations'
  ? undefined
  : await pickFetcher(ctx.fetchers, resolution as AtomicResolution, {
    customFetchers: ctx.customFetchers,
    packageId: id,
  })

Previously pickFetcher ran lazily, only inside the actual download path (fetcher()), i.e. only on a store cache miss. Now it is invoked once per resolved package regardless of whether the package is:

• a store cache hit (the bulk of a warm-cache install),
• skipped via --lockfile-only / skipFetch, or
• not installable on the current platform (optional deps for another OS).

Impact

For each of those packages the install now pays for:

• classifyResolution(), which does a .toLowerCase() URL classification per tarball resolution, and
• with custom-fetcher hooks configured, an await customFetcher.canFetch(...) per custom fetcher per package — potentially expensive async work that previously only ran on cache misses.

This is a small, hot-path inefficiency. It is not a measured regression in the current pacquet Bencher suite (the registry-mock fixtures are small and it stays within noise), but it is unnecessary work on large real-world installs, especially with custom fetchers.

Proposed fix

Only select a fetcher eagerly when its resolutionNeedsFetch signal can actually be non-false: when custom fetchers are present, or for a tarball-shaped resolution (resolution.type == null) whose integrity is missing. Otherwise leave fetcherForResolution undefined and let the fetch path pick lazily on a cache miss (the pre-#12491 behavior). variations must continue to never go through pickFetcher.

A working patch (verified against the package-requester test suite, 27/27 passing) gates the call like this:

const customFetchers = ctx.customFetchers
const hasCustomFetchers = customFetchers != null && customFetchers.length > 0
let fetcherForResolution: PickedFetcher | undefined
let resolutionNeedsFetch = false
if (
  resolution.type !== 'variations' &&
  (hasCustomFetchers || (resolution.type == null && getExpectedIntegrity(resolution) == null))
) {
  fetcherForResolution = await pickFetcher(ctx.fetchers, resolution as AtomicResolution, {
    customFetchers,
    packageId: id,
  })
  const resolutionNeedsFetchHook = fetcherForResolution.resolutionNeedsFetch
  resolutionNeedsFetch = typeof resolutionNeedsFetchHook === 'function'
    ? resolutionNeedsFetchHook(resolution)
    : false
}

This keeps the common registry-tarball-with-integrity path off the pickFetcher path entirely, while preserving the integrity-population behavior #12491 added (integrity-less remote tarballs still set resolutionNeedsFetch).

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Written by an agent (Claude Code, claude-opus-4-8).