DIGGER_PLANFILE in apply runs (#2087)

* DIGGER_PLANFILE in apply runs

Author: motatoes

docs/ce/howto/custom-commands.mdx

@@ -45,7 +45,6 @@ You can add extra arguments to the plan command by setting the `extra_args` key
 However in some cases if you wish to override the plan command entirely you can do it by excluding the plan in the steps and having your command specified in the run like so:
 
 ```
-
 workflows:
   default:
     plan:
@@ -55,4 +54,21 @@ workflows:
         - run: terraform plan -input=false -refresh -no-color -out $DIGGER_PLANFILE
 ```
 
-Note that you need to use the -out flag to write the output to the $DIGGER_PLANFILE env variable, since this will be used in postprocessing steps by digger.
+Note that you need to use the -out flag to write the output to the $DIGGER_PLANFILE env variable, since this will be used in postprocessing steps by digger.
+
+Similarly for the apply step you can use the $DIGGER_PLANFILE env variable to point to the plan file to apply. Note that this will only work when you have the [plan persistence](/ce/howto/store-plans-in-a-bucket)
+configured. If plan persistence is not configured, the $DIGGER_PLANFILE environment variable will not be set during the apply step. Here is an example with both plan and apply commands overriden:
+
+```
+workflows:
+  default:
+    plan:
+      steps:
+        - init
+        - run: terraform plan -input=false -refresh -no-color -out $DIGGER_PLANFILE
+    apply:
+      steps:
+        - init
+        - run: terraform apply -input=false -no-color $DIGGER_PLANFILE
+
+```

libs/execution/execution.go

@@ -224,6 +224,11 @@ func (d DiggerExecutor) Plan() (*iac_utils.IacSummary, bool, bool, string, strin
 		return step.Action == "plan"
 	})
 
+	// setting additional env vars for run step
+	if d.RunEnvVars == nil {
+		d.RunEnvVars = make(map[string]string)
+	}
+
 	for _, step := range planSteps {
 		slog.Info("Running step", "action", step.Action)
 		if step.Action == "init" {
@@ -266,10 +271,7 @@ func (d DiggerExecutor) Plan() (*iac_utils.IacSummary, bool, bool, string, strin
 			slog.Info("Running command",
 				"command", step.Value,
 				"project", d.ProjectNamespace+"#"+d.ProjectName)
-			// setting additional env vars for run step
-			if d.RunEnvVars == nil {
-				d.RunEnvVars = make(map[string]string)
-			}
+
 			slog.Debug("adding plan file path to environment", "DIGGER_PLANFILE", d.PlanPathProvider.LocalPlanFilePath())
 			d.RunEnvVars["DIGGER_PLANFILE"] = d.PlanPathProvider.LocalPlanFilePath()
 			_, _, err := d.CommandRunner.Run(d.ProjectPath, step.Shell, commands, d.RunEnvVars)
@@ -382,6 +384,11 @@ func (d DiggerExecutor) Apply() (*iac_utils.IacSummary, bool, string, error) {
 		}
 	}
 
+	if d.RunEnvVars == nil {
+		slog.Debug("RunEnvVars is nil, creating new map")
+		d.RunEnvVars = make(map[string]string)
+	}
+
 	for _, step := range applySteps {
 		if step.Action == "init" {
 			stdout, stderr, err := d.TerraformExecutor.Init(step.ExtraArgs, d.StateEnvVars)
@@ -411,6 +418,11 @@ func (d DiggerExecutor) Apply() (*iac_utils.IacSummary, bool, string, error) {
 			if os.Getenv("ACTIVATE_VENV") == "true" {
 				commands = append(commands, fmt.Sprintf("source %v/.venv/bin/activate", os.Getenv("GITHUB_WORKSPACE")))
 			}
+
+			if plansFilename != nil {
+				slog.Debug("adding plan file path to environment", "DIGGER_PLANFILE", *plansFilename)
+				d.RunEnvVars["DIGGER_PLANFILE"] = *plansFilename
+			}
 			commands = append(commands, step.Value)
 			slog.Info("Running command",
 				"command", step.Value,