Try to resolve edit conflicts

The most common case of edit conflicts on talk pages is several people
responding to the same comment at the same time.[citation needed]

We can easily resolve this case by fetching the latest revision of the
page and re-running our code to insert a reply on it.

When we can't insert a reply, that probably means the parent comment
was deleted or moved, so display an error message indicating that
instead of the generic one.

Bug: T240643
Change-Id: Ic686acc747580d46779960211a02e9830a6ae86f

extension.json

@@ -58,6 +58,7 @@
 				"ext.discussionTools.modifier"
 			],
 			"messages": [
+				"discussiontools-error-comment-disappeared",
 				"discussiontools-defaultsummary-reply",
 				"discussiontools-replylink",
 				"discussiontools-replywidget-loading"

i18n/en.json

@@ -12,6 +12,7 @@
 	"discussiontools-replywidget-preview": "Preview",
 	"discussiontools-replywidget-reply": "Reply",
 	"discussiontools-replywidget-terms-click": "By clicking \"$1\", you agree to the terms of use for this wiki.",
+	"discussiontools-error-comment-disappeared": "Could not find the comment you're replying to on the page. It might have been deleted or moved to another page. Please reload the page and try again.",
 	"tag-discussiontools": "DiscussionTools edit",
 	"tag-discussiontools-description": "Edit made using DiscussionTools",
 	"tag-discussiontools-edit": "edited comment",

i18n/qqq.json

@@ -16,6 +16,7 @@
 	"discussiontools-replywidget-preview": "Label for the preview area of the reply widget",
 	"discussiontools-replywidget-reply": "Label for the button to submit a reply in the reply widget",
 	"discussiontools-replywidget-terms-click": "Terms of use for posting a reply.\n\n* $1 is the label of the button to be clicked, e.g. {{msg-mw|discussiontools-replywidget-reply}}.",
+	"discussiontools-error-comment-disappeared": "Error message.",
 	"tag-discussiontools": "Short description of the discussiontools tag.\n\nShown on lists of changes (history, recentchanges, etc.) for each edit made using DiscussionTools.\n\nSee also:\n* {{msg-mw|Tag-discussiontools-description}}",
 	"tag-discussiontools-description": "Long description of the discussiontools tag ({{msg-mw|Tag-discussiontools}}).\n\nShown on [[Special:Tags]].\n\nSee also:\n* {{msg-mw|Tag-discussiontools}}",
 	"tag-discussiontools-edit": "Short description of the discussiontools-edit tag.\n\nShown on lists of changes (history, recentchanges, etc.) for each edit to an existing comment made using DiscussionTools.\n\nThis message is always shown directly after {{msg-mw|tag-discussiontools}} and a comma.\n\nSee also:\n* {{msg-mw|Tag-discussiontools-edit-description}}\n* {{Related|tag-discussiontools}}",

modules/controller.js

@@ -212,7 +212,10 @@ function getParsoidCommentData( pageName, oldId, commentId ) {
 			parsoidCommentsById = commentsById( parsoidComments );
 
 			if ( !parsoidCommentsById[ commentId ] ) {
-				throw new Error( 'Could not find comment in Parsoid HTML' );
+				return $.Deferred().reject( 'comment-disappeared', { errors: [ {
+					code: 'comment-disappeared',
+					html: mw.message( 'discussiontools-error-comment-disappeared' ).parse()
+				} ] } ).promise();
 			}
 
 			return {

modules/dt.ui.ReplyWidget.js

@@ -253,6 +253,30 @@ ReplyWidget.prototype.onReplyClick = function () {
 	// We must get a new copy of the document every time, otherwise any unsaved replies will pile up
 	this.getParsoidCommentData().then( function ( parsoidData ) {
 		return controller.postReply( widget, parsoidData );
+	} ).catch( function ( code, data ) {
+		// Handle edit conflicts. Load the latest revision of the page, then try again. If the parent
+		// comment has been deleted from the page, or if retry also fails for some other reason, the
+		// error is handled as normal below.
+		if ( code === 'editconflict' ) {
+			return widget.api.get( {
+				action: 'query',
+				prop: 'revisions',
+				rvprop: 'ids',
+				rvlimit: 1,
+				titles: mw.config.get( 'wgRelevantPageName' ),
+				formatversion: 2
+			} ).then( function ( resp ) {
+				var latestRevId = resp.query.pages[ 0 ].revisions[ 0 ].revid;
+				mw.config.set( {
+					wgCurRevisionId: latestRevId,
+					wgRevisionId: latestRevId
+				} );
+				return widget.getParsoidCommentData().then( function ( parsoidData ) {
+					return controller.postReply( widget, parsoidData );
+				} );
+			} );
+		}
+		return $.Deferred().reject( code, data ).promise();
 	} ).then( function ( data ) {
 		// eslint-disable-next-line no-jquery/no-global-selector
 		var $container = $( '#mw-content-text' );
@@ -279,7 +303,7 @@ ReplyWidget.prototype.onReplyClick = function () {
 	}, function ( code, data ) {
 		widget.errorMessage = new OO.ui.MessageWidget( {
 			type: 'error',
-			label: ( new mw.Api() ).getErrorMessage( data )
+			label: widget.api.getErrorMessage( data )
 		} );
 		widget.errorMessage.$element.insertBefore( widget.replyBodyWidget.$element );
 	} ).always( function () {