Prepend plan steps with filepath env (#721)

Supports this env var within the plan step of the terraform workflow as
requested. Should not require versioning as usage of variable happens
within an activity.

server/neptune/gateway/deploy/signaler.go

@@ -18,6 +18,8 @@ type signaler interface {
 const (
 	Deprecated = "deprecated"
 	Destroy    = "-destroy"
+	Manifest   = "manifest_path"
+	EnvStep    = "env"
 )
 
 type WorkflowSignaler struct {
@@ -52,7 +54,7 @@ func (d *WorkflowSignaler) SignalWithStartWorkflow(ctx context.Context, rootCfg
 			Root: workflows.Root{
 				Name: rootCfg.Name,
 				Plan: workflows.Job{
-					Steps: d.generateSteps(rootCfg.DeploymentWorkflow.Plan.Steps),
+					Steps: d.prependPlanEnvSteps(rootCfg),
 				},
 				Apply: workflows.Job{
 					Steps: d.generateSteps(rootCfg.DeploymentWorkflow.Apply.Steps),
@@ -94,6 +96,20 @@ func BuildDeployWorkflowID(repoName string, rootName string) string {
 	return fmt.Sprintf("%s||%s", repoName, rootName)
 }
 
+func (d *WorkflowSignaler) prependPlanEnvSteps(cfg *valid.MergedProjectCfg) []workflows.Step {
+	var steps []workflows.Step
+	if t, ok := cfg.Tags[Manifest]; ok {
+		//this is a Lyft specific env var
+		steps = append(steps, workflows.Step{
+			StepName:    EnvStep,
+			EnvVarName:  "MANIFEST_FILEPATH",
+			EnvVarValue: t,
+		})
+	}
+	steps = append(steps, d.generateSteps(cfg.DeploymentWorkflow.Plan.Steps)...)
+	return steps
+}
+
 func (d *WorkflowSignaler) generateSteps(steps []valid.Step) []workflows.Step {
 	// NOTE: for deployment workflows, we won't support command level user requests for log level output verbosity
 	var workflowSteps []workflows.Step

server/neptune/gateway/pr/signaler.go

@@ -145,13 +145,27 @@ func (s *WorkflowSignaler) buildRoots(rootCfgs []*valid.MergedProjectCfg, valida
 			RepoRelPath: rootCfg.RepoRelDir,
 			TfVersion:   tfVersion,
 			PlanMode:    generatePlanMode(rootCfg),
-			Plan:        workflows.PRJob{Steps: generateSteps(rootCfg.PullRequestWorkflow.Plan.Steps)},
+			Plan:        workflows.PRJob{Steps: s.prependPlanEnvSteps(rootCfg)},
 			Validate:    workflows.PRJob{Steps: s.prependValidateEnvSteps(rootCfg, validateEnvOpts...)},
 		})
 	}
 	return roots
 }
 
+func (s *WorkflowSignaler) prependPlanEnvSteps(cfg *valid.MergedProjectCfg) []workflows.PRStep {
+	var steps []workflows.PRStep
+	if t, ok := cfg.Tags[Manifest]; ok {
+		//this is a Lyft specific env var
+		steps = append(steps, workflows.PRStep{
+			StepName:    EnvStep,
+			EnvVarName:  "MANIFEST_FILEPATH",
+			EnvVarValue: t,
+		})
+	}
+	steps = append(steps, generateSteps(cfg.PullRequestWorkflow.Plan.Steps)...)
+	return steps
+}
+
 func (s *WorkflowSignaler) prependValidateEnvSteps(rootCfg *valid.MergedProjectCfg, opts ...ValidateEnvs) []workflows.PRStep {
 	for _, o := range opts {
 		initialEnvSteps := s.generatePRModeEnvSteps(rootCfg, o)