Simplify cape-dabbrev behavior

* Introduce new configuration cape-dabbrev-buffer-function which controls
  precisely which buffers to scan.
* Remove cape-dabbrev-min-length

2 files changed, 66 insertions, 53 deletions

diff --git a/CHANGELOG.org b/CHANGELOG.org
index 4d73995..292dd8c 100644
--- a/CHANGELOG.org
+++ b/CHANGELOG.org
@@ -2,10 +2,24 @@
 #+author: Daniel Mendler
 #+language: en
 
+* Development
+
+- Simplify ~cape-dabbrev~ configuration.
+- ~cape-dabbrev-buffer-function~: New variable to configure the buffers searched
+  by ~cape-dabbrev~.
+- ~cape-dabbrev-check-other-buffers~: Removed in favor of ~cape-dabbrev-buffer-function~.
+- ~cape-dabbrev-min-length~: Remove variable, since it leads to confusion due to
+  missing completion candidates.
+- ~cape-same-mode-buffers~: New public function, renamed from
+  ~cape--buffers-major-mode~.
+- ~cape-text-buffers~: New function.
+- ~cape-dabbrev-buffer-function~, ~cape-line-buffer-function~: Use
+  ~cape-same-mode-buffers~.
+
 * Version 2.0 (2025-03-11)
 
 - ~cape-file~: Improve handling of environment variables as part of the path,
-  e.g., $HOME.
+  e.g., ~$HOME~.
 - ~cape-company-to-capf~: Handle updated return value convention of the ~prefix~
   action of Company backends.
 
diff --git a/cape.el b/cape.el
index 3d7e7cf..4166931 100644
--- a/cape.el
+++ b/cape.el
@@ -76,36 +76,24 @@ a function returning a single or more paths."
 (defcustom cape-dict-case-replace 'case-replace
   "Preserve case of input.
 See `dabbrev-case-replace' for details."
-  :type '(choice (const :tag "off" nil)
-                 (const :tag "use `case-replace'" case-replace)
-                 (other :tag "on" t)))
+  :type '(choice (const :tag "Disable" nil)
+                 (const :tag "Use `case-replace'" case-replace)
+                 (other :tag "Enable" t)))
 
 (defcustom cape-dict-case-fold 'case-fold-search
   "Case fold search during search.
 See `dabbrev-case-fold-search' for details."
-  :type '(choice (const :tag "off" nil)
-                 (const :tag "use `case-fold-search'" case-fold-search)
-                 (other :tag "on" t)))
-
-(defcustom cape-dabbrev-min-length 4
-  "Minimum length of Dabbrev expansions.
-This setting ensures that words which are too short
-are not offered as completion candidates, such that
-auto completion does not pop up too aggressively."
-  :type 'natnum)
-
-(defcustom cape-dabbrev-check-other-buffers t
-  "Buffers to check for Dabbrev.
-
-If t, check all other buffers, subject to Dabbrev ignore rules.
-If a function, only search the buffers returned by this function.
-Any other non-nil value only checks some other buffers, as per
-`dabbrev-select-buffers-function'."
-  :type `(choice (const :tag "off" nil)
-                 (const :tag "same-mode buffers" ,#'cape--buffers-major-mode)
-                 (function :tag "function")
-                 (const :tag "some" some)
-                 (other :tag "all" t)))
+  :type '(choice (const :tag "Disable" nil)
+                 (const :tag "Use `case-fold-search'" case-fold-search)
+                 (other :tag "Enable" t)))
+
+(defcustom cape-dabbrev-buffer-function #'cape-same-mode-buffers
+  "Function which returns list of buffers.
+The buffers are scanned for completion candidates by `cape-dabbrev'."
+  :type `(choice (const :tag "Current buffer" current-buffer)
+                 (const :tag "Text buffers" ,#'cape-text-buffers)
+                 (const :tag "Buffers with same mode" ,#'cape-same-mode-buffers)
+                 (function :tag "Custom function")))
 
