COPY ./.git X command errors in buildx v0.13.1

[dhedey]

Summary

Until a recent upgrade, a command such as COPY ./.git /build-dir/.git was working fine. It's perhaps a little questionable copying a git folder into a docker image, but we were using it for builds, and our build script reads tag information from the git directory - so it's certainly defensible.

Now it errors with:

ERROR: failed to solve: source can't be a git ref for COPY
Error: buildx failed with: ERROR: failed to solve: source can't be a git ref for COPY

Using

/usr/bin/docker buildx version
  github.com/docker/buildx v0.13.1 788433953af10f2a698f5c07611dddce2e08c7a0

Likely cause

I believe this relates to #4142 - although I'm not sure why we've only just seen the issue now. Maybe it's taken a while for the release to hit our CI server, or maybe there's some other more recent update which has triggered this code path.

Specifically:

• This line 70 sees ./.git converted to https://./.git
• This line 84/85 sees https://./.git be interpreted as a valid git reference.

I think the fallback assumption that a path is https:// is too excessive. Basically any path ending .git would hit this issue.

As a workaround in our case, we might be able to do something like this: COPY ./.git/* /build-dir/.git/ but I still need to test this (cf moby/moby#15771)

[tonistiigi]

#4776

[raylu]

I don't think the above fixes it in general. we have a build context with an absolute path (/src.git)
so when we build

$ cat Dockerfile 
FROM alpine

COPY --from=src file /

this still breaks. it used to work in docker 24.0.5:

$ docker buildx version
github.com/docker/buildx v0.11.2 9872040b6626fb7d87ef7296fd5b832e8cc2ad17

but in docker 24.0.9 and 25.0.3,

 $ docker buildx version
github.com/docker/buildx v0.13.1 788433953af10f2a698f5c07611dddce2e08c7a0
~ $ docker buildx build --build-context src=/src.git .
[+] Building 0.2s (4/4) FINISHED                                                                                   docker:default
 => [internal] load local bake definitions                                                                                   0.0s
 => => reading Bakefile 246B / 246B                                                                                          0.0s
 => [internal] load build definition from Dockerfile                                                                         0.0s
 => => transferring dockerfile: 73B                                                                                          0.0s
 => [internal] load .dockerignore                                                                                            0.0s
 => => transferring context: 2B                                                                                              0.0s
 => CANCELED [internal] load metadata for docker.io/library/alpine:latest                                                    0.0s
Dockerfile:3
--------------------
   1 |     FROM alpine
   2 |     
   3 | >>> COPY --from=src file /
   4 |     
--------------------
ERROR: failed to solve: invalid context specifier /src.git for src

the fix in eb41916 only works if the path starts with ./ or ../, which our absolute paths don't