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

4 files changed, 29 insertions, 1 deletions

diff --git a/config/lives.go b/config/lives.go
index 8d705e7..665a734 100644
--- a/config/lives.go
+++ b/config/lives.go
@@ -48,6 +48,10 @@ func (lives LivesConfig) InstructionsForPhase(phase build.Phase) []build.Instruc
 				build.Chown(lives.UID, lives.GID, LocalLibPrefix),
 			),
 		}}
+	case build.PhasePrivilegeDropped:
+		return []build.Instruction{
+			build.WorkingDirectory{lives.In},
+		}
 	}
 
 	return []build.Instruction{}
diff --git a/config/lives_test.go b/config/lives_test.go
index eeb91ef..dec1f99 100644
--- a/config/lives_test.go
+++ b/config/lives_test.go
@@ -73,7 +73,12 @@ func TestLivesConfigInstructions(t *testing.T) {
 	})
 
 	t.Run("PhasePrivilegeDropped", func(t *testing.T) {
-		assert.Empty(t, cfg.InstructionsForPhase(build.PhasePreInstall))
+		assert.Equal(t,
+			[]build.Instruction{
+				build.WorkingDirectory{"/some/directory"},
+			},
+			cfg.InstructionsForPhase(build.PhasePrivilegeDropped),
+		)
 	})
 
 	t.Run("PhasePreInstall", func(t *testing.T) {
diff --git a/config/variant.go b/config/variant.go
index 0cb3f09..e3562bf 100644
--- a/config/variant.go
+++ b/config/variant.go
@@ -68,6 +68,10 @@ func (vc *VariantConfig) InstructionsForPhase(phase build.Phase) []build.Instruc
 	case build.PhasePostInstall:
 		switchUser = vc.Runs.As
 		instructions = build.ApplyUser(vc.Runs.UID, vc.Runs.GID, instructions)
+
+		if len(vc.EntryPoint) > 0 {
+			instructions = append(instructions, build.EntryPoint{vc.EntryPoint})
+		}
 	}
 
 	if switchUser != "" {
diff --git a/config/variant_test.go b/config/variant_test.go
index 6890f6d..f906e67 100644
--- a/config/variant_test.go
+++ b/config/variant_test.go
@@ -135,6 +135,21 @@ func TestVariantConfigInstructions(t *testing.T) {
 				cfg.InstructionsForPhase(build.PhasePostInstall),
 			)
 		})
+
+		t.Run("with entrypoint", func(t *testing.T) {
+			cfg := config.VariantConfig{
+				CommonConfig: config.CommonConfig{
+					EntryPoint: []string{"/foo", "bar"},
+				},
+			}
+
+			assert.Equal(t,
+				[]build.Instruction{
+					build.EntryPoint{[]string{"/foo", "bar"}},
+				},
+				cfg.InstructionsForPhase(build.PhasePostInstall),
+			)
+		})
 	})
 }