`ResourcesItem` specification might be incomplete

Related to https://github.com/sbt/sbt/issues/6550 and https://github.com/sbt/sbt/pull/6552

According to the specification, the ResourcesItem contains

export interface ResourcesItem {
  target: BuildTargetIdentifier;
  /** List of resource files. */
  resources: Uri[];
}

I think this is incomplete because the build client might want to know for each resource URI if it is a file or a directory. In the case it is a file, it does not know the relative path of the file to be copied to the target directory.

@jastice Is this part already implemented in IntelliJ and how? Do you think it is worth improving this part of the spec?

As a comparison the content of a SourcesItem is:

export interface SourcesItem {
  target: BuildTargetIdentifer;
  /** The text documents or and directories that belong to this build target. */
  sources: SourceItem[];
  /** The root directories from where source files should be relativized.
   *
   * Example: ["file://Users/name/dev/metals/src/main/scala"]
   */
  roots?: Uri[];
}

export interface SourceItem {
  /** Either a text document or a directory. A directory entry must end with a forward
   * slash "/" and a directory entry implies that every nested text document within the
   * directory belongs to this source item.
   */
  uri: Uri;

  /** Type of file of the source item, such as whether it is file or directory.
   */
  kind: SourceItemKind;

  /** Indicates if this source is automatically generated by the build and is not
   * intended to be manually edited by the user. */
  generated: Boolean;
}

[adpi2]

Or we can mix the old spec with the new spec so that all the old and new clients/servers can talk to each other:

export interface ResourcesItem {
  target: BuildTargetIdentifer;

  /** The resource files or and directories that belong to this build target. */
  resourceItems: ResourceItem[]

  /** Deprecated version of the resourceItems field
  * Servers should provide it to maintain the compatibility with older clients
  * Clients should try to read resourceItems first and fallback to resources if 
  * resourceItems is not defined.
  */
  resources: Uri[];
}

[adpi2]

My understanding is that files should get added directly to the runtime classpath, without getting relativized by a directory. I’m not sure what effect that has however, I’m unable to load up a resource file that was added directly to the classpath.

Well yes that should work but it would be better if made explicit in the data structure and specification of ResourcesItem.

Also I think the client might need to know if a resource is generated or not for the same reason as a SourceItem:

/** Indicates if this source is automatically generated by the build and is not
   * intended to be manually edited by the user. */

So I think it is worth aligning the ResourceItems structure and spec with the existing SourceItems. It would look like this:

export interface ResourcesItem {
  target: BuildTargetIdentifer;
  /** The resource files or and directories that belong to this build target. */
  resources: ResourceItem[];
}

export interface ResourceItem {
  /** Either a file or a directory.
   * A directory entry must end with a forward slash "/".
   * A directory entry implies that every nested file within the
   * directory belongs to this resource item.
   */
  uri: Uri;

  /** Type of file of the source item, such as whether it is file or directory.
   */
  kind: ResourceItemKind;

  /** Indicates if this resource is automatically generated by the build and is not
   * intended to be manually edited by the user. */
  generated: Boolean;
}

export namespace ResourceItemKind {
  /** The resource item references a normal file.  */
  export const File: Int = 1;
  /** The resource item references a directory. */
  export const Directory: Int = 2;
}