Allow Dockerfile from outside build-context

[thaJeztah]

Historically, the Dockerfile had to be insde the build-context, because it was sent as part of the build-context.

moby/moby@3f6dc81 added support for passing the Dockerfile through stdin, in which case the contents of the Dockerfile is injected into the build-context.

This patch uses the same mechanism for situations where the location of the Dockerfile is passed, and its path is outside of the build-context.

Before this change:

$ mkdir -p myproject/context myproject/dockerfiles && cd myproject
$ echo "hello" > context/hello
$ echo -e "FROM busybox\nCOPY /hello /\nRUN cat /hello" > dockerfiles/Dockerfile
$ docker build --no-cache -f $PWD/dockerfiles/Dockerfile $PWD/context

unable to prepare context: the Dockerfile (/Users/sebastiaan/projects/test/dockerfile-outside/myproject/dockerfiles/Dockerfile) must be within the build context

After this change:

$ mkdir -p myproject/context myproject/dockerfiles && cd myproject
$ echo "hello" > context/hello
$ echo -e "FROM busybox\nCOPY /hello /\nRUN cat /hello" > dockerfiles/Dockerfile
$ docker build --no-cache -f $PWD/dockerfiles/Dockerfile $PWD/context

Sending build context to Docker daemon  2.607kB
Step 1/3 : FROM busybox
 ---> 6ad733544a63
Step 2/3 : COPY /hello /
 ---> 9a5ae1c7be9e
Step 3/3 : RUN cat /hello
 ---> Running in 20dfef2d180f
hello
Removing intermediate container 20dfef2d180f
 ---> ce1748f91bb2
Successfully built ce1748f91bb2

- What I did

Added support for building from a Dockerfile that's outside the build-context

- How I did it

See above

- How to verify it

See above

- Description for the changelog

+ Allow Dockerfile to be outside of build-context [docker/cli#886](https://github.com/docker/cli/pull/886)

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

Opening as WIP because tests still have to be updated/added

[codecov-io]

Codecov Report

Merging #886 into master will decrease coverage by 0.46%.
The diff coverage is 42.85%.

@@            Coverage Diff             @@
##           master     #886      +/-   ##
==========================================
- Coverage    53.2%   52.73%   -0.47%     
==========================================
  Files         258      257       -1     
  Lines       16338    16409      +71     
==========================================
- Hits         8692     8653      -39     
- Misses       7081     7185     +104     
- Partials      565      571       +6

[vdemeester]

Desgin SGTM

[thaJeztah]

Added a unit-test. Was also considering updating the e2e test TestBuildFromContextDirectoryWithTag(), but wasn't sure if we would be comfortable updating that test, or adding a second one;

diff --git a/e2e/image/build_test.go b/e2e/image/build_test.go
index b94566d3..61dee27f 100644
--- a/e2e/image/build_test.go
+++ b/e2e/image/build_test.go
@@ -15,16 +15,21 @@ func TestBuildFromContextDirectoryWithTag(t *testing.T) {
        dir := fs.NewDir(t, "test-build-context-dir",
                fs.WithFile("run", "echo running", fs.WithMode(0755)),
                fs.WithDir("data", fs.WithFile("one", "1111")),
-               fs.WithFile("Dockerfile", fmt.Sprintf(`
+       )
+       defer dir.Remove()
+
+       // Dockerfile outside of build-context
+       dockerFile := fs.NewFile(t, "test-build-dockerfile-dir",
+               fs.WithContent(fmt.Sprintf(`
        FROM    %s
        COPY    run /usr/bin/run
        RUN             run
        COPY    data /data
                `, fixtures.AlpineImage)))
-       defer dir.Remove()
+       defer dockerFile.Remove()
 
        result := icmd.RunCmd(
-               icmd.Command("docker", "build", "-t", "myimage", "."),
+               icmd.Command("docker", "build", "-t", "myimage", "-f", dockerFile.Path(), "."),
                withWorkingDir(dir))
 
        result.Assert(t, icmd.Expected{Err: icmd.None})

[dnephin]

LGTM

I don't think we need another e2e test here, the unit test covers it.

[vdemeester]

LGTM 🐯
cc @tonistiigi