Add filetree on left of diff view (#21012)

This PR adds a filetree to the left side of the files/diff view.

Initially the filetree will not be shown and may be shown via a new
"Show file tree" button.

Showing and hiding is using the same icon as github. Folders are
collapsible. On small devices (max-width 991 PX) the file tree will be
hidden.

Close #18192

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/components/DiffFileTree.vue

@@ -0,0 +1,129 @@
+<template>
+  <div
+    v-show="fileTreeIsVisible"
+    id="diff-file-tree"
+    class="mr-3 mt-3 diff-detail-box"
+  >
+    <!-- only render the tree if we're visible. in many cases this is something that doesn't change very often -->
+    <div class="ui list" v-if="fileTreeIsVisible">
+      <DiffFileTreeItem v-for="item in fileTree" :key="item.name" :item="item" />
+    </div>
+    <div v-if="isIncomplete" id="diff-too-many-files-stats" class="pt-2">
+      <span>{{ tooManyFilesMessage }}</span><a :class="['ui', 'basic', 'tiny', 'button', isLoadingNewData === true ? 'disabled' : '']" id="diff-show-more-files-stats" @click.stop="loadMoreData">{{ showMoreMessage }}</a>
+    </div>
+  </div>
+</template>
+
+<script>
+import DiffFileTreeItem from './DiffFileTreeItem.vue';
+import {doLoadMoreFiles} from '../features/repo-diff.js';
+
+const {pageData} = window.config;
+const LOCAL_STORAGE_KEY = 'diff_file_tree_visible';
+
+export default {
+  name: 'DiffFileTree',
+  components: {DiffFileTreeItem},
+
+  data: () => {
+    const fileTreeIsVisible = localStorage.getItem(LOCAL_STORAGE_KEY) === 'true';
+    pageData.diffFileInfo.fileTreeIsVisible = fileTreeIsVisible;
+    return pageData.diffFileInfo;
+  },
+
+  computed: {
+    fileTree() {
+      const result = [];
+      for (const file of this.files) {
+        // Split file into directories
+        const splits = file.Name.split('/');
+        let index = 0;
+        let parent = null;
+        let isFile = false;
+        for (const split of splits) {
+          index += 1;
+          // reached the end
+          if (index === splits.length) {
+            isFile = true;
+          }
+          let newParent = {
+            name: split,
+            children: [],
+            isFile
+          };
+
+          if (isFile === true) {
+            newParent.file = file;
+          }
+
+          if (parent) {
+            // check if the folder already exists
+            const existingFolder = parent.children.find(
+              (x) => x.name === split
+            );
+            if (existingFolder) {
+              newParent = existingFolder;
+            } else {
+              parent.children.push(newParent);
+            }
+          } else {
+            const existingFolder = result.find((x) => x.name === split);
+            if (existingFolder) {
+              newParent = existingFolder;
+            } else {
+              result.push(newParent);
+            }
+          }
+          parent = newParent;
+        }
+      }
+      const mergeChildIfOnlyOneDir = (entries) => {
+        for (const entry of entries) {
+          if (entry.children) {
+            mergeChildIfOnlyOneDir(entry.children);
+          }
+          if (entry.children.length === 1 && entry.children[0].isFile === false) {
+            // Merge it to the parent
+            entry.name = `${entry.name}/${entry.children[0].name}`;
+            entry.children = entry.children[0].children;
+          }
+        }
+      };
+      // Merge folders with just a folder as children in order to
+      // reduce the depth of our tree.
+      mergeChildIfOnlyOneDir(result);
+      return result;
+    }
+  },
+
+  mounted() {
+    // ensure correct buttons when we are mounted to the dom
+    this.adjustToggleButton(this.fileTreeIsVisible);
+    document.querySelector('.diff-toggle-file-tree-button').addEventListener('click', this.toggleVisibility);
+  },
+  unmounted() {
+    document.querySelector('.diff-toggle-file-tree-button').removeEventListener('click', this.toggleVisibility);
+  },
+  methods: {
+    toggleVisibility() {
+      this.updateVisibility(!this.fileTreeIsVisible);
+    },
+    updateVisibility(visible) {
+      this.fileTreeIsVisible = visible;
+      localStorage.setItem(LOCAL_STORAGE_KEY, this.fileTreeIsVisible);
+      this.adjustToggleButton(this.fileTreeIsVisible);
+    },
+    adjustToggleButton(visible) {
+      const [toShow, toHide] = document.querySelectorAll('.diff-toggle-file-tree-button .icon');
+      toShow.classList.toggle('hide', visible);  // hide the toShow icon if the tree is visible
+      toHide.classList.toggle('hide', !visible); // similarly
+    },
+    loadMoreData() {
+      this.isLoadingNewData = true;
+      doLoadMoreFiles(this.link, this.diffEnd, () => {
+        this.isLoadingNewData = false;
+      });
+    }
+  },
+};
+</script>