feat(bundle-size-tools): emit and consume analyzer.json for bundle size diff

[ChumpChief]

Description

webpack-bundle-analyzer's analyzerMode: "json" output (analyzer.json) is a much smaller, pre-summarized form of the per-asset data we use for bundle-size comparisons (~750KB vs ~3.7MB for bundleStats.msp.gz, the compressed raw stats we currently consume — and ~377MB raw). We use roughly 1% of what's in the full webpack stats. Switching to analyzer.json lets us drop the entire WebpackStatsProcessor pipeline (gunzip → msgpack-decode → walk → entry processor → total processor) and just read pre-summarized per-asset parsedSize directly.

Two commits, separable for review:

1. Producer (examples/utils/bundle-size-tests/webpack.config.cjs): adds a second BundleAnalyzerPlugin instance with analyzerMode: "json", emitting bundleAnalysis/analyzer.json alongside the existing report.html/report.json/bundleStats.msp.gz. Existing outputs are unchanged — flub generate bundleStats sanity checks and the FF-internal telemetry handler keep working as-is.
2. Consumer (bundle-size-tools): adds analyzer.json reader functions (getAnalyzerJsonFromZip, getAnalyzerJsonFromFileSystem), path discovery (getAnalyzerFilePathsFromFolder and the getAnalyzerPathsFrom* wrappers), and getBundleSummariesFromAnalyzer. ADOSizeComparator switches to the analyzer.json path internally. result.json shape and BundleMetric (parsedSize-only) are unchanged, and per-entrypoint metric names/values match between the two paths. One delta: the msp.gz path's synthesized per-bundle "Total Size" metric is no longer emitted (it's derivable from the per-asset metrics if a downstream consumer needs it).

The new readers use BundleAnalyzerPlugin.JsonReport from @types/webpack-bundle-analyzer (added as a devDep) so the type comes from the producer authoritatively rather than a hand-rolled subset.

Public-API surface is purely additive — the prior msp.gz reader path (getStatsFileFromZip, getStatsFileFromFileSystem, getBundleSummaries with its original args, getBundleFilePathsFromFolder's msp.gz detection, DefaultStatsProcessors, etc.) remains exported and functional. It just goes unused by ADOSizeComparator after this change.

A follow-up PR will clean up the now-dead code (the msp.gz reader path, the WebpackStatsProcessor infrastructure, and related types). It was left out of this PR to keep the review focused on the swap itself.

Part of AB#56981 (re-enable PR bundle size comparison) — this is one of several incremental PRs that will follow PR #27158.

[github-actions]

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Based on the diff (235 lines, 11 files), I've queued these reviewers:

• Correctness — logic errors, race conditions, lifecycle issues
• Security — vulnerabilities, secret exposure, injection
• API Compatibility — breaking changes, release tags, type design
• Performance — algorithmic regressions, memory leaks
• Testing — coverage gaps, hollow tests

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[github-actions]

On it! Starting review with: Correctness, Security, API Compatibility

[github-actions]

🔭 PR Review Fleet Report

Note

This report is generated by an experimental AI review fleet and is provided as a beta feature. Findings are a starting point for discussion, not a gate. Use your own judgement.

