Display informative message when arc launches an editor

Summary:
Update `PhutilInteractiveEditor` to allow specifying a "task message" which will be displayed just prior to launching the user's editor.

Refs T3271

Test Plan: I ran several `arc diff` commands in varying states to invoke my editor and verified that it printed out the text indicating that my editor was being launched.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Maniphest Tasks: T3271

Differential Revision: https://secure.phabricator.com/D21700

src/console/PhutilInteractiveEditor.php

@@ -22,6 +22,7 @@ final class PhutilInteractiveEditor extends Phobject {
   private $offset   = 0;
   private $preferred;
   private $fallback;
+  private $taskMessage;
 
 
 /* -(  Creating a New Editor  )---------------------------------------------- */
@@ -74,6 +75,20 @@ final class PhutilInteractiveEditor extends Phobject {
     $editor = $this->getEditor();
     $offset = $this->getLineOffset();
 
+    $binary = basename($editor);
+
+    // This message is primarily an assistance to users with GUI-based
+    // editors configured. Users with terminal-based editors won't have a
+    // chance to see this prior to the editor being launched.
+    echo tsprintf(
+      "%s\n",
+      pht('Launching editor "%s"...', $binary));
+
+    $task_message = $this->getTaskMessage();
+    if ($task_message !== null) {
+      echo tsprintf("%s\n", $task_message);
+    }
+
     $err = $this->invokeEditor($editor, $path, $offset);
 
     if ($err) {
@@ -85,7 +100,6 @@ final class PhutilInteractiveEditor extends Phobject {
         'vim' => true,
       );
 
-      $binary = basename($editor);
       if (isset($vi_binaries[$binary])) {
         // This runs "Q" (an invalid command), then "q" (a valid command,
         // meaning "quit"). Vim binaries with behavior that makes them poor
@@ -266,6 +280,33 @@ final class PhutilInteractiveEditor extends Phobject {
     return $this;
   }
 
+  /**
+   * Set the message that identifies the task for which the editor is being
+   * launched, displayed to the user prior to it being launched.
+   *
+   * @param  string  The message to display to the user.
+   * @return $this
+   *
+   * @task config
+   */
+  public function setTaskMessage($task_message) {
+    $this->taskMessage = $task_message;
+    return $this;
+  }
+
+  /**
+   * Retrieve the current message that will display to the user just prior to
+   * invoking the editor.
+   *
+   * @return string  The message that will display to the user, or null if no
+   *   message will be displayed.
+   *
+   * @task config
+   */
+  public function getTaskMessage() {
+    return $this->taskMessage;
+  }
+
 
   /**
    * Get the name of the editor program to use. The value of the environmental

src/workflow/ArcanistDiffWorkflow.php

@@ -674,6 +674,8 @@ EOTEXT
       if ($should_edit) {
         $edited = $this->newInteractiveEditor($remote_corpus)
           ->setName('differential-edit-revision-info')
+          ->setTaskMessage(pht(
+            'Update the details for a revision, then save and exit.'))
           ->editInteractively();
         if ($edited != $remote_corpus) {
           $remote_corpus = $edited;
@@ -1476,6 +1478,8 @@ EOTEXT
       } else {
         $new_template = $this->newInteractiveEditor($template)
           ->setName('new-commit')
+          ->setTaskMessage(pht(
+            'Provide the details for a new revision, then save and exit.'))
           ->editInteractively();
       }
       $first = false;
@@ -1752,6 +1756,8 @@ EOTEXT
 
     $comments = $this->newInteractiveEditor($template)
       ->setName('differential-update-comments')
+      ->setTaskMessage(pht(
+        'Update the revision comments, then save and exit.'))
       ->editInteractively();
 
     return $comments;

src/workflow/ArcanistPatchWorkflow.php

@@ -909,6 +909,8 @@ EOTEXT
 
       $commit_message = $this->newInteractiveEditor($template)
         ->setName('arcanist-patch-commit-message')
+        ->setTaskMessage(pht(
+          'Supply a commit message for this patch, then save and exit.'))
         ->editInteractively();
 
       $commit_message = ArcanistCommentRemover::removeComments($commit_message);

src/workflow/ArcanistWorkflow.php

@@ -1234,6 +1234,9 @@ abstract class ArcanistWorkflow extends Phobject {
 
         $commit_message = $this->newInteractiveEditor($template)
           ->setName(pht('commit-message'))
+          ->setTaskMessage(pht(
+            'Supply commit message for uncommitted changes, then save and '.
+            'exit.'))
           ->editInteractively();
 
         if ($commit_message === $template) {