Source files are copied onto themselves when running `grunt watch --dev` (`npm run dev`)

[westonruter]

In the wordpress-develop repo, I have a plugin file located in src/wp-content/plugins/. I've also initiated npm run dev (grunt watch --dev). I noticed in PhpStorm when editing the plugin file that often the editor complains about the file being modified on disk and whether I want to reload the file or use the copy in memory. What I think is happening is that the editor is I'll make a change and save and then I'll make another change and save again after a couple seconds. After the first save, the watch command picks up on the change to the file and it is copying the file onto itself and thus bumping the modified time, causing the editor to detect a conflict at the second save. It turns out that this is not only the case for files in src/wp-content/plugins but all source files. It seems that grunt watch is erroneously copying source files onto itself when using the --dev option.

[westonruter]

Screenshot of PhpStorm showing issue

Trac ticket: https://core.trac.wordpress.org/ticket/59196

[westonruter]

In 56461:

Build Tools: Avoid doing copy:dynamic when running grunt watch when using --dev option.

This prevents erroneously copying a file from source onto itself in source.

Props westonruter, jorbin.
Fixes #59196.

Committed in r56461

[westonruter]

Reopening for 6.3.2 consideration.

[audrasjb]

In 56782:

Build Tools: Avoid doing copy:dynamic when running grunt watch when using --dev option.

This prevents erroneously copying a file from source onto itself in source.

Props westonruter, jorbin.
Merges [56461] to the 6.3 branch.
Fixes #59196.