Is it possible to copy files from a manifest or whitelist in a Dockerfile?

I know that docker supports a .dockerignore file to exclude files for COPY commands. What I am looking for is opposite: a way to whitelist or copy files from a manifest.

One can create such a manifest by running:

git ls-files > files-to-include.txt

Does the Dockerfile syntax support such feature? Or is there another way to get the same result?

There is no built-in way to do this. However, with a little hacking you can create an "inverse dockerignore file" like this:

include.sh

#!/usr/bin/env sh
FILE=.dockerignore
# add git indexed files
git ls-files > $FILE
# add NOT symbol in front of each line to keep
sed -i 's/^/!/' $FILE
# add * as the first line in the file
sed -i '1s/^/*\n&/' $FILE

.dockerignore

The result is something like this:

*
!.dockerignore
!.gitignore
!Dockerfile
!LICENSE
!README.md
!bin/action.sh
!bin/commitlint
!commitlint-plugin-tense/blacklist.txt
!commitlint-plugin-tense/index.js
!commitlint-plugin-tense/index.test.js
!commitlint-plugin-tense/package-lock.json
!commitlint-plugin-tense/package.json
!commitlint.config.js
!package.json
!yarn.lock

Conclusion

The first line * ignores all files. Each subsequent line in the prefixed with ! tells Docker to NOT ignore the given file. The result is essentially a whitelist of files to add using COPY directive in a Dockerfile. The main thing to watch out for is that this file can quickly become obsolete when adding or removing files and would have to be constantly maintained.