fix assumption

Author: wxiaoguang

services/gitdiff/gitdiff.go

@@ -224,7 +224,8 @@ func FillHiddenCommentIDsForDiffLine(line *DiffLine, lineComments map[int64][]*i
 	var hiddenCommentIDs []int64
 	for commentLineNum, comments := range lineComments {
 		if commentLineNum < 0 {
-			continue // Skip left-side, unchanged lines always use "right (proposed)" side for comments
+			// ATTENTION: BLOB-EXCERPT-COMMENT-RIGHT: skip left-side, unchanged lines always use "right (proposed)" side for comments
+			continue
 		}
 		lineNum := int(commentLineNum)
 		isEndOfFileExpansion := line.SectionInfo.RightHunkSize == 0

templates/repo/diff/blob_excerpt.tmpl

@@ -15,8 +15,9 @@
 			<td class="lines-escape lines-escape-old">{{if and $line.LeftIdx $inlineDiff.EscapeStatus.Escaped}}<button class="toggle-escape-button btn interact-bg" title="{{template "repo/diff/escape_title" dict "diff" $inlineDiff}}"></button>{{end}}</td>
 			<td class="lines-type-marker lines-type-marker-old">{{if $line.LeftIdx}}<span class="tw-font-mono" data-type-marker=""></span>{{end}}</td>
 			<td class="lines-code lines-code-old">
-				{{- if and $canCreateComment $line.LeftIdx -}}
-					<button type="button" aria-label="{{ctx.Locale.Tr "repo.diff.comment.add_line_comment"}}" class="ui primary button add-code-comment add-code-comment-left{{if (not $line.CanComment)}} tw-invisible{{end}}" data-side="left" data-idx="{{$line.LeftIdx}}">
+				{{/* ATTENTION: BLOB-EXCERPT-COMMENT-RIGHT: here it intentially use "right" side to comment, because the backend code depends on the assumption that the comment only happens on right side*/}}
+				{{- if and $canCreateComment $line.RightIdx -}}
+					<button type="button" aria-label="{{ctx.Locale.Tr "repo.diff.comment.add_line_comment"}}" class="ui primary button add-code-comment add-code-comment-right{{if (not $line.CanComment)}} tw-invisible{{end}}" data-side="right" data-idx="{{$line.RightIdx}}">
 						{{- svg "octicon-plus" -}}
 					</button>
 				{{- end -}}