How to use .gitgnore for Dockerfile because .dockerignore sucks

.README.md

Want to exclude patterns of files at any folder depth?

Pulling your hair out because .dockerignore (Go filepath.Match) sucks?

Don't waste time with .dockerignore

Make use of tar's pattern matching together with Docker's tar support and save your sanity!

docker-build.sh

# docker-build.sh
#!/bin/bash

# Where code is the folder containing your code
tar --exclude-from=.gitignore -C code -cvf docker.tar .
docker build -t my-image .

Dockerfile

FROM baseimage
# Docker automagically extracts tars using the ADD instruction
ADD docker.tar .