Correctly handle empty directory when checking for missing file

[acordiner]

Description

The _is_file_missing() function uses a glob to determine if a file is missing. However, it has allow_empty = False, which
means an error will occur if an empty directory is searched.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature or functionality (non-breaking change which adds functionality)
• Style (white-space, formatting, etc...)
• Refactor (a code change that neither fixes a bug or adds a new feature)
• Performance (a code change that improves performance)
• Documentation (updates to documentation or READMEs)
• Chore (any other change that doesn't affect source or test files)

Properties of change

• Breaking change (this change will cause existing functionality to not work as expected)
• This change requires a documentation update

Test plan

How has this been tested?

• Covered by existing tests cases
• New test cases added
• Local testing

If part of the test plan included local testing, please provide instructions so we can reproduce. Please also list any relevant details for your test configuration.

Using write_source_file() with an empty directory results in the following erro:

Traceback (most recent call last):

File "/Users/alister/example/BUILD.bazel", line 22, column 17, in <toplevel>

example(

File "/Users/alister/example/rules.bzl", line 595, column 22, in example

write_source_file(

File "/private/var/tmp/_bazel_alister/fb38e376d8efddf3cdb91fd1e4a65c39/external/aspect_bazel_lib/lib/private/write_source_file.bzl", line 82, column 40, in 
write_source_file

out_file_missing = _is_file_missing(out_file)

File "/private/var/tmp/_bazel_alister/fb38e376d8efddf3cdb91fd1e4a65c39/external/aspect_bazel_lib/lib/private/write_source_file.bzl", line 374, column 28, in 
_is_file_missing

file_glob = native.glob([file_rel], exclude_directories = 0)

Error in glob: glob pattern 'empty_directory/foobar.txt' didn't match anything, but allow_empty is set to False (the default value of allow_empty can be set with 
--incompatible_disallow_empty_glob).

I believe the correct behaviour should be that _is_file_missing() returns false.

[alexeagle]

sounds correct to me, thanks!