Tree View Protocol

Metals implements a Language Server Protocol extension called the "Tree View Protocol" to render tree views in the editor client.

Base data structures

Tree View

One "tree view" represents the root of a tree along with all of its descendent tree nodes. Multiple tree views can be displayed at the same time in an editor client.

A tree view is uniquely identified by a viewId: string field in other data structures.

Tree View Node

A tree view can contain multiple tree view nodes. A tree view node can have the following metadata.

interface TreeViewNode {
  /** The ID of the view that this node is associated with. */
  viewId: string;
  /** The URI of this node, or undefined if node is a root of the tree. */
  nodeUri?: string;
  /** The title to display for this node. */
  label: string;
  /** An optional command to trigger when the user clicks on node. */
  command?: Command;
  /** An optional SVG icon to display next to the label of this node. */
  icon?: string;
  /** An optional description of this node that is displayed when the user hovers over this node. */
  tooltip?: string;
  /**
   * Whether this tree node should be collapsed, expanded or if it has no children.
   *
   * - undefined: this node has no children.
   * - collapsed: this node has children and this node should be auto-expanded
   *   on the first load.
   * - expanded: this node has children and the user should manually expand
   *   this node to see the children.
   */
  collapseState?: "expanded" | "collapsed";
}

The children of a tree view node can be obtained through the metals/treeViewChildren request.

Tree View Command

/**
 * A command to execute on the client when the user clicks on a tree view node.
 */
interface TreeViewCommand {
  /** The title of the command, the client is free to not display this title in the UI. */
  title: string;
  /** The identifier of the command that should be executed by the client. */
  command: string;
  /** A description of what this command does. */
  tooltip?: string;
  /** Optional arguments to invoke the command with. */
  arguments?: any[];
}

Endpoints

The Tree View Protocol (TVP) consists of several JSON-RPC requests and notification endpoints.

initialize

The Tree View Protocol is only enabled when both the client and server declare support for the protocol by adding an treeViewProvider: true field to the experimental section of the server and client capabilities in the initialize response.

{
  "capabilities": {
    "experimental": {
      "treeViewProvider": true
    }
  }
}

metals/treeViewChildren

The tree view children request is sent from the client to the server to get the children nodes of a tree view node. The client is safe to cache the response of the children until server sends a metals/treeViewDidChange notification for the parent node or one of its ancestor nodes.

Request:

• method: metals/treeViewChildren
• params: TreeViewChildrenParams defined as follows.

interface TreeViewChildrenParams {
  /** The ID of the view that this node is associated with. */
  viewId: string;
  /** The URI of the parent node or undefined when listing the root node. */
  nodeUri?: string;
}

Response:

• result: TreeViewChildrenResult defined as follows.

interface TreeViewChildrenResult {
  /** The child nodes of the requested parent node. */
  nodes: TreeViewNode[];
}

metals/treeViewParent

The tree view parent request is sent from the client to the server to obtain the parent node of a child node. The metals/treeViewParent endpoint is required to support metals/treeViewReveal.

Request:

• method: metals/treeViewParent
• params: TreeViewParentParams defined as follows.

interface TreeViewParentParams {
  /** The ID of the view that the nodeUri is associated with. */
  viewId: string;
  /** The URI of the child node. */
  nodeUri: string;
}

Response:

• result: TreeViewParentResult defined as follows.

interface TreeViewParentResult {
  /** The parent node URI or undefined when the parent is the root node. */
  uri?: string;
}

metals/treeViewDidChange

The tree view did change notification is sent from the server to the client to notify that the metadata about a given tree view node has changed.

Notification:

• method: metals/treeViewVisibilityDidChange
• params: TreeViewDidChangeParams defined as follows:

interface TreeViewDidChangeParams {
  /** The nodes that have changed. */
  nodes: TreeViewNode[];
}

metals/treeViewVisibilityDidChange

The visibility did change notification is sent from the client to the server to notify that the visibility of a tree view has changed.

Notification:

• method: metals/treeViewVisibilityDidChange
• params: TreeViewVisibilityDidChangeParams defined as follows:

interface TreeViewVisibilityDidChangeParams {
  /** The ID of the view that this node is associated with. */
  viewId: string;
  /** True if the node is visible in the editor UI, false otherwise. */
  visible: boolean;
}

metals/treeViewNodeCollapseDidChange

The collapse did change notification is sent from the client to the server to notify that a tree node has either been collapsed or expanded.

Notification:

• method: metals/treeViewNodeCollapseDidChange
• params: TreeViewNodeCollapseDidChangeParams defined as follows:

interface TreeViewNodeCollapseDidChangeParams {
  /** The ID of the view that this node is associated with. */
  viewId: string;
  /** The URI of the node that was collapsed or expanded. */
  nodeUri: string;
  /** True if the node is collapsed, false if the node was expanded. */
  collapsed: boolean;
}

metals/treeViewReveal

The reveal request is sent from the client to the server to convert a text document position into it's corresponding tree view node.

Request:

• method: metals/treeViewReveal
• params: TextDocumentPositionParams, as defined in LSP.

Response:

• result: TreeViewRevealResult defined as follows.

interface MetalsTreeRevealResult {
  /** The ID of the view that this node is associated with. */
  viewId: string;
  /**
   * The list of URIs for the node to reveal and all of its ancestor parents.
   *
   * The node to reveal is at index 0, it's parent is at index 1 and so forth
   * up until the root node.
   */
  uriChain: string[];
}

Example implementation of the reveal request.