Regression - TypeScript watch attempts to watch parent directory files

[jack-guy]

TypeScript Version: 3.0.0-dev.20180526

Search Terms: TypeScript, Watch, Hang

Code

Repo with reproduction

Steps

1. clone repository
2. cd linked-package, yarn, tsc
3. cd main, yarn
4. Add breakpoints to watchFailedLookupLocationOfResolution, run compiler in watch mode in /main to see that the values of dir and dirPath will cause watchers to be added to files in the reproduction directory, including the unrelated-package folder. I do this using vscode - here's a demonstration video.

I haven't been able to exactly narrow down what is causing this behavior, but it seems to have a few necessary components:

1. A symlinked module dependency
2. That symlinked module dependency exports from another file
3. That symlinked module has a scoped name (e.g. @scoped/linked-package) - less sure about this one

Expected behavior:
In TypeScript 2.7, watchers aren't added for this parent directory. This behavior is introduced in TypeScript 2.8 and remains in the latest 3.0 versions.

There shouldn't be a module lookup failure in this case and file watchers should not be added outside the confines of the directory where the compiler is run.

Actual behavior:
I first discovered this behavior when running Typescript 2.8 on a pretty large project of mine. While the build was completing without issue, when I tried to watch for changes the CLI got stuck on "Starting compilation in watch mode..."

I diagnosed the issue by issuing a SIGUSR1 to the typescript process to start a debugger and found that TypeScript was adding file watchers to all the directories in foo/ where my project was in foo/a/ and used a module foo/b/. Since foo/ is my personal development directory with many, many JavaScript projects, the compiler was effectively hanging indefinitely.

I noticed that if I remove the symlinked module's export and inlined its code (in the reproduction export * from './other';), the module lookup no longer fails.

[mhegazy]

@sheetalkamat can you take a look.

[jack-guy]

@sheetalkamat Thanks for fixing this so quickly!!