Allow --module bundler --moduleResolution commonjs

[andrewbranch]

Prerequisite for #62200

This has worked in a coherent way since --module preserve was implemented, but was prohibited with a program error. --moduleResolution bundler (like every other modern TS resolution mode) resolves package.json "exports" conditions according to the output module syntax being emitted. So in --module commonjs, imports in .ts and .js files always resolve with the "require" condition set.

This combination of settings is very rarely going to be what people actually want, and is mostly intended as a "my code works, don't bother me" upgrade path for users on --module commonjs --moduleResolution: node. (More poignantly, it doesn't seem like deprecating --module commonjs is an option at this point, and with --moduleResolution node10 going away, that leaves no moduleResolution settings left that are legal with commonjs.) However, it's also the correct settings for anyone transpiling their code to CommonJS before resolving imports through a bundler. This includes Webpack ts-loader users who have --module commonjs in their ts-loader tsconfig. However, you should not use this combination of settings just because you set your bundler's output to emit a CommonJS module, so our docs / blog post need to be intentional about highlighting this.

[Copilot]

Pull Request Overview

This PR allows the combination of --module bundler with --moduleResolution commonjs, which was previously prohibited with a program error. This change supports users who transpile their TypeScript code to CommonJS before bundling, particularly those using tools like Webpack's ts-loader with CommonJS module compilation settings.

Key changes:

• Removes the restriction preventing --moduleResolution bundler from being used with --module commonjs
• Updates error messages to include "commonjs" as a valid module option with bundler resolution
• Adds comprehensive test coverage for the new combination of settings

Reviewed Changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/compiler/program.ts	Updates validation logic to allow --module commonjs with --moduleResolution bundler
src/compiler/diagnosticMessages.json	Updates error message text to include "commonjs" as a valid option
tests/cases/conformance/moduleResolution/bundler/bundlerCommonJS.ts	New test file demonstrating CommonJS module resolution with bundler
tests/cases/conformance/moduleResolution/bundler/bundlerOptionsCompat.ts	Updates existing test to use "nodenext" instead of "commonjs"
Multiple baseline files	Updates test baselines to reflect the new allowed combination and updated error messages

[andrewbranch]

As of #57896 (TS 5.6), .mts and .cts extensions override the --module setting. Since this import will emit as an import, and the package has only a require entrypoint, the resolution fails.