Validate CD Step at Run instead of Validate (#519)

Summary:

Because TTPForge runs validations on TTP load, and we validate our target directory in the Validate action, the CD step will validate the existence of its target directory at TTP load.  This means that if you create your target directory as part of your TTP, your CD step will fail because the directory does not exist yet.

By moving the check to the run step, we will now hold off on validating the directory's existence until the CD step is run, allowing previous steps to create the target directory.

Reviewed By: inesusvet

Differential Revision: D65831540

example-ttps/actions/change-directory/runtime-created-directory.yaml

@@ -0,0 +1,28 @@
+---
+api_version: 2.0
+uuid: c15da914-de49-4297-a281-9c81b4fea413
+name: change_directory_example_with_runtime_created_directory
+description: |
+  This TTP shows you how to use the change_directory action type to change the
+  working directory for all future actions, even if the directory doesn't exist until
+  this TTP is ran.
+args:
+  - name: cd_destination
+    description: this argument is where we will try to cd to
+    default: /tmp/this_doesnt_exist_yet
+steps:
+  - name: "Initial directory"
+    inline: |
+      echo "Current working directory is: \"$(pwd)\""
+  - name: "Create directory"
+    inline: |
+      mkdir {{.Args.cd_destination}}
+    cleanup:
+      inline: |
+        rm -rf {{.Args.cd_destination}}
+  - name: "cd"
+    cd: {{.Args.cd_destination}}
+    cleanup: default
+  - name: "New directory"
+    inline: |
+      echo "Current working directory is: \"$(pwd)\""

pkg/blocks/changedirectory.go

@@ -63,21 +63,6 @@ func (step *ChangeDirectoryStep) Validate(_ TTPExecutionContext) error {
 		return err
 	}
 
-	// Check if cd is a valid directory
-	fsys := step.FileSystem
-	if fsys == nil {
-		fsys = afero.NewOsFs()
-	}
-
-	exists, err := afero.DirExists(fsys, step.Cd)
-	if err != nil {
-		return err
-	}
-
-	if !exists {
-		return fmt.Errorf("directory \"%s\" does not exist", step.Cd)
-	}
-
 	return nil
 }
 
@@ -96,6 +81,25 @@ func (step *ChangeDirectoryStep) Execute(ctx TTPExecutionContext) (*ActResult, e
 		step.Cd = step.PreviousCDStep.PreviousDir
 	}
 
+	// Check if cd is a valid directory
+	fsys := step.FileSystem
+	if fsys == nil {
+		if step.PreviousCDStep != nil && step.PreviousCDStep.FileSystem != nil {
+			fsys = step.PreviousCDStep.FileSystem
+		} else {
+			fsys = afero.NewOsFs()
+		}
+	}
+
+	exists, err := afero.DirExists(fsys, step.Cd)
+	if err != nil {
+		return nil, err
+	}
+
+	if !exists {
+		return nil, fmt.Errorf("directory \"%s\" does not exist", step.Cd)
+	}
+
 	logging.L().Infof("Changing directory to %s", step.Cd)
 
 	if step.Cd == "" {