Allow for multiple root directories when scanning for fence files

[Adjective-Object]

Motivation

In owa, we currently rely on excluding the node_modules directory.

This works fine under current usage, but BuildXL by convention stores state in the Out directory, which stores unique logs across multiple runs -- this was causing good-fences to take upwards of 20 minutes on subsequent runs.

By specifying the rootDirs as packages and shared instead of relying on traversing from the common directory ., we speed up good-fences (and avoid transient read errors caused by files being deleted out from under good-fences as it traverses BuildXL's internal state).

Changes

• changes rootDir to an array of strings
• supports falling back to rootDir: string as an argument for backwords compatibility
• upgrades commander to use variadic arguments to support rootDir from the cli

[smikula]

@Adjective-Object Is there a reason to prefer multiple root directories as opposed to adding an option to exclude directories? The latter seems more intuitive to me, and more in line with something like .gitignore or .prettierignore.

I'm imagining an optional ignoreDirs option (string[]) that — in order to be backward compatible — gets autopopulated with node_modules based on the ignoreExternalFences setting. Longer term supporting something like a .fencesignore file would be great.

[Adjective-Object]

Do you feel strongly about having an ignore file over a list of includes? As much as I like the aesthetics of .ignore files:

• There's no ecosystem coherence, Jest has a list of roots, prettier has an .ignorefile, tsconfig has both with the more commonly used in tutorials being "include"/
• Ignorefiles come with the expectation of git pattern matching, which means pulling in ignore, as well as supplying a way to set the ignore file from the command line.
• Ignorefiles also mean performing a directory tree traversal to find ignorefiles when not run in a repo root. Which means our FS walk has to to worry about symlink loops, and cross-fs boundaries.
• As you develop you are more likely to introduce more roots you want to ignore than roots you want to pay attention to (as is the case here). Moreover those new roots don't immediately cause failures, but rather cause slow performance degradation.

[smikula]

Looks like I don't have prettier configured in this repo yet. For my sanity, can you use single quotes for all the string literals in this file?

[Adjective-Object]

Looks like you beat me to it!