Add module that creates a permanent revision from a significantly modified autosave

bin/phpcs-whitelist.js

@@ -12,6 +12,7 @@ module.exports = [
 	'_inc/lib/class.jetpack-password-checker.php',
 	'_inc/lib/admin-pages/class-jetpack-about-page.php',
 	'load-jetpack.php',
+	'modules/autosave-revisions.php',
 	'modules/masterbar/',
 	'modules/memberships/',
 	'modules/module-extras.php',

modules/autosave-revisions.php

@@ -0,0 +1,137 @@
+<?php
+/**
+ * Autosave Revisions
+ * More reliable autosaves that save a permanent revision before large changes
+ */
+
+/**
+ * Compare the proposed update with the last stored revision verifying that
+ * they are different, unless a plugin tells us to always save regardless.
+ *
+ * TODO: this function is extracted from Core's wp_save_post_revision function. Submit it as
+ *       a Core patch and then use it here after it's merged.
+ *
+ * @param int $post_id The ID of the post to save as a revision.
+ * @param WP_Post $post The proposed post update.
+ * @return bool Whether the proposed update is different from the last saved revision.
+ */
+function jetpack_post_has_changed_since_last_revision( $post_id, $post ) {
+	$revisions = wp_get_post_revisions( $post_id );
+	// If no previous revisions, save one
+	if ( ! $revisions ) {
+		return true;
+	}
+
+	// grab the last revision, but not an autosave
+	foreach ( $revisions as $revision ) {
+		if ( false !== strpos( $revision->post_name, "{$revision->post_parent}-revision" ) ) {
+			$last_revision = $revision;
+			break;
+		}
+	}
+
+	if ( ! isset( $last_revision ) ) {
+		return true;
+	}
+
+	if ( ! apply_filters( 'wp_save_post_revision_check_for_changes', $check_for_changes = true, $last_revision, $post ) ) {
+		return true;
+	}
+
+	$post_has_changed = false;
+
+	foreach ( array_keys( _wp_post_revision_fields( $post ) ) as $field ) {
+		if ( normalize_whitespace( $post->$field ) != normalize_whitespace( $last_revision->$field ) ) {
+			$post_has_changed = true;
+			break;
+		}
+	}
+
+	$post_has_changed = (bool) apply_filters( 'wp_save_post_revision_post_has_changed', $post_has_changed, $last_revision, $post );
+
+	return $post_has_changed;
+}
+
+/**
+ * Determine if the two versions (autosave revisions) of a post are different enough to warrant
+ * saving the old autosave as a separate post revision.
+ */
+function jetpack_is_big_edit( $post_before, $post_after ) {
+	// TODO: make the criteria more reasonable, maybe even make a text diff and look at its +-.
+	$before_len = strlen( $post_before->post_content );
+	$after_len = strlen( $post_after->post_content );
+	$size_diff = absint( $after_len - $before_len );
+	// depends on size: starts at 50 chars (approx one line) for smallest posts, and ends up
+	// being at least 250 chars for 1000 chars posts and bigger.
+	$size_threshold = 50 + min( $before_len, 1000 ) / 5;
+	return $size_diff > $size_threshold;
+}
+
+/**
+ * When a post is autosaved, we don't create a post revision for that save. On multiple
+ * consecutive autosaves, we overwrite the old autosave (i.e., the post itself in case of drafts or
+ * an autosave revision in case of published posts) and its content is lost forever.
+ *
+ * This function will compare the old and new autosave, determine if they are significantly
+ * from each other and if they are, saves the old autosave as a separate post revision.
+ * This prevents losing valuable unsaved content in case an autosave goes awry, e.g., it empties
+ * the post content due to an editor bug or unwanted edit.
+ */
+function jetpack_create_autosave_revision( $post_ID, $post_after, $post_before ) {
+	// we are only interested in post changes done during autosave
+	if ( ! defined( 'DOING_AUTOSAVE' ) || ! DOING_AUTOSAVE ) {
+		return;
+	}
+
+	// get the actual post whose revision is to be saved: we might need to reach out for the parent
+	// post if the update is for autosave revision. It's simply the $post_before for draft autosave.
+	$revision_post = $post_before;
+
+	if ( $post_before->post_type === 'revision' ) {
+		if ( strpos( $post_before->post_name, "{$post_before->post_parent}-autosave" ) === false ) {
+			// update of a non-autosave revision: we're not interested in this kind of update
+			return;
+		}
+
+		// it's an update of autosave revision, retrieve the parent post
+		$revision_post = get_post( $post_before->post_parent );
+	}
+
+	// bail out if the post type doesn't support revisions
+	if ( ! wp_revisions_enabled( $revision_post ) ) {
+		return;
+	}
+
+	// the autosave revision can either have fresh content, if it's newer than the saved post, or
+	// be stale: we don't delete the autosave revision when saving the post. We'll reuse it later
+	// on the next autosave instead of creating a new one.
+	// If the autosave is indeed fresh, update the parent post with its content and timestamp before
+	// saving it as revision.
+	if ( $post_before->post_modified > $revision_post->post_modified) {
+		foreach ( array_keys( _wp_post_revision_fields( $revision_post ) ) as $field ) {
+			$revision_post->$field = $post_before->$field;
+		}
+		$revision_post->post_modified = $post_before->post_modified;
+		$revision_post->post_modified_gmt = $post_before->post_modified_gmt;
+	}
+
+	// don't save a revision if it would be identical to the last saved revision
+	if ( ! jetpack_post_has_changed_since_last_revision( $revision_post->ID, $revision_post ) ) {
+		return;
+	}
+
+	// we'll save a post revision only if the difference between the old and new autosave is big.
+	// then the old autosave is worth preserving: it would be overwritten and lost otherwise.
+	if ( ! jetpack_is_big_edit( $revision_post, $post_after ) ) {
+		return;
+	}
+
+	_wp_put_post_revision( $revision_post );
+
+	// record stats about count and size of created autosave revisions
+	$revision_content_length = strlen( $revision_post->post_content );
+	do_action( 'jetpack_stats_statsd', 'autosave_revision', "1|c" );
+	do_action( 'jetpack_stats_statsd', 'autosave_revision', "{$revision_content_length}|g" );
+}
+
+add_action( 'post_updated', 'jetpack_create_autosave_revision', 10, 3 );

modules/module-extras.php

@@ -13,6 +13,7 @@
  *    - When connected to WordPress.com.
  */
 $tools = array(
+	'autosave-revisions.php',
 	// Always loaded, but only registered if theme supports it.
 	'custom-post-types/comics.php',
 	'custom-post-types/testimonial.php',

to-test.md

@@ -1,3 +1,15 @@
+## 7.7
+
+### Autosave Revisions
+
+This feature introduces more reliable autosaves that save a permanent revision whenever a large (measured by post content length) change is autosave that would overwrite the previous autosave.
+
+**Testing instructions:**
+1. edit a draft or published post in various editors (Classic or Block)
+2. add one character and wait for autosave. Check that permanent revision was not created. (best done with revisions page opened in a second browser tab) You see a revision for the post content before you started editing, and an autosave revision with the one new char.
+3. add 250+ characters and wait for autosave. Check that permanent revision was created from the previous autosave (+1 char edit).
+4. start editing again from a fully saved state. Add 250+ characters and wait for autosave. Check that permanent revision was not created: the content before the autosave already has a revision and the one created during autosave would be an identical one.
+
 ## 7.5
 
 ### Dashboard