`make docker` fails when the repo is cloned as a submodule

[scjudd]

If the repo is cloned as a submodule, make docker fails. This is due to the fact that GITCOMMIT_SHA doesn't exist before make runs within the build container, and the true .git/ directory is outside of the Docker build context when we're in a submodule.

I was able to fix this by making GITCOMMIT_SHA a dependency of the docker make target in the Makefile, such that GITCOMMIT_SHA already exists in the Docker build context before make runs. I have opened #185 with the fix.

Example

~$ EXAMPLE_DIR=$(mktemp -d)

~$ cd $EXAMPLE_DIR

tmp.MEpbWK5rCB$ git init
Initialized empty Git repository in /tmp/tmp.MEpbWK5rCB/.git/

tmp.MEpbWK5rCB$ git submodule add git@github.com:awslabs/amazon-ecr-credential-helper.git
Cloning into '/tmp/tmp.MEpbWK5rCB/amazon-ecr-credential-helper'...
remote: Enumerating objects: 373, done.
remote: Counting objects: 100% (373/373), done.
remote: Compressing objects: 100% (300/300), done.
remote: Total 2186 (delta 90), reused 205 (delta 55), pack-reused 1813
Receiving objects: 100% (2186/2186), 2.60 MiB | 11.09 MiB/s, done.
Resolving deltas: 100% (889/889), done.

tmp.MEpbWK5rCB$ cd amazon-ecr-credential-helper/

amazon-ecr-credential-helper$ make docker
find: ‘.git/’: Not a directory
mkdir -p bin
docker run --rm \
-e TARGET_GOOS= \
-e TARGET_GOARCH= \
-v '/tmp/tmp.MEpbWK5rCB/amazon-ecr-credential-helper/bin':/go/src/github.com/awslabs/amazon-ecr-credential-helper/bin \
sha256:dfe7b32b42631a793e59eb8c18b99da8df91fa3717ecc4fa4d0323a1ccf84110
find: '.git/': Not a directory
git rev-parse --short=7 HEAD > GITCOMMIT_SHA
fatal: Not a git repository: ../.git/modules/amazon-ecr-credential-helper
make: *** [GITCOMMIT_SHA] Error 128
Makefile:75: recipe for target 'GITCOMMIT_SHA' failed
Makefile:32: recipe for target 'docker' failed
make: *** [docker] Error 2

[samuelkarp]

Hi @scjudd! I'm really curious to know more about why you're attempting to build the credential helper inside a submodule. If you're not already aware, there are prebuilt binaries and source releases that don't require git.

[scjudd]

I actually would happily use the prebuilt binaries if I could checkout version 0.3.1, run make docker and produce the same SHA256 hash as the pre-built binaries. It seemed this was an easier ask than deterministic builds.

[samuelkarp]

Thanks! I've opened #186 to track reproducible builds, since this is something I've wanted anyway.

For your use-case of building yourself, another alternative is to build from a source tarball that already contains a rendered GITCOMMIT_SHA file; this tarball does not depend on having a working git checkout.

[samuelkarp]

I've merged #185 to address this. #186 will continue to track reproducible builds.