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Rewrite Content Editor development guide

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doc/development/fe_guide/content_editor.md
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
---
# Content Editor **(FREE)**
# Content Editor development guidelines **(FREE)**
The Content Editor is a UI component that provides a WYSIWYG editing
experience for [GitLab Flavored Markdown](../../user/markdown.md) (GFM) in the GitLab application.
experience for [GitLab Flavored Markdown](../../user/markdown.md) in the GitLab application.
It also serves as the foundation for implementing Markdown-focused editors
that target other engines, like static site generators.
......@@ -16,103 +16,324 @@ to build the Content Editor. These frameworks provide a level of abstraction on
the native
[`contenteditable`](https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/Editable_content) web technology.
## Architecture remarks
## Usage guide
At a high level, the Content Editor:
Follow these instructions to include the Content Editor in a feature.
- Imports arbitrary Markdown.
- Renders it in a HTML editing area.
- Exports it back to Markdown with changes introduced by the user.
### Include the Content Editor component
The Content Editor relies on the
[Markdown API endpoint](../../api/markdown.md) to transform Markdown
into HTML. It sends the Markdown input to the REST API and displays the API's
HTML output in the editing area. The editor exports the content back to Markdown
using a client-side library that serializes editable documents into Markdown.
Import the `ContentEditor` Vue component. We recommend using asynchronous named imports to
take advantage of caching as the ContentEditor is a big dependency.
![Content Editor high level diagram](img/content_editor_highlevel_diagram.png)
```html
<script>
export default {
components: {
ContentEditor: () =>
import(
/* webpackChunkName: 'content_editor' */ '~/content_editor/components/content_editor.vue'
),
},
// rest of the component definition
}
</script>
```
Check the [Content Editor technical design document](https://docs.google.com/document/d/1fKOiWpdHned4KOLVOOFYVvX1euEjMP5rTntUhpapdBg)
for more information about the design decisions that drive the development of the editor.
The Content Editor requires two properties:
**NOTE**: We also designed the Content Editor to be extensible. We intend to provide
more information about extension development for supporting new types of content in upcoming
milestones.
- `renderMarkdown` is an asynchronous function that returns the response (String) of invoking the
[Markdown API](../../api/markdown.md).
- `uploadsPath` is a URL that points to a [GitLab upload service](../uploads.md#upload-encodings) with `multipart/form-data` support.
## GitLab Flavored Markdown support
See the [`WikiForm.vue`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/pages/shared/wikis/components/wiki_form.vue#L207) component for a production example of these two properties.
The [GitLab Flavored Markdown](../../user/markdown.md) extends
the [CommonMark specification](https://spec.commonmark.org/0.29/) with support for a
variety of content types like diagrams, math expressions, and tables. Supporting
all GitLab Flavored Markdown content types in the Content Editor is a work in progress. For
the status of the ongoing development for CommonMark and GitLab Flavored Markdown support, read:
### Set and get Markdown
- [Basic Markdown formatting extensions](https://gitlab.com/groups/gitlab-org/-/epics/5404) epic.
- [GitLab Flavored Markdown extensions](https://gitlab.com/groups/gitlab-org/-/epics/5438) epic.
The `ContentEditor` Vue component doesn't implement Vue data binding flow (v-model)
because setting and getting Markdown are expensive operations. Data binding would
trigger these operations every time that the user interacts with the component.
Instead, you should obtain an instance of the `ContentEditor` class by listening to the
`initialized` event.
```html
<script>
import createFlash from '~/flash';
import { __ } from '~/locale';
## Usage
export default {
methods: {
async loadInitialContent(contentEditor) {
this.contentEditor = contentEditor;
To include the Content Editor in your feature, import the `createContentEditor` factory
function and the `ContentEditor` Vue component. `createContentEditor` sets up an instance
of [tiptap's Editor class](https://www.tiptap.dev/api/editor/) with all the necessary
extensions to support editing GitLab Flavored Markdown content. It also creates
a Markdown serializer that allows exporting tiptap's document format to Markdown.
try {
await this.contentEditor.setSerializedContent(this.content);
} catch (e) {
createFlash(__('Could not load initial document'));
}
},
submitChanges() {
const markdown = this.contentEditor.getSerializedContent();
},
},
};
</script>
<template>
<content-editor
:render-markdown="renderMarkdown"
:uploads-path="pageInfo.uploadsPath"
@initialized="loadInitialContent"
/>
</template>
```
`createContentEditor` requires a `renderMarkdown` parameter invoked
by the editor every time it needs to convert Markdown to HTML. The Content Editor
does not provide a default value for this function yet.
