1 files changed, 19 insertions, 5 deletions

diff --git a/app/assets/javascripts/diffs/components/diff_expansion_cell.vue b/app/assets/javascripts/diffs/components/diff_expansion_cell.vue
index 23fbfc2b74b..4eae2e09c08 100644
--- a/app/assets/javascripts/diffs/components/diff_expansion_cell.vue
+++ b/app/assets/javascripts/diffs/components/diff_expansion_cell.vue
@@ -3,7 +3,7 @@ import { mapState, mapActions } from 'vuex';
 import createFlash from '~/flash';
 import { s__ } from '~/locale';
 import Icon from '~/vue_shared/components/icon.vue';
-import { UNFOLD_COUNT } from '../constants';
+import { UNFOLD_COUNT, INLINE_DIFF_VIEW_TYPE, PARALLEL_DIFF_VIEW_TYPE } from '../constants';
 import * as utils from '../store/utils';
 import tooltip from '../../vue_shared/directives/tooltip';
 
@@ -11,6 +11,16 @@ const EXPAND_ALL = 0;
 const EXPAND_UP = 1;
 const EXPAND_DOWN = 2;
 
+const lineNumberByViewType = (viewType, diffLine) => {
+  const numberGetters = {
+    [INLINE_DIFF_VIEW_TYPE]: line => line?.new_line,
+    [PARALLEL_DIFF_VIEW_TYPE]: line => (line?.right || line?.left)?.new_line,
+  };
+  const numberGetter = numberGetters[viewType];
+
+  return numberGetter && numberGetter(diffLine);
+};
+
 export default {
   directives: {
     tooltip,
@@ -67,12 +77,16 @@ export default {
     ...mapActions('diffs', ['loadMoreLines']),
     getPrevLineNumber(oldLineNumber, newLineNumber) {
       const diffFile = utils.findDiffFile(this.diffFiles, this.fileHash);
-      const indexForInline = utils.findIndexInInlineLines(diffFile.highlighted_diff_lines, {
+      const lines = {
+        [INLINE_DIFF_VIEW_TYPE]: diffFile.highlighted_diff_lines,
+        [PARALLEL_DIFF_VIEW_TYPE]: diffFile.parallel_diff_lines,
+      };
+      const index = utils.getPreviousLineIndex(this.diffViewType, diffFile, {
         oldLineNumber,
         newLineNumber,
       });
-      const prevLine = diffFile.highlighted_diff_lines[indexForInline - 2];
-      return (prevLine && prevLine.new_line) || 0;
+
+      return lineNumberByViewType(this.diffViewType, lines[this.diffViewType][index - 2]) || 0;
     },
     callLoadMoreLines(
       endpoint,
@@ -114,7 +128,7 @@ export default {
         this.handleExpandAllLines(expandOptions);
       }
     },
-    handleExpandUpLines(expandOptions = EXPAND_ALL) {
+    handleExpandUpLines(expandOptions) {
       const { endpoint, fileHash, view, oldLineNumber, newLineNumber, offset } = expandOptions;
 
       const bottom = this.isBottom;