1 files changed, 118 insertions, 51 deletions

diff --git a/app/assets/javascripts/vue_shared/components/source_viewer/source_viewer.vue b/app/assets/javascripts/vue_shared/components/source_viewer/source_viewer.vue
index 4a78cbacec0..edf2229a9a1 100644
--- a/app/assets/javascripts/vue_shared/components/source_viewer/source_viewer.vue
+++ b/app/assets/javascripts/vue_shared/components/source_viewer/source_viewer.vue
@@ -1,16 +1,22 @@
 <script>
 import { GlSafeHtmlDirective, GlLoadingIcon } from '@gitlab/ui';
-import LineNumbers from '~/vue_shared/components/line_numbers.vue';
-import { sanitize } from '~/lib/dompurify';
-import { ROUGE_TO_HLJS_LANGUAGE_MAP } from './constants';
-import { wrapLines } from './utils';
-
-const LINE_SELECT_CLASS_NAME = 'hll';
+import LineHighlighter from '~/blob/line_highlighter';
+import eventHub from '~/notes/event_hub';
+import { ROUGE_TO_HLJS_LANGUAGE_MAP, LINES_PER_CHUNK } from './constants';
+import Chunk from './components/chunk.vue';
 
+/*
+ * This component is optimized to handle source code with many lines of code by splitting source code into chunks of 70 lines of code,
+ * we highlight and display the 1st chunk (L1-70) to the user as quickly as possible.
+ *
+ * The rest of the lines (L71+) is rendered once the browser goes into an idle state (requestIdleCallback).
+ * Each chunk is self-contained, this ensures when for example the width of a container on line 1000 changes,
+ * it does not trigger a repaint on a parent element that wraps all 1000 lines.
+ */
 export default {
   components: {
-    LineNumbers,
     GlLoadingIcon,
+    Chunk,
   },
   directives: {
     SafeHtml: GlSafeHtmlDirective,
@@ -27,46 +33,94 @@ export default {
       content: this.blob.rawTextBlob,
       language: ROUGE_TO_HLJS_LANGUAGE_MAP[this.blob.language],
       hljs: null,
+      firstChunk: null,
+      chunks: {},
+      isLoading: true,
+      isLineSelected: false,
+      lineHighlighter: null,
     };
   },
   computed: {
+    splitContent() {
+      return this.content.split('\n');
+    },
     lineNumbers() {
-      return this.content.split('\n').length;
+      return this.splitContent.length;
     },
-    highlightedContent() {
-      let highlightedContent;
-      let { language } = this;
+  },
+  async created() {
+    this.generateFirstChunk();
+    this.hljs = await this.loadHighlightJS();
 
-      if (this.hljs) {
-        if (!language) {
-          const hljsHighlightAuto = this.hljs.highlightAuto(this.content);
+    if (this.language) {
+      this.languageDefinition = await this.loadLanguage();
+    }
 
-          highlightedContent = hljsHighlightAuto.value;
-          language = hljsHighlightAuto.language;
-        } else if (this.languageDefinition) {
-          highlightedContent = this.hljs.highlight(this.content, { language: this.language }).value;
-        }
+    // Highlight the first chunk as soon as highlight.js is available
+    this.highlightChunk(null, true);
+
+    window.requestIdleCallback(async () => {
+      // Generate the remaining chunks once the browser idles to ensure the browser resources are spent on the most important things first
+      this.generateRemainingChunks();
+      this.isLoading = false;
+      await this.$nextTick();
+      this.lineHighlighter = new LineHighlighter({ scrollBehavior: 'auto' });
+    });
+  },
+  methods: {
+    generateFirstChunk() {
+      const lines = this.splitContent.splice(0, LINES_PER_CHUNK);
+      this.firstChunk = this.createChunk(lines);
+    },
+    generateRemainingChunks() {
+      const result = {};
+      for (let i = 0; i < this.splitContent.length; i += LINES_PER_CHUNK) {
+        const chunkIndex = Math.floor(i / LINES_PER_CHUNK);
+        const lines = this.splitContent.slice(i, i + LINES_PER_CHUNK);
+        result[chunkIndex] = this.createChunk(lines, i + LINES_PER_CHUNK);
       }
 
