Mark diff files if they're part of broken symlinks

- Also begins moving Diff File-specific things to file
     just for Diff Files instead of dumping everything
    into the `utils.js` junk drawer.

app/assets/javascripts/diffs/constants.js

@@ -36,6 +36,9 @@ export const LENGTH_OF_AVATAR_TOOLTIP = 17;
 export const LINES_TO_BE_RENDERED_DIRECTLY = 100;
 export const MAX_LINES_TO_BE_RENDERED = 2000;
 
+export const DIFF_FILE_SYMLINK_MODE = '120000';
+export const DIFF_FILE_DELETED_MODE = '0';
+
 export const MR_TREE_SHOW_KEY = 'mr_tree_show';
 
 export const TREE_TYPE = 'tree';

app/assets/javascripts/diffs/diff_file.js

+import { DIFF_FILE_SYMLINK_MODE, DIFF_FILE_DELETED_MODE } from './constants';
+
+function fileSymlinkInformation(file, fileList) {
+  const duplicates = fileList.filter(iteratedFile => iteratedFile.file_hash === file.file_hash);
+  const includesSymlink = duplicates.some(iteratedFile => {
+    return [iteratedFile.a_mode, iteratedFile.b_mode].includes(DIFF_FILE_SYMLINK_MODE);
+  });
+  const brokenSymlinkScenario = duplicates.length > 1 && includesSymlink;
+
+  return (
+    brokenSymlinkScenario && {
+      replaced: file.b_mode === DIFF_FILE_DELETED_MODE,
+      wasSymbolic: file.a_mode === DIFF_FILE_SYMLINK_MODE,
+      isSymbolic: file.b_mode === DIFF_FILE_SYMLINK_MODE,
+      wasReal: ![DIFF_FILE_SYMLINK_MODE, DIFF_FILE_DELETED_MODE].includes(file.a_mode),
+      isReal: ![DIFF_FILE_SYMLINK_MODE, DIFF_FILE_DELETED_MODE].includes(file.b_mode),
+    }
+  );
+}
+
+/* eslint-disable-next-line import/prefer-default-export */
+export function prepareRawDiffFile({ file, allFiles }) {
+  Object.assign(file, {
+    brokenSymlink: fileSymlinkInformation(file, allFiles),
+  });
+
+  return file;
+}

app/assets/javascripts/diffs/store/utils.js

@@ -18,6 +18,7 @@ import {
   SHOW_WHITESPACE,
   NO_SHOW_WHITESPACE,
 } from '../constants';
+import { prepareRawDiffFile } from '../diff_file';
 
 export function findDiffFile(files, match, matchKey = 'file_hash') {
   return files.find(file => file[matchKey] === match);
@@ -294,9 +295,10 @@ function cleanRichText(text) {
   return text ? text.replace(/^[+ -]/, '') : undefined;
 }
 
-function prepareLine(line) {
+function prepareLine(line, file) {
   if (!line.alreadyPrepared) {
     Object.assign(line, {
+      commentsDisabled: file.brokenSymlink,
       rich_text: cleanRichText(line.rich_text),
       discussionsExpanded: true,
       discussions: [],
@@ -330,7 +332,7 @@ export function prepareLineForRenamedFile({ line, diffViewType, diffFile, index
     old_line: lineNumber,
   };
 
-  prepareLine(cleanLine); // WARNING: In-Place Mutations!
+  prepareLine(cleanLine, diffFile); // WARNING: In-Place Mutations!
 
   if (diffViewType === PARALLEL_DIFF_VIEW_TYPE) {
     return {
@@ -348,19 +350,19 @@ function prepareDiffFileLines(file) {
   const parallelLines = file.parallel_diff_lines;
   let parallelLinesCount = 0;
 
-  inlineLines.forEach(prepareLine);
+  inlineLines.forEach(line => prepareLine(line, file)); // WARNING: In-Place Mutations!
 
   parallelLines.forEach((line, index) => {
     Object.assign(line, { line_code: getLineCode(line, index) });
 
     if (line.left) {
       parallelLinesCount += 1;
-      prepareLine(line.left);
+      prepareLine(line.left, file); // WARNING: In-Place Mutations!
     }
 
     if (line.right) {
       parallelLinesCount += 1;
-      prepareLine(line.right);
+      prepareLine(line.right, file); // WARNING: In-Place Mutations!
     }
   });
 
@@ -407,6 +409,7 @@ function deduplicateFilesList(files) {
 
 export function prepareDiffData(diff, priorFiles = []) {
   const cleanedFiles = (diff.diff_files || [])
+    .map((file, index, allFiles) => prepareRawDiffFile({ file, allFiles }))
     .map(ensureBasicDiffFileLines)
     .map(prepareDiffFileLines)
     .map(finalizeDiffFile);