Add support for DAP and lsp-treeview in scala layer

This is squash commit including below commits:

* Add support for DAP and lsp-treeview in scala layer
* Address notes from code review.

CHANGELOG.develop

@@ -3020,6 +3020,7 @@ Other:
 - Added scala-lsp and metals as an additional backend for scala
   (thanks to Rodolfo Hansen)
 - Disabled =sbt-supershell= in =sbt-mode= (thanks to Rodolfo Hansen)
+- Enable new DAP and lsp-treemacs integration via metals (thanks to Rodolfo Hansen)
 **** Scheme
 - Added missing =parinfer= package declaration (thanks to Kalle Lindqvist)
 - Update install docs for Chicken 5 changes (thanks to Grant Shangreaux)

layers/+lang/scala/README.org

@@ -17,9 +17,11 @@
     - [[#usage][Usage]]
 - [[#scalastyle][Scalastyle]]
   - [[#use-java-doc-style][Use Java doc-style]]
+- [[#enable-debug-adapter-protocol-dap][Enable Debug Adapter Protocol (DAP)]]
 - [[#automatically-show-the-type-of-the-symbol-under-the-cursor][Automatically show the type of the symbol under the cursor]]
 - [[#automatically-insert-asterisk-in-multiline-comments][Automatically insert asterisk in multiline comments]]
 - [[#automatically-replace-arrows-with-unicode-ones][Automatically replace arrows with unicode ones]]
+- [[#enable-gtags-as-a-fallback-navigation-utility][Enable GTags as a fallback navigation utility]]
 - [[#auto-start][Auto-start]]
 - [[#key-bindings][Key bindings]]
   - [[#ensime][Ensime]]
@@ -43,13 +45,16 @@ This layer adds support for the Scala language to Spacemacs.
 ** Features:
 - Syntax highlighting
 - Support for language backend. Either using [[https://ensime.github.io/][ENSIME]] or [[https://scalameta.org/metals/][Metals]]
+- Debugging support via dap
 - Auto-completion
+- Treeview support for viewing project structure and triggering compilation
 - Syntax-checking
 - Refactoring
 - Incremental compilation
 - Scala Repl
 - Style linting
 - Eldoc integration
+- Optional GGTags search
 - Test execution directly from Emacs
 - Automatic replacement of ASCII arrows with unicode ones
 
@@ -174,6 +179,9 @@ To enable =java-doc-style=, set the variable =scala-indent:use-javadoc-style= to
     (scala :variables scala-indent:use-javadoc-style t)))
 #+END_SRC
 
+* Enable Debug Adapter Protocol (DAP)
+The metals backend enables integration with the DAP layer for debugging support.
+
 * Automatically show the type of the symbol under the cursor
 To enable the feature =ensime-type-at-point= when cursor moves, set the
 variable =scala-enable-eldoc= to =t=.
@@ -207,6 +215,16 @@ the ascii arrows back.
     (scala :variables scala-use-unicode-arrows t)))
 #+END_SRC
 
+* Enable GTags as a fallback navigation utility
+To enable gtags when in scala-mode, in case metals, or, ensime are not fully
+functioning set the variable =scala-enable-gtags= to =t=.
+
+#+BEGIN_SRC emacs-lisp
+  (setq-default dotspacemacs-configuration-layers '(
+    (scala :variables scala-enable-gtags t)))
+#+END_SRC
+
+
 * Auto-start
 If you prefer to have the backend start when you load a scala file, you can enable it
 with

layers/+lang/scala/config.el

@@ -14,6 +14,9 @@
 (defvar scala-enable-eldoc nil
   "If non nil then eldoc-mode is enabled in the scala layer.")
 