-      return wrapLines(highlightedContent, language);
+      this.chunks = result;
     },
-  },
-  watch: {
-    highlightedContent() {
-      this.$nextTick(() => this.selectLine());
+    createChunk(lines, startingFrom = 0) {
+      return {
+        content: lines.join('\n'),
+        startingFrom,
+        totalLines: lines.length,
+        language: this.language,
+        isHighlighted: false,
+      };
     },
-    $route() {
+    highlightChunk(index, isFirstChunk) {
+      const chunk = isFirstChunk ? this.firstChunk : this.chunks[index];
+
+      if (chunk.isHighlighted) {
+        return;
+      }
+
+      const { highlightedContent, language } = this.highlight(chunk.content, this.language);
+
+      Object.assign(chunk, { language, content: highlightedContent, isHighlighted: true });
+
       this.selectLine();
+
+      this.$nextTick(() => eventHub.$emit('showBlobInteractionZones', this.blob.path));
     },
-  },
-  async mounted() {
-    this.hljs = await this.loadHighlightJS();
+    highlight(content, language) {
+      let detectedLanguage = language;
+      let highlightedContent;
+      if (this.hljs) {
+        if (!detectedLanguage) {
+          const hljsHighlightAuto = this.hljs.highlightAuto(content);
+          highlightedContent = hljsHighlightAuto.value;
+          detectedLanguage = hljsHighlightAuto.language;
+        } else if (this.languageDefinition) {
+          highlightedContent = this.hljs.highlight(content, { language: this.language }).value;
+        }
+      }
 
-    if (this.language) {
-      this.languageDefinition = await this.loadLanguage();
-    }
-  },
-  methods: {
+      return { highlightedContent, language: detectedLanguage };
+    },
     loadHighlightJS() {
       // If no language can be mapped to highlight.js we load all common languages else we load only the core (smallest footprint)
       return !this.language ? import('highlight.js/lib/common') : import('highlight.js/lib/core');
@@ -83,21 +137,14 @@ export default {
 
       return languageDefinition;
     },
-    selectLine() {
-      const hash = sanitize(this.$route.hash);
-      const lineToSelect = hash && this.$el.querySelector(hash);
-
-      if (!lineToSelect) {
+    async selectLine() {
+      if (this.isLineSelected || !this.lineHighlighter) {
         return;
       }
 
-      if (this.$options.currentlySelectedLine) {
-        this.$options.currentlySelectedLine.classList.remove(LINE_SELECT_CLASS_NAME);
-      }
-
-      lineToSelect.classList.add(LINE_SELECT_CLASS_NAME);
-      this.$options.currentlySelectedLine = lineToSelect;
-      lineToSelect.scrollIntoView({ behavior: 'smooth', block: 'center' });
+      this.isLineSelected = true;
+      await this.$nextTick();
+      this.lineHighlighter.highlightHash(this.$route.hash);
     },
   },
   userColorScheme: window.gon.user_color_scheme,
@@ -105,16 +152,36 @@ export default {
 };
 </script>
 <template>
-  <gl-loading-icon v-if="!highlightedContent" size="sm" class="gl-my-5" />
   <div
-    v-else
-    class="file-content code js-syntax-highlight blob-content gl-display-flex"
+    class="file-content code js-syntax-highlight blob-content gl-display-flex gl-flex-direction-column gl-overflow-auto"
     :class="$options.userColorScheme"
     data-type="simple"
+    :data-path="blob.path"
     data-qa-selector="blob_viewer_file_content"
   >
-    <line-numbers :lines="lineNumbers" />
-    <pre class="code highlight gl-pb-0!"><code v-safe-html="highlightedContent"></code>
-    </pre>
+    <chunk
+      v-if="firstChunk"
+      :lines="firstChunk.lines"
+      :total-lines="firstChunk.totalLines"
+      :content="firstChunk.content"
+      :starting-from="firstChunk.startingFrom"
+      :is-highlighted="firstChunk.isHighlighted"
+      :language="firstChunk.language"
+    />
+
+    <gl-loading-icon v-if="isLoading" size="sm" class="gl-my-5" />
+    <chunk
+      v-for="(chunk, key, index) in chunks"
+      v-else
+      :key="key"
+      :lines="chunk.lines"
+      :content="chunk.content"
+      :total-lines="chunk.totalLines"
+      :starting-from="chunk.startingFrom"
+      :is-highlighted="chunk.isHighlighted"
+      :chunk-index="index"
+      :language="chunk.language"
+      @appear="highlightChunk"
+    />
   </div>
 </template>