lsp-mode for dart does not guess correct project root

[bradyt]

The prompts created by lsp--find-root-interactively and lsp--suggest-project-root will quite likely try to pass a directory having a .git directory, or similar. This may frequently be incorrect, as I believe the dart_analysis_server should be passed a directory at or above a directory with pubspec.yaml (or BUILD). I suspect we can in fact pass any directory above such, in particular, the directory of current file.

This way, the prompts will be more helpful for user, and even, user can better use lsp-auto-guess-root.

The following diff helps ensure the right directory is passed to dart_language_server. (I'm making a lot of assumptions about how dart_language_server, LSP, and lsp-mode all work together.)

@@ -1266,6 +1266,11 @@ disappearing, unset all the variables related to it."
 (defun lsp--suggest-project-root ()
   "Get project root."
   (or
+   (when (eq major-mode 'dart-mode)
+     (let ((file (buffer-file-name (current-buffer))))
+       (or (locate-dominating-file file "pubspec.yaml")
+           (locate-dominating-file file "BUILD")
+           (file-name-directory file))))
    (when (featurep 'projectile) (condition-case nil
                                     (projectile-project-root)
                                   (error nil)))

My assumptions are based on the following lines from https://github.com/natebosch/dart_language_server/blob/master/lib/src/utils/package_dir_detection.dart#L19-L21, and some notes about rootUri in the changelog at same project.

bool _isPackageRoot(Directory dir) => dir.listSync().any((f) =>
    f.path.endsWith('${Platform.pathSeparator}pubspec.yaml') ||
    f.path.endsWith('${Platform.pathSeparator}BUILD'));

[bradyt]

Does lsp-mode set project root based on a response from server? If so, can we simply write the following?

@@ -1266,6 +1266,8 @@ disappearing, unset all the variables related to it."
 (defun lsp--suggest-project-root ()
   "Get project root."
   (or
+   (when (eq major-mode 'dart-mode)
+     (file-name-directory (buffer-file-name (current-buffer))))
    (when (featurep 'projectile) (condition-case nil
                                     (projectile-project-root)
                                   (error nil)))

[yyoncho]

Does lsp-mode set project root based on a response from server?

No, it doesn't. As far as I know the protocol does not provide methods for obtaining such information. As I mentioned in gitter, using current directory will not work either since for a project with multiple directories lsp-mode will start multiple language servers since the language server is associated with the root directory.

The prompts created by lsp--find-root-interactively and lsp--suggest-project-root will quite likely try to pass a directory having a .git directory, or similar. This may frequently be incorrect, as I believe the dart_analysis_server should be passed a directory at or above a directory with pubspec.yaml (or BUILD). I suspect we can in fact pass any directory above such, in particular, the directory of current file.

Since the logic related to root detection is fairly complex IMO it would be better to rely on project.el or projectile since they are specialized in project management or we are risking to reimplement all the complex logic that is present in these projects.

In order to get the behaviour you have described the following configuration option is needed:

(add-to-list 'projectile-project-root-files-bottom-up "pubspec.yaml") 

[bradyt]

Ah, nice. If I understand correctly, that works because of the order of functions in projectile-project-root-files-functions.

Then in case users don't have projectile installed, we might suggest they add the following:

(defun project-try-dart (dir)
  (cons 'dart (or (locate-dominating-file dir "pubspec.yaml")
                  dir)))
  
(add-hook 'project-find-functions #'project-try-dart)

(Ignoring for now that dart_language_server also looks for any directory with "BUILD".)

[yyoncho]

Yes. I am closing this for now and eventually, I will create FAQ entry if more people ask about configuring default root selection.

[bradyt]

Hmm, I think I also needed

(cl-defmethod project-roots ((project (head dart)))
  (list (cdr project)))

I'm not being very thorough at the moment, but to improve searchability, I believe I had an error like

Debugger entered--Lisp error: (cl-no-applicable-method project-roots...

which I'm hoping the above fixed.