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, 15 insertions, 0 deletions

diff --git a/build/instructions.go b/build/instructions.go
index 1b954a2..38ea322 100644
--- a/build/instructions.go
+++ b/build/instructions.go
@@ -80,6 +80,14 @@ func (env Env) Compile() []string {
 	return defs
 }
 
+type Volume struct {
+	Path string
+}
+
+func (vol Volume) Compile() []string {
+	return []string{quote(vol.Path)}
+}
+
 func quote(arg string) string {
 	return strconv.Quote(arg)
 }
diff --git a/build/instructions_test.go b/build/instructions_test.go
index 8f9470c..04ebdfb 100644
--- a/build/instructions_test.go
+++ b/build/instructions_test.go
@@ -55,3 +55,9 @@ func TestEnv(t *testing.T) {
 		`quxname="quxvalue"`,
 	}, i.Compile())
 }
+
+func TestVolume(t *testing.T) {
+	i := build.Volume{"/foo/dir"}
+
+	assert.Equal(t, []string{`"/foo/dir"`}, i.Compile())
+}
diff --git a/build/phases.go b/build/phases.go
index 095263c..02e84e4 100644
--- a/build/phases.go
+++ b/build/phases.go
@@ -6,6 +6,7 @@ const (
 	PhasePrivileged Phase = iota
 	PhasePrivilegeDropped
 	PhasePreInstall
+	PhaseInstall
 	PhasePostInstall
 )