Generalize instructions for entrypoint and working directory

Summary:
Introduce new `build.EntryPoint` and `build.WorkingDirectory`
instructions to allow configuration to inject them instead of hard
coding their generation in the Docker compiler.

Simplified the Docker compiler to simply iterate over build phases as
returned by a new function `build.Phases()`.

Depends on D990

Test Plan: Run `go test ./...`.

Reviewers: thcipriani, demon, hashar, #release-engineering-team

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D991

3 files changed, 49 insertions, 0 deletions

diff --git a/build/instructions.go b/build/instructions.go
index 91caa6b..295221e 100644
--- a/build/instructions.go
+++ b/build/instructions.go
@@ -109,6 +109,18 @@ func (cf CopyFrom) Compile() []string {
 	return append([]string{cf.From}, cf.Copy.Compile()...)
 }
 
+// EntryPoint is a build instruction for declaring a container's default
+// runtime process.
+type EntryPoint struct {
+	Command []string // command and arguments
+}
+
+// Compile returns the quoted entrypoint command and arguments.
+//
+func (ep EntryPoint) Compile() []string {
+	return quoteAll(ep.Command)
+}
+
 // Env is a concrete build instruction for declaring a container's runtime
 // environment variables.
 //
@@ -163,6 +175,19 @@ func (vol Volume) Compile() []string {
 	return []string{quote(vol.Path)}
 }
 
+// WorkingDirectory is a build instruction for defining the working directory
+// for future command and entrypoint instructions.
+//
+type WorkingDirectory struct {
+	Path string // working directory path
+}
+
+// Compile returns the quoted working directory path.
+//
+func (wd WorkingDirectory) Compile() []string {
+	return []string{quote(wd.Path)}
+}
+
 func compileSortedKeyValues(keyValues map[string]string) []string {
 	defs := make([]string, 0, len(keyValues))
 	names := make([]string, 0, len(keyValues))
diff --git a/build/instructions_test.go b/build/instructions_test.go
index f6e3628..29508e2 100644
--- a/build/instructions_test.go
+++ b/build/instructions_test.go
@@ -48,6 +48,12 @@ func TestCopyFrom(t *testing.T) {
 	assert.Equal(t, []string{"foo", `"source1"`, `"source2"`, `"dest"`}, i.Compile())
 }
 
+func TestEntryPoint(t *testing.T) {
+	i := build.EntryPoint{[]string{"/bin/foo", "bar", "baz"}}
+
+	assert.Equal(t, []string{`"/bin/foo"`, `"bar"`, `"baz"`}, i.Compile())
+}
+
 func TestEnv(t *testing.T) {
 	i := build.Env{map[string]string{
 		"fooname": "foovalue",
@@ -87,3 +93,9 @@ func TestVolume(t *testing.T) {
 
 	assert.Equal(t, []string{`"/foo/dir"`}, i.Compile())
 }
+
+func TestWorkingDirectory(t *testing.T) {
+	i := build.WorkingDirectory{"/foo/path"}
+
+	assert.Equal(t, []string{`"/foo/path"`}, i.Compile())
+}
diff --git a/build/phases.go b/build/phases.go
index 3480927..a656727 100644
--- a/build/phases.go
+++ b/build/phases.go
@@ -22,3 +22,15 @@ const (
 type PhaseCompileable interface {
 	InstructionsForPhase(phase Phase) []Instruction
 }
+
+// Phases returns all build phases in the order to be compiled.
+//
+func Phases() []Phase {
+	return []Phase{
+		PhasePrivileged,
+		PhasePrivilegeDropped,
+		PhasePreInstall,
+		PhaseInstall,
+		PhasePostInstall,
+	}
+}