[alexander-akait]

Summary

Compiling a schema at runtime loads ajv. That costs about 150 ms for the first schema of a process, plus a few to tens of milliseconds for each later one, and every loader and plugin that validates its options pays it on every start.

This adds:

• schema-utils precompile [--check] <schema.json>...: compiles a schema ahead of time into <schema>.check.js next to it. --check writes nothing and fails when a check is missing or out of date, for CI.
• A check fourth argument to validate(schema, options, configuration, check): a valid value is only checked and ajv is never loaded. An invalid value still runs the full validation, so the error messages are unchanged.
• precompile(schema, { loadSchema }): the same as an API. It returns the module source and is loaded lazily from the main entry.

validate(schema, options, { name: "CSS Loader" }, require("./options.check.js"));

Details

• instanceof, absolutePath and undefinedAsNull are compiled with functions at runtime, which ajv standalone can't emit. They get code-generating twins with the same semantics. undefinedAsNull also sets undefined to null in the parent, as the full validation does.
• The generated module loads the ajv runtime helpers it needs (equal, ucs2length, uri, formats) through schema-utils/dist/runtime. The packages shipping a check depend on schema-utils, not on ajv. Each helper is a getter, so only the ones a schema uses get loaded.
• Annotations (title, description, link, …) are stripped before compiling. The file: URLs of the compiled and loaded schemas are made relative, so the output is the same on every machine. A file: URL that is a schema value is left alone.
• The output starts with /* eslint-disable */ and // @ts-nocheck so consumers don't lint or type-check generated code. It is CommonJS.

Measurements

Node 22, fresh process, packed tarball installed into a scratch project, css-loader's options.json:

	validate(schema, options)	validate(schema, options, config, check)
First validation	~150–160 ms	~8 ms
Error message for invalid options	the full one	identical
ajv core loaded for valid options	yes	no

For css-loader, style-loader and minimizer-webpack-plugin together: ~280 ms with ajv at runtime against ~12 ms precompiled.

Tests

• Every pass and fail case in test/index.test.js (about 400 cases, including the webpack schema) also runs the precompiled check and must agree. Pass cases must also leave the same value behind, which covers undefinedAsNull.
• New tests in test/precompile.test.js cover validate with a check, the keywords, external $ref, path relativizing, the runtime helpers and the CLI.
• Outside the suite, I compiled all of webpack's schemas/**/*.json with the CLI. The resulting WebpackOptions check agrees with webpack's committed one on all 3,698 configs from webpack's configCases, watchCases and hotCases.

Follow-ups (separate PRs)

• webpack: this.getOptions(schema, check) for loaders, and switching tooling/precompile-schemas.js to this command.
• eslint-config-webpack: a webpack/require-precompiled-schema rule.
• Precompiling in minimizer-webpack-plugin and the webpack-contrib loaders and plugins.

🤖 Generated with Claude Code

https://claude.ai/code/session_01QYPkbvwyRWt2SHgXDoYRdo

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Generated by Claude Code

Summary by CodeRabbit

• New Features
  • Added command-line and programmatic schema precompilation to generate standalone checks that report whether values are valid.
  • validate accepts an optional precompiled check, avoiding schema compilation when values pass and retaining standard validation errors when they don’t.
  • Added a CLI check mode that flags missing or outdated generated checks. Precompilation supports external schema references, including custom loading options. The CLI can process multiple schemas and reports failures for individual files.

[codecov]

Codecov Report

❌ Patch coverage is 99.41860% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 97.11%. Comparing base (c9e4796) to head (5cfcea2).

Files with missing lines	Patch %	Lines
src/precompile.js	99.03%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #231      +/-   ##
==========================================
+ Coverage   96.72%   97.11%   +0.38%     
==========================================
  Files          10       13       +3     
  Lines        1009     1180     +171     
  Branches      415      457      +42     
==========================================
+ Hits          976     1146     +170     
- Misses         31       32       +1     
  Partials        2        2              

Flag	Coverage Δ
integration	97.11% <99.41%> (+0.38%)	⬆️

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ℹ️ Recent review info

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📒 Files selected for processing: 1

• bin/schema-utils.js

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• bin/schema-utils.js

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Walkthrough

Adds an API to compile schemas into standalone CommonJS checks and an optional check parameter to validate. Adds a CLI to generate checks or report missing and outdated files. The precompiler supports file-based references by default and accepts a custom loader for other external references. Tests cover generated checks, validation behavior, and CLI commands.

Priority: ➖ Normal

Merge Risk: ⚪ Minimal · up to 5ddce

Failed precompilation now returns a nonzero exit status, so the selected change is ready to merge after normal checks.

Pre-merge checks: 5

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: adding schema precompilation that produces a check for validate.
Docstring Coverage		Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 18 functions across 15 files.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: Organization UI
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• Run ID: cfb06bdb-e125-4bbf-a633-73ea834668d3

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Reviewing files that changed from the base of the PR and between c9e4796 and 149a247.

📒 Files selected for processing: 18

• .changeset/precompiled-schemas.md
• README.md
• bin/schema-utils.js
• declarations/cli.d.ts
• declarations/index.d.ts
• declarations/precompile.d.ts
• declarations/runtime.d.ts
• declarations/validate.d.ts
• eslint.config.mjs
• package.json
• src/cli.js
• src/index.js
• src/precompile.js
• src/runtime.js
• src/validate.js
• test/helpers/precompiled.js
• test/index.test.js
• test/precompile.test.js

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