.gitignore exclusion is not working for a single file

The problem is simply because you are ignoring the directory dist. So Git will no longer look into the directory to look for other files.

As explained in this related answer, you need to whitelist the directory and only ignore its contents. Since you are having a nested structure, this does end up being a bit complicated though:

# ignore everything in the `dist` folder
dist/*
# … but don’t ignore the `dist/samples` folder
!dist/samples/
# … but ignore everything inside that `dist/samples` folder
dist/samples/*
# … except the `README.md` there
!dist/samples/README.md

This is also explicitly mentioned in the gitignore documentation (emphasis mine):

An optional prefix "!" which negates the pattern; any matching file excluded by a previous pattern will become included again. It is not possible to re-include a file if a parent directory of that file is excluded. Git doesn’t list excluded directories for performance reasons, so any patterns on contained files have no effect, no matter where they are defined.

I has the similar problem with another .gitignore in subdirectory. For examaple:

- root
-- Subdir
--- gulpfile.js
--- .gitignore
-- .gitignore

In root .gitignore where two rules:

*.js
!gulpfile.js

And in Subdir/gulpfile.js where another one rule:

*.js

Because of that, Subdir/gulpfile.js where ignored. To solve problem it is required to remove Subdir/.gitignore, or add !gulpfile.js to Subdir/.gitignore.

tl;dr:

/dist/**/*.*
!/dist/**/README.md
!/dist/samples/*.*

Proof it works:

tree dist -a
dist
├── bar
│   └── index.html
├── baz.js
├── foo
│   └── main.js
└── samples
    ├── README.md
    └── stuff.jpg

find dist -type f | git check-ignore --verbose --non-matching --stdin
.gitignore:1:/dist/**/*.*   dist/baz.js
.gitignore:2:!/dist/samples/*.* dist/samples/stuff.jpg
.gitignore:2:!/dist/samples/*.* dist/samples/README.md
.gitignore:1:/dist/**/*.*   dist/foo/main.js
.gitignore:1:/dist/**/*.*   dist/bar/index.html

---

Like https://stackoverflow.com/a/35279076/2496472 says, the docs mention:

An optional prefix "!" which negates the pattern; any matching file excluded by a previous pattern will become included again. It is not possible to re-include a file if a parent directory of that file is excluded. Git doesn’t list excluded directories for performance reasons, so any patterns on contained files have no effect, no matter where they are defined.

However, the docs also say:

Two consecutive asterisks ("**") in patterns matched against full pathname may have special meaning:

• A slash followed by two consecutive asterisks then a slash matches zero or more directories. For example, "a/**/b" matches "a/b", "a/x/b", "a/x/y/b" and so on.

Putting this together, the strategy is to never ignore a directory but ignore all files within a directory, and then exclude the file you want.

References:

• https://git-scm.com/docs/gitignore#_pattern_format
• https://git-scm.com/docs/git-check-ignore