Implement selective typecheck

[sgb-io]

Selective TypeCheck

• Implements selective typecheck, i.e adds the --ancestors, --descendants, --changed and --compareBranch options to modular typecheck
• Maintains backwards compatibility with the existing modular typecheck
• Adds new docs that describe how Modular currently treats tsconfig.json files, plus docs for the new options
• Updates the tests for typecheck to use a new approach, and cover new cases

New unit testing approach: calling commands directly

A side mission during this PR was to call typecheck() directly from test code, instead of rely on execa as is very common in the project. The execa approach is (a) slow and (b) breaks the tracking of test coverage. typecheck.test.ts demonstrates a new approach:

• Call the command directly, avoiding the need for a child process, and fixing jest's ability to track test coverage
• Mock getModularRoot in tests, which is used extensively throughout the project
• Create a secondary getModularRoot clone called getRealModularRootInTest that is designed to be used in test code, i.e. avoid any mocks that might be applicable
• Avoid the actionPreflightCheck, which complicates the mocking (it contains a call to getModularRoot) and slows things down. Plus, this check has no value in test (it can be tested in isolation).

It should be noted that I've used jest.doMock which avoids jest's default hoisting behaviour. In other words, it lets us mock the modular root just before importing and calling a modular command. To work with this approach, I dynamically import the typecheck command. It may also be possible to use a more static setup.

Not only is this approach faster and simpler, the coverage for the test command has gone from 0 to >90%.

TODO

• New docs
• Repoint PR to v4.3 or main when v4.2 is released
• Tests
• Changeset

[changeset-bot]

🦋 Changeset detected

Latest commit: 4ae9bcc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
modular-scripts	Minor

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[coveralls]

Coverage: 23.335% (+2.9%) from 20.414% when pulling 4ae9bcc on sgb-io:feat/selective-typecheck into 2c25504 on jpmorganchase:feature/v4.3.

[sgb-io]

This block is currently uncovered, worth adding a test case for it (essentially, using the jsx option)

[sgb-io]

This is a bugfix. The second argument was previously reading tsconfig.json from the cwd(), since no modular root was being used. This is not consistent with the first argument, where the modular root is used.

That said, in practice, there was no actual way for users to be affected by this bug - since commands are supposed to be run in the root already (so not using the modular root resulted in the correct file being used), and preflight errors actually get in the way first if you try to run something like typecheck from the non-root dir.

The bugfix here is needed so that we can effectively test the code in test, i.e. use a faked modular root and have it respected.