Add automatic indentation-detection (experimental)

Editorconfig is given precedence. If it successfully sets an
indent_style or indent_size for the current buffer, automatic
indentation detection will be disabled.

core/core-editor.el

@@ -10,6 +10,11 @@ modes are active and the buffer is read-only.")
     doc-view-mode doc-view-mode-maybe ebrowse-tree-mode pdf-view-mode)
   "Major modes that `doom|check-large-file' will ignore.")
 
+(defvar-local doom-inhibit-indent-detection nil
+  "A buffer-local flag that indicates whether `dtrt-indent' should try to detect
+indentation settings or not. This should be set by editorconfig if it
+successfully sets indent_style/indent_size.")
+
 (setq-default
  vc-follow-symlinks t
  ;; Save clipboard contents into kill-ring before replacing them
@@ -170,6 +175,15 @@ fundamental-mode) for performance sake."
   (setq command-log-mode-auto-show t
         command-log-mode-open-log-turns-on-mode t))
 
+(def-package! dtrt-indent
+  :config
+  (setq dtrt-indent-verbosity (if doom-debug-mode 2 0))
+
+  (defun doom|detect-indentation ()
+    (unless (or doom-inhibit-indent-detection (eq major-mode 'fundamental-mode))
+      (dtrt-indent-mode +1)))
+  (add-hook 'after-change-major-mode-hook #'doom|detect-indentation))
+
 (def-package! expand-region
   :commands (er/expand-region er/contract-region er/mark-symbol er/mark-word)
   :config

core/packages.el

@@ -23,6 +23,7 @@
 (package! ace-window)
 (package! avy)
 (package! command-log-mode)
+(package! dtrt-indent)
 (package! expand-region)
 (package! helpful)
 (package! pcre2el)

modules/tools/editorconfig/config.el

@@ -39,6 +39,12 @@ extension, try to guess one."
       (apply orig-fn args)))
   (advice-add #'editorconfig-call-editorconfig-exec :around #'doom*editorconfig-smart-detection)
 
+  (defun +editorconfig|disable-indent-detection (props)
+    (when (or (gethash 'indent_style props)
+              (gethash 'indent_size props))
+      (setq doom-inhibit-indent-detection t)))
+  (add-hook 'editorconfig-custom-hooks #'+editorconfig|disable-indent-detection)
+
   ;; Editorconfig makes indentation too rigid in Lisp modes, so tell
   ;; editorconfig to ignore indentation there. I prefer dynamic indentation
   ;; support built into Emacs.