### Listen for changes
**NOTE**: The Content Editor is in an early development stage. Usage and development
guidelines are subject to breaking changes in the upcoming months.
You can still react to changes in the Content Editor. Reacting to changes helps
you know if the document is empty or dirty. Use `@change` event handler for
this purpose.
```html
<script>
import { GlButton } from '@gitlab/ui';
import { createContentEditor, ContentEditor } from '~/content_editor';
import { __ } from '~/locale';
import createFlash from '~/flash';
export default {
data() {
return {
empty: false,
};
},
methods: {
handleContentEditorChange({ empty }) {
this.empty = empty;
}
},
};
</script>
<template>
<div>
<content-editor
:render-markdown="renderMarkdown"
:uploads-path="pageInfo.uploadsPath"
@initialized="loadInitialContent"
@change="handleContentEditorChange"
/>
<gl-button :disabled="empty" @click="submitChanges">
{{ __('Submit changes') }}
</gl-button>
</div>
</template>
```
## Implementation guide
The Content Editor is composed of three main layers:
- The editing tools UI like the toolbar and the table structure editor. They
display the editor's state and mutate it by dispatching commands.
- The Tiptap Editor object manages the editor's state,
and expose business logic as commands executed by the editing tools UI.
- The Markdown serializer transforms a Markdown source string into a ProseMirror
document and vice versa.
### Editing tools UI
The editing tools UI are Vue components that display the editor's state and
dispatch [commands](https://www.tiptap.dev/api/commands/#commands) to mutate it.
They are located in the `~/content_editor/components` directory. For example,
the **Bold** toolbar button displays the editor's state by becoming active when
the user selects bold text. This button also dispatches the `toggleBold` command
to format text as bold.
```mermaid
sequenceDiagram
participant A as Editing tools UI
participant B as Tiptap object
A->>B: queries state/dispatches commands
B--)A: notifies state changes
```
#### Node views
We implement [node views](https://www.tiptap.dev/guide/node-views/vue/#node-views-with-vue)
to provide inline editing tools for some content types like tables and images. Node views
allow separating the presentation of a content type from its
[model](https://prosemirror.net/docs/guide/#doc.data_structures). Using a Vue component in
the presentation layer enables sophisticated editing experiences in the Content Editor.
Node views are located in `~/content_editor/components/wrappers`.
#### Dispatch commands
You can inject the Tiptap Editor object to Vue components to dispatch
commands. **notice**: Do not implement logic that changes the editor's
state in Vue components. Encapsulate this logic in commands and dispatch
the command from the component's methods.
```html
<script>
export default {
inject: ['tiptapEditor'],
methods: {
execute() {
//Incorrect
const { state, view } = this.tiptapEditor.state;
const { tr, schema } = state;
tr.addMark(state.selection.from, state.selection.to, null, null, schema.mark('bold'));
// Correct
this.tiptapEditor.chain().toggleBold().focus().run();
},
}
};
</script>
<template>
```
#### Query editor's state
Use the `EditorStateObserver` renderless component to react to changes in the
editor's state like when the document or the selection changes. You can listen to
the following events: `docUpdate`, `selectionUpdate`, `transaction`, `focus`, `blur`,
and `error`. Learn more about these events in
[Tiptap's event guide](https://www.tiptap.dev/api/events/).
```html
<script>
// Parts of the code has been hidden for efficiency
import EditorStateObserver from './editor_state_observer.vue';
export default {
components: {
ContentEditor,
GlButton,
EditorStateObserver,
},
data() {
return {
contentEditor: null,
}
},
created() {
this.contentEditor = createContentEditor({
renderMarkdown: (markdown) => Api.markdown({ text: markdown }),
});
try {
await this.contentEditor.setSerializedContent(this.content);
} catch (e) {
createFlash({
message: __('There was an error loading content in the editor'), error: e
});
}
error: null,
};
},
methods: {
async save() {
await Api.updateContent({
content: this.contentEditor.getSerializedContent(),
});
displayError({ message }) {
this.error = message;
},
dismissError() {
this.error = null;
},
},
};
</script>
<template>
<div>
<content-editor :content-editor="contentEditor" />
<gl-button @click="save()">Save</gl-button>
</div>
<editor-state-observer @error="displayError">
<gl-alert v-if="error" class="gl-mb-6" variant="danger" @dismiss="dismissError">
{{ error }}
</gl-alert>
</editor-state-observer>
</template>
```
Call `setSerializedContent` to set initial Markdown in the Editor. This method is
asynchronous because it makes an API request to render the Markdown input.
