build(client): Convert mocharc-common to ESM TypeScript in mocha-test-setup and test-version-utils

[jason-ha]

Relocate mocharc-common.cjs into src/ as typed ESM TypeScript modules (mocharcCommon.ts) in both @fluid-internal/mocha-test-setup and @fluid-private/test-version-utils that now become part ot their respective build:esnext tasks.

Key changes:

• Update mocha-test-setup dependencies to have tsc depend on build:esnext
• Replace CJS require/module.exports with ESM imports and named exports
• Add FluidTestMochaConfig interface as a specific return type
• Use fs.readFileSync + JSON.parse instead of require() for package.json
• Use import.meta.dirname instead of __dirname
• Add mocharc-common-cjswrapper.cjs in mocha-test-setup for backward-compatible CJS require()
• Remove tsconfig.cjs.json_s (no longer needed) and unused tsconfig.esnext.json
• Update package.json exports maps to point to new compiled output paths
• Fix all eslint issues (strict-boolean-expressions, dot-notation, no-param-reassign, no-nodejs-modules)
• Switch .mocharc.cjs in webflow and test-version-utils packages to use getFluidTestMochaConfig from mocha-test-setup directly, as no version or layer compatibility tests are run in those packages
• Update remaining test-version-utils/mocharc-common consumers (end-to-end-tests) to ESM mocha configs (.mocharc.js since packages are type: module)

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[Copilot]

Pull request overview

This PR migrates shared Mocha configuration helpers (mocharc-common) from ad-hoc CommonJS files to typed ESM TypeScript modules in @fluid-internal/mocha-test-setup and @fluid-private/test-version-utils, updates package export maps/build wiring accordingly, and adjusts downstream .mocharc.cjs consumers to use the new entrypoints.

Changes:

• Convert mocharc-common logic to ESM TypeScript (mocharcCommon.ts) and update consumers to import/require the new exports.
• Update build wiring so the ESM build is produced as part of package build flows; remove the standalone CJS-only tsconfig in test-version-utils.
• Introduce a CJS wrapper entrypoint for @fluid-internal/mocha-test-setup/mocharc-common and update several .mocharc.cjs files to use the new sources.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
packages/test/test-version-utils/tsconfig.cjs.json	Removes the CJS-only tsconfig previously used to build compat options for Mocha config consumption.
packages/test/test-version-utils/src/mocharcCommon.ts	Adds ESM/TS implementation for generating compat-aware Mocha config.
packages/test/test-version-utils/package.json	Updates exports/scripts to point ./mocharc-common at compiled ESM output and adjusts test scripts.
packages/test/test-version-utils/mocharc-common.cjs	Deletes the legacy CJS Mocha config helper.
packages/test/test-version-utils/.mocharc.cjs	Switches to consuming Mocha config from @fluid-internal/mocha-test-setup.
packages/test/test-end-to-end-tests/.mocharc.cjs	Updates compat test Mocha config consumption to the new named export API.
packages/test/mocha-test-setup/src/mocharcCommon.ts	Converts implementation to ESM/TS, adds a typed config interface, replaces __dirname/require() usages with ESM equivalents.
packages/test/mocha-test-setup/package.json	Updates exports and build task wiring for the new ESM-based implementation and wrapper.
packages/test/mocha-test-setup/mocharc-common-cjswrapper.cjs	Adds a CJS wrapper intended to support require("@fluid-internal/mocha-test-setup/mocharc-common").
packages/service-clients/end-to-end-tests/odsp-client/src/test/.mocharc.cjs	Updates compat Mocha config consumption to new named export API.
packages/service-clients/end-to-end-tests/azure-client/src/test/.mocharc.cjs	Updates compat Mocha config consumption to new named export API.
examples/data-objects/webflow/.mocharc.cjs	Switches Mocha config source to @fluid-internal/mocha-test-setup/mocharc-common.
packages/common/client-utils/package.json	Adjusts fluidBuild.tasks dependency wiring for test/build tasks.

[CraigMacomber]

Given that https://nodejs.org/learn/typescript/run-natively exists now, it's probably practical to implement this file in typescript without a build step, and just import it directly from JS config files as a ts file.

I'm not convinced that would be better, but just pointing out it may be an option now (and wasn't recently).

[jason-ha]

That is super interesting. The docs don't comment on how existence of a .js import in a natively run .ts file are handled. The suggestion is that this aren't handled. I haven't tested that.
There are further suggestion to only employ that when using TypeScript 5.8 or later, which we aren't at yet. (Maybe in a couple months.)
So, I have #27388 out to just use TS natively, but that may not stand.

[jason-ha]

Doesn't work out - native TS is not supported for exports.
It looked like it worked, but it fails when package is used from installed package. (Can't be under node_modules.)
Locally it is also consumed from a node_modules path but that is the relative path and symbolic links resolve to a path that doesn't have node_modules.

[CraigMacomber]

I suspect this is fine, but we might want to make this file (and the others in this PR which you had to modify anyway) .mjs and just do everything we can as full ESM. Mocha has instructions for pure ESM config: https://mochajs.org/running/configuring/

[jason-ha]

Turns out the docs are quite misleading. In v12, mocha added ESM config support. But the config section is bannered by since v6. The v12 PR didn't qualify things when docs were modified.
In the end, I figured out how to use ESM config with v11 anyway. Since the config files have a single export that is the config, a "modules.exports" export that is the config.