Moved Source Editor's theming into utilities

app/assets/javascripts/editor/source_editor.js

-import { editor as monacoEditor, languages as monacoLanguages, Uri } from 'monaco-editor';
+import { editor as monacoEditor, Uri } from 'monaco-editor';
 import { defaultEditorOptions } from '~/ide/lib/editor_options';
 import languages from '~/ide/lib/languages';
-import { DEFAULT_THEME, themes } from '~/ide/lib/themes';
 import { registerLanguages } from '~/ide/utils';
 import { joinPaths } from '~/lib/utils/url_utility';
 import { uuids } from '~/lib/utils/uuids';
@@ -11,7 +10,7 @@ import {
   EDITOR_READY_EVENT,
   EDITOR_TYPE_DIFF,
 } from './constants';
-import { clearDomElement } from './utils';
+import { clearDomElement, setupEditorTheme, getBlobLanguage } from './utils';
 
 export default class SourceEditor {
   constructor(options = {}) {
@@ -22,26 +21,11 @@ export default class SourceEditor {
       ...options,
     };
 
-    SourceEditor.setupMonacoTheme();
+    setupEditorTheme();
 
     registerLanguages(...languages);
   }
 
-  static setupMonacoTheme() {
-    const themeName = window.gon?.user_color_scheme || DEFAULT_THEME;
-    const theme = themes.find((t) => t.name === themeName);
-    if (theme) monacoEditor.defineTheme(themeName, theme.data);
-    monacoEditor.setTheme(theme ? themeName : DEFAULT_THEME);
-  }
-
-  static getModelLanguage(path) {
-    const ext = `.${path.split('.').pop()}`;
-    const language = monacoLanguages
-      .getLanguages()
-      .find((lang) => lang.extensions.indexOf(ext) !== -1);
-    return language ? language.id : 'plaintext';
-  }
-
   static pushToImportsArray(arr, toImport) {
     arr.push(import(toImport));
   }
@@ -124,10 +108,7 @@ export default class SourceEditor {
       return model;
     }
     const diffModel = {
-      original: monacoEditor.createModel(
-        blobOriginalContent,
-        SourceEditor.getModelLanguage(model.uri.path),
-      ),
+      original: monacoEditor.createModel(blobOriginalContent, getBlobLanguage(model.uri.path)),
       modified: model,
     };
     instance.setModel(diffModel);
@@ -155,7 +136,7 @@ export default class SourceEditor {
   };
 
   static instanceUpdateLanguage(inst, path) {
-    const lang = SourceEditor.getModelLanguage(path);
+    const lang = getBlobLanguage(path);
     const model = inst.getModel();
     return monacoEditor.setModelLanguage(model, lang);
   }

app/assets/javascripts/editor/utils.js

+import { editor as monacoEditor, languages as monacoLanguages } from 'monaco-editor';
+import { DEFAULT_THEME, themes } from '~/ide/lib/themes';
+
 export const clearDomElement = (el) => {
   if (!el || !el.firstChild) return;
 
@@ -6,6 +9,22 @@ export const clearDomElement = (el) => {
   }
 };
 
-export default () => ({
-  clearDomElement,
-});
+export const setupEditorTheme = () => {
+  const themeName = window.gon?.user_color_scheme || DEFAULT_THEME;
+  const theme = themes.find((t) => t.name === themeName);
+  if (theme) monacoEditor.defineTheme(themeName, theme.data);
+  monacoEditor.setTheme(theme ? themeName : DEFAULT_THEME);
+};
+
+export const getBlobLanguage = (path) => {
+  const ext = `.${path.split('.').pop()}`;
+  const language = monacoLanguages
+    .getLanguages()
+    .find((lang) => lang.extensions.indexOf(ext) !== -1);
+  return language ? language.id : 'plaintext';
+};
+
+export const setupCodeSnippet = (el) => {
+  monacoEditor.colorizeElement(el);
+  setupEditorTheme();
+};

spec/frontend/editor/utils_spec.js

+import { editor as monacoEditor } from 'monaco-editor';
+import * as utils from '~/editor/utils';
+import { DEFAULT_THEME } from '~/ide/lib/themes';
+
+describe('Source Editor utils', () => {
+  let el;
+
+  const stubUserColorScheme = (value) => {
+    if (window.gon == null) {
+      window.gon = {};
+    }
+    window.gon.user_color_scheme = value;
+  };
+
+  describe('clearDomElement', () => {
+    beforeEach(() => {
+      setFixtures('<div id="foo"><div id="bar">Foo</div></div>');
+      el = document.getElementById('foo');
+    });
+
+    it('removes all child nodes from an element', () => {
+      expect(el.children.length).toBe(1);
+      utils.clearDomElement(el);
+      expect(el.children.length).toBe(0);
+    });
+  });
+
+  describe('setupEditorTheme', () => {
+    beforeEach(() => {
+      jest.spyOn(monacoEditor, 'defineTheme').mockImplementation();
+      jest.spyOn(monacoEditor, 'setTheme').mockImplementation();
+    });
+
+    it.each`
+      themeName            | expectedThemeName
+      ${'solarized-light'} | ${'solarized-light'}
+      ${DEFAULT_THEME}     | ${DEFAULT_THEME}
+      ${'non-existent'}    | ${DEFAULT_THEME}
+    `(
+      'sets the $expectedThemeName theme when $themeName is set in the user preference',
+      ({ themeName, expectedThemeName }) => {
+        stubUserColorScheme(themeName);
+        utils.setupEditorTheme();
+
+        expect(monacoEditor.setTheme).toHaveBeenCalledWith(expectedThemeName);
+      },
+    );
+  });
+
+  describe('getBlobLanguage', () => {
+    it.each`
+      path           | expectedLanguage
+      ${'foo.js'}    | ${'javascript'}
+      ${'foo.js.rb'} | ${'ruby'}
+      ${'foo.bar'}   | ${'plaintext'}
+    `(
+      'sets the $expectedThemeName theme when $themeName is set in the user preference',
+      ({ path, expectedLanguage }) => {
+        const language = utils.getBlobLanguage(path);
+
+        expect(language).toEqual(expectedLanguage);
+      },
+    );
+  });
+
+  describe('setupCodeSnipet', () => {
+    beforeEach(() => {
+      jest.spyOn(monacoEditor, 'colorizeElement').mockImplementation();
+      jest.spyOn(monacoEditor, 'setTheme').mockImplementation();
+      setFixtures('<pre id="foo"></pre>');
+      el = document.getElementById('foo');
+    });
+
+    it('colorizes the element and applies the preference theme', () => {
+      expect(monacoEditor.colorizeElement).not.toHaveBeenCalled();
+      expect(monacoEditor.setTheme).not.toHaveBeenCalled();
+
+      utils.setupCodeSnippet(el);
+
+      expect(monacoEditor.colorizeElement).toHaveBeenCalledWith(el);
+      expect(monacoEditor.setTheme).toHaveBeenCalled();
+    });
+  });
+});