`getSerializedContent` returns a Markdown string that represents the serialized
version of the editable document.
### The Tiptap editor object
The Tiptap [Editor](https://www.tiptap.dev/api/editor) class manages
the editor's state and encapsulates all the business logic that powers
the Content Editor. The Content Editor takes care of constructing a
new instance of this class and providing all the necessary extensions to support
[GitLab Flavored Markdown](../../user/markdown.md).
#### Implement new extensions
Extensions are the building blocks of the Content Editor. You can learn how to implement
new ones by reading [Tiptap's guide](https://www.tiptap.dev/guide/custom-extensions).
We recommend checking the list of built-in [nodes](https://www.tiptap.dev/api/nodes) and
[marks](https://www.tiptap.dev/api/marks) before implementing a new extension
from scratch.
You should store the Content Editor extensions in the
`~/content_editor/extensions` directory. When using a Tiptap's built-in
extension, wrap it in a ES6 module inside this directory.
```javascript
export { Bold as default } from '@tiptap/extension-bold';
```
Use the `extend` method to customize the Extension's behavior
```javascript
import { HardBreak } from '@tiptap/extension-hard-break';
export default HardBreak.extend({
addKeyboardShortcuts() {
return {
'Shift-Enter': () => this.editor.commands.setHardBreak(),
};
},
});
```
#### Register extensions
Register the new extension in `~/content_editor/services/create_content_editor.js`. Import
the extension module and add it to the `builtInContentEditorExtensions` array.
```javascript
import Emoji from '../extensions/emoji';
const builtInContentEditorExtensions = [
Code,
CodeBlockHighlight,
Document,
Dropcursor,
Emoji,
// Other extensions
```
### The Markdown serializer
The Markdown Serializer transforms a Markdown String to a
[ProseMirror document](https://prosemirror.net/docs/guide/#doc) and vice versa.
#### Deserialization
Deserialization is the process of converting Markdown to a ProseMirror document.
We take advantage of ProseMirror's
[HTML parsing and serialization capabilities](https://prosemirror.net/docs/guide/#schema.serialization_and_parsing)
by first rendering the Markdown as HTML using the [Markdown API endpoint](../../api/markdown.md).
```mermaid
sequenceDiagram
participant A as Content Editor
participant E as Tiptap Object
participant B as Markdown Serializer
participant C as Markdown API
participant D as ProseMirror Parser
A->>B: deserialize(markdown)
B->>C: render(markdown)
C-->>B: html
B->>D: to document(html)
D-->>A: document
A->>E: setContent(document)
```
Deserializers live in the extension modules. Read Tiptap's
[parseHTML](https://www.tiptap.dev/guide/custom-extensions#parse-html) and
[addAttributes](https://www.tiptap.dev/guide/custom-extensions#attributes) documentation to
learn how to implement them. Titap's API is a wrapper around ProseMirror's
[schema spec API](https://prosemirror.net/docs/ref/#model.SchemaSpec).
#### Serialization
Serialization is the process of converting a ProseMirror document to Markdown. The Content
Editor uses [`prosemirror-markdown`](https://github.com/ProseMirror/prosemirror-markdown)
to serialize documents. We recommend reading the
[MarkdownSerializer](https://github.com/ProseMirror/prosemirror-markdown#class-markdownserializer)
and [MarkdownSerializerState](https://github.com/ProseMirror/prosemirror-markdown#class-markdownserializerstate)
classes documentation before implementing a serializer.
```mermaid
sequenceDiagram
participant A as Content Editor
participant B as Markdown Serializer
participant C as ProseMirror Markdown
A->>B: serialize(document)
B->>C: serialize(document, serializers)
C-->>A: markdown string
```
`prosemirror-markdown` requires implementing a serializer function for each content type supported
by the Content Editor. We implement serializers in `~/content_editor/services/markdown_serializer.js`.
Markdown is supported
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