+(defvar scala-enable-gtags nil
+  "If non nil then gtags is enabled in the scala layer.")
+
 (defvar scala-auto-insert-asterisk-in-comments nil
   "If non-nil automatically insert leading asterisk in multi-line comments.")
 

layers/+lang/scala/funcs.el

@@ -54,6 +54,16 @@
   "Setup LSP metals for Scala."
   (add-hook 'scala-mode-hook #'lsp))
 
+(defun spacemacs//scala-setup-dap ()
+  "Setup DAP in metals for Scala."
+  (when (spacemacs//scala-backend-metals-p)
+    (add-hook 'scala-mode-hook #'dap-mode)))
+
+(defun spacemacs//scala-setup-treeview ()
+  "Setup lsp-treemacs for Scala."
+  (lsp-metals-treeview-enable t)
+  (setq lsp-metals-treeview-show-when-views-received t))
+
 (defun spacemacs//scala-disable-flycheck-scala ()
   (push 'scala flycheck-disabled-checkers))
 

layers/+lang/scala/layers.el

@@ -13,4 +13,4 @@
 
 (when (and (boundp 'scala-backend)
            (eq scala-backend 'scala-metals))
-  (configuration-layer/declare-layer-dependencies '(lsp)))
+  (configuration-layer/declare-layer-dependencies '(dap)))

layers/+lang/scala/packages.el

@@ -11,14 +11,18 @@
 
 (setq scala-packages
       '(
-        (ensime :toggle (spacemacs//scala-backend-ensime-p))
         lsp-mode
-        ggtags
+        dap-mode
+        eldoc
+        flycheck
+        flyspell
+        lsp-treemacs
         counsel-gtags
+        ggtags
         helm-gtags
-        noflet
-        scala-mode
+        (ensime :toggle (spacemacs//scala-backend-ensime-p))
         sbt-mode
+        scala-mode
         ))
 
 (defun scala/post-init-eldoc ()
@@ -161,18 +165,15 @@
   (spacemacs/enable-flycheck 'scala-mode)
   ;; Don't use scala checker if ensime mode is active, since it provides
   ;; better error checking.
-  (when spacemacs//scala-backend-ensime-p
+  (when (spacemacs//scala-backend-ensime-p)
     (with-eval-after-load 'flycheck
       (add-hook 'ensime-mode-hook 'spacemacs//scala-disable-flycheck-scala))))
 
 (defun scala/post-init-flyspell ()
   (spell-checking/add-flyspell-hook 'scala-mode)
-  (when spacemacs//scala-backend-ensime-p
+  (when (spacemacs//scala-backend-ensime-p)
     (add-hook 'scala-mode-hook #'spacemacs//scala-setup-ensime-flyspell)))
 
-(defun scala/init-noflet ()
-  (use-package noflet))
-
 (defun scala/init-sbt-mode ()
   (use-package sbt-mode
     :defer t
@@ -268,15 +269,26 @@ If it's part of a left arrow (`<-'),replace it with the unicode arrow."
             scala-indent:default-run-on-strategy
             scala-indent:operator-strategy))))
 
+(defun scala/pre-init-dap-mode ()
+  (add-to-list 'spacemacs--dap-supported-modes 'scala-mode)
+  (spacemacs//scala-setup-dap))
+
 (defun scala/post-init-lsp-mode ()
   (when (spacemacs//scala-backend-metals-p)
     (spacemacs//scala-setup-metals)))
 
+(defun scala/post-init-lsp-treemacs ()
+  (when (spacemacs//scala-backend-metals-p)
+    (spacemacs//scala-setup-treeview)))
+
 (defun scala/post-init-ggtags ()
-  (add-hook 'scala-mode-local-vars-hook #'spacemacs/ggtags-mode-enable))
+  (when scala-enable-gtags
+    (add-hook 'scala-mode-local-vars-hook #'spacemacs/ggtags-mode-enable)))
 
 (defun scala/post-init-counsel-gtags ()
-  (spacemacs/counsel-gtags-define-keys-for-mode 'scala-mode))
+  (when scala-enable-gtags
+    (spacemacs/counsel-gtags-define-keys-for-mode 'scala-mode)))
 
 (defun scala/post-init-helm-gtags ()
-  (spacemacs/helm-gtags-define-keys-for-mode 'scala-mode))
+  (when scala-enable-gtags
+    (spacemacs/helm-gtags-define-keys-for-mode 'scala-mode)))