Verdict: ❌ Request Changes

0 Exterminate, 1 Squash, 2 Investigate

Findings

Sev	#	Area	File	What	Fix
🦟 Squash	H1	API Compatibility	build-tools/packages/bundle-size-tools/package.json:57	BundleAnalyzerPlugin.JsonReport from @types/webpack-bundle-analyzer is exposed directly in three public API signatures — the return types of getAnalyzerJsonFromFileSystem and getAnalyzerJsonFromZip, and the getAnalyzerJson property type of GetBundleSummariesFromAnalyzerArgs. However, @types/webpack-bundle-analyzer is listed only in devDependencies, so it will not be installed when a consumer installs this package. Any TypeScript consumer that references these APIs will fail to resolve the BundleAnalyzerPlugin namespace, producing compile errors.	Either move @types/webpack-bundle-analyzer from devDependencies to dependencies, or avoid leaking the external type in the public surface by defining a local structural alias (e.g. export type AnalyzerJsonReport = { label: string; parsedSize: number; isAsset?: boolean; ... }[]) and using that in the public signatures instead.
🐜 Investigate	M1	API Compatibility	build-tools/packages/bundle-size-tools/src/ADO/getBundleFilePathsFromFolder.ts:60	getAnalyzerFilePathsFromFolder returns BundleFileData[] and populates the relativePathToStatsFile field with paths to analyzer.json files. The field name relativePathToStatsFile implies webpack stats output, not webpack-bundle-analyzer JSON output. Consumers reading IntelliSense on the returned objects will be misled about what the field contains, especially since getBundleSummariesFromAnalyzer then passes bundle.relativePathToStatsFile directly to getAnalyzerJson, hiding the semantic mismatch behind an unrelated field name.	Add a dedicated field to BundleFileData (e.g. relativePathToAnalyzerFile?: string) for analyzer.json paths, or introduce a separate AnalyzerFileData type. This keeps the data shape self-documenting and avoids conflating two different file formats under one field name.
🐜 Investigate	M2	API Compatibility	build-tools/packages/bundle-size-tools/src/ADO/getBundleSummaries.ts:297	GetBundleSummariesFromAnalyzerArgs is @public (undocumented) — neither the interface nor its two properties (bundlePaths, getAnalyzerJson) carry JSDoc. A consumer reading IntelliSense on getBundleSummariesFromAnalyzer cannot tell what contract getAnalyzerJson must satisfy (error handling, whether the path is relative or absolute, expected JSON shape) or what bundlePaths should contain.	Add JSDoc to the interface and both properties, documenting the path convention (relative vs. absolute), the expected JSON shape, and error-handling expectations. This is consistent with how the existing GetBundleSummariesArgs should also be documented, but the new interface should not add to the undocumented surface.

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[ChumpChief]

I'm planning to skip the Fleet feedback as these will all become internal and/or change further in the followups. Primary goal of this PR is just to start producing the analyzer.json which is more generally useful.

[Copilot]

Pull request overview

This PR updates the bundle size diff pipeline to produce and consume webpack-bundle-analyzer’s analyzerMode: "json" output (analyzer.json) as a smaller, pre-summarized input for bundle size comparisons, while keeping the legacy bundleStats.msp.gz path exported for now.

Changes:

• Emit bundleAnalysis/analyzer.json during bundle-size test builds (alongside existing HTML/JSON stats outputs).
• Add analyzer.json discovery + readers and a new getBundleSummariesFromAnalyzer() path in @fluidframework/bundle-size-tools.
• Switch ADOSizeComparator to use analyzer.json summaries instead of the bundleStats.msp.gz/stats-processor pipeline.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
examples/utils/bundle-size-tests/webpack.config.cjs	Adds a second BundleAnalyzerPlugin instance to emit analyzer.json alongside existing artifacts.
build-tools/pnpm-lock.yaml	Locks the newly added @types/webpack-bundle-analyzer dependency.
build-tools/packages/bundle-size-tools/src/index.ts	Re-exports new analyzer.json APIs from the package entrypoint.
build-tools/packages/bundle-size-tools/src/ADO/index.ts	Re-exports new analyzer.json APIs from the ADO sub-entrypoint.
build-tools/packages/bundle-size-tools/src/ADO/getBundleSummaries.ts	Introduces getBundleSummariesFromAnalyzer() and related args type.
build-tools/packages/bundle-size-tools/src/ADO/getBundleFilePathsFromFolder.ts	Adds getAnalyzerFilePathsFromFolder() for analyzer.json discovery.
build-tools/packages/bundle-size-tools/src/ADO/FileSystemBundleFileProvider.ts	Adds filesystem path discovery + JSON parsing for analyzer.json.
build-tools/packages/bundle-size-tools/src/ADO/AdoSizeComparator.ts	Switches comparator implementation to analyzer.json-based summaries.
build-tools/packages/bundle-size-tools/src/ADO/AdoArtifactFileProvider.ts	Adds zip path discovery + JSON parsing for analyzer.json.
build-tools/packages/bundle-size-tools/package.json	Adds @types/webpack-bundle-analyzer (devDependency).
build-tools/packages/bundle-size-tools/api-report/bundle-size-tools.api.md	Updates API report to include newly exported analyzer.json APIs/types.

Files not reviewed (1)

• build-tools/pnpm-lock.yaml: Language not supported