Smarter copies/sharedvolume/default behavior

Summary:
Defined new abstract `build.Volume` and corresponding
`docker.DockerVolume` instructions.

Refactored compilation of main `COPY` or `VOLUME` instruction for
application files to use the new instructions and moved injection of
these instructions out of the compiler and into `VariantConfig`. The
latter can be smarter about the following cases:

 1. When `copies` is set, simply depend on artifacts for the application
    files and do not copy anything from the build host.
 2. When `sharedvolume` is `true`, inject a `build.Volume` instruction
    for the application working directory.
 3. When neither of the above are set, copy application files from the
    host.

Fixes T174623
Depends on D768

Test Plan:
Run `go test ./...`. Run `blubber blubber.example.yaml production` and ensure:

 1. The `prep` stage has a `COPY . .` instruction.
 2. The final stage has no `COPY . .` instruction, only `COPY --from=prep`
    instructions.

Reviewers: thcipriani, mobrovac, hashar, mmodell, #release-engineering-team

Reviewed By: thcipriani, mobrovac, #release-engineering-team

Tags: #release-engineering-team

Maniphest Tasks: T174623

Differential Revision: https://phabricator.wikimedia.org/D769

3 files changed, 25 insertions, 5 deletions

diff --git a/docker/compiler.go b/docker/compiler.go
index 2891140..c9ca0fb 100644
--- a/docker/compiler.go
+++ b/docker/compiler.go
@@ -58,11 +58,7 @@ func CompileStage(buffer *bytes.Buffer, stage string, vcfg *config.VariantConfig
 
 	CompilePhase(buffer, vcfg, build.PhasePreInstall)
 
-	if vcfg.SharedVolume.True {
-		Writeln(buffer, "VOLUME [\"", vcfg.Runs.In, "\"]")
-	} else {
-		Writeln(buffer, "COPY . .")
-	}
+	CompilePhase(buffer, vcfg, build.PhaseInstall)
 
 	CompilePhase(buffer, vcfg, build.PhasePostInstall)
 
diff --git a/docker/instructions.go b/docker/instructions.go
index 2b00c1b..4edcb23 100644
--- a/docker/instructions.go
+++ b/docker/instructions.go
@@ -26,6 +26,10 @@ func NewDockerInstruction(instruction build.Instruction) (DockerInstruction, err
 		var dockerInstruction DockerEnv
 		dockerInstruction.arguments = instruction.Compile()
 		return dockerInstruction, nil
+	case build.Volume:
+		var dockerInstruction DockerVolume
+		dockerInstruction.arguments = instruction.Compile()
+		return dockerInstruction, nil
 	}
 
 	return nil, errors.New("Unable to create DockerInstruction")
@@ -77,6 +81,14 @@ func (de DockerEnv) Compile() string {
 		join(de.arguments, " "))
 }
 
+type DockerVolume struct{ abstractDockerInstruction }
+
+func (dv DockerVolume) Compile() string {
+	return fmt.Sprintf(
+		"VOLUME [%s]\n",
+		join(dv.arguments, ", "))
+}
+
 func join(arguments []string, delimiter string) string {
 	return removeNewlines(strings.Join(arguments, delimiter))
 }
diff --git a/docker/instructions_test.go b/docker/instructions_test.go
index fb9116b..10cc1ab 100644
--- a/docker/instructions_test.go
+++ b/docker/instructions_test.go
@@ -70,6 +70,18 @@ func TestEnv(t *testing.T) {
 	assert.Equal(t, "ENV bar=\"foo\" foo=\"bar\"\n", di.Compile())
 }
 
+func TestVolume(t *testing.T) {
+	i := build.Volume{"/foo/dir"}
+
+	di, err := docker.NewDockerInstruction(i)
+
+	var dockerVolume docker.DockerVolume
+
+	assert.Nil(t, err)
+	assert.IsType(t, dockerVolume, di)
+	assert.Equal(t, "VOLUME [\"/foo/dir\"]\n", di.Compile())
+}
+
 func TestEscapeRun(t *testing.T) {
 	i := build.Run{"/bin/true\nRUN echo HACKED!", []string{}}
 	dr, _ := docker.NewDockerInstruction(i)