 (defcustom cape-file-directory nil
   "Base directory used by `cape-file."
@@ -122,12 +110,12 @@ buffers via `org-open-at-point-global'."
   "The parent directory must exist for file completion."
   :type 'boolean)
 
-(defcustom cape-line-buffer-function #'cape--buffers-major-mode
+(defcustom cape-line-buffer-function #'cape-same-mode-buffers
   "Function which returns list of buffers.
 The buffers are scanned for completion candidates by `cape-line'."
-  :type '(choice (const :tag "Current buffer" current-buffer)
-                 (const :tag "All buffers" buffer-list)
-                 (const :tag "Buffers with same major mode" cape--buffers-major-mode)
+  :type `(choice (const :tag "Current buffer" current-buffer)
+                 (const :tag "Text buffers" ,#'cape-text-buffers)
+                 (const :tag "Buffers with same mode" ,#'cape-same-mode-buffers)
                  (function :tag "Custom function")))
 
 (defcustom cape-elisp-symbol-wrapper
@@ -145,6 +133,26 @@ The buffers are scanned for completion candidates by `cape-line'."
 
 ;;;; Helpers
 
+(defun cape-same-mode-buffers ()
+  "Return buffers with same major mode as current buffer."
+  (let ((cur (current-buffer)))
+    (cons cur
+          (cl-loop for buf in (buffer-list)
+                   if (and (not (eq buf cur))
+                           (eq major-mode (buffer-local-value 'major-mode buf)))
+                   collect buf))))
+
+(defun cape-text-buffers ()
+  "Return `text-mode' and `prog-mode' buffers."
+  (let ((cur (current-buffer)))
+    (cons cur
+          (cl-loop for buf in (buffer-list)
+                   for mode = (buffer-local-value 'major-mode buf)
+                   if (and (not (eq buf cur))
+                           (or (provided-mode-derived-p mode #'text-mode)
+                               (provided-mode-derived-p mode #'prog-mode)))
+                   collect buf))))
+
 (defun cape--case-fold-p (fold)
   "Return non-nil if case folding is enabled for FOLD."
   (if (eq fold 'case-fold-search) case-fold-search fold))
@@ -551,19 +559,17 @@ If INTERACTIVE is nil the function acts like a Capf."
 (defun cape--dabbrev-list (input)
   "Find all Dabbrev expansions for INPUT."
   (cape--silent
-    (let* ((chk cape-dabbrev-check-other-buffers)
-           (funp (and (not (memq chk '(nil t some))) (functionp chk))))
-      (dlet ((dabbrev-check-other-buffers (and chk (not funp)))
-             (dabbrev-check-all-buffers (eq chk t))
-             (dabbrev-search-these-buffers-only (and funp (funcall chk))))
-        (dabbrev--reset-global-variables)
-        (cons
-         (apply-partially #'string-prefix-p input)
-         (cl-loop with min-len = (+ cape-dabbrev-min-length (length input))
-                  with ic = (cape--case-fold-p dabbrev-case-fold-search)
-                  for w in (dabbrev--find-all-expansions input ic)
-                  if (>= (length w) min-len) collect
-                  (cape--case-replace (and ic dabbrev-case-replace) input w)))))))
+    (dlet ((dabbrev-check-other-buffers nil)
+           (dabbrev-check-all-buffers nil)
+           (dabbrev-search-these-buffers-only
+            (ensure-list (funcall cape-dabbrev-buffer-function))))
+      (dabbrev--reset-global-variables)
+      (cons
+       (apply-partially #'string-prefix-p input)
+       (cl-loop
+        with ic = (cape--case-fold-p dabbrev-case-fold-search)
+        for w in (dabbrev--find-all-expansions input ic)
+        collect (cape--case-replace (and ic dabbrev-case-replace) input w))))))
 
 (defun cape--dabbrev-bounds ()
   "Return bounds of abbreviation."
@@ -594,11 +600,10 @@ If INTERACTIVE is nil the function acts like a Capf."
 If INTERACTIVE is nil the function acts like a Capf.  In case you
 observe a performance issue with auto-completion and `cape-dabbrev'
 it is strongly recommended to disable scanning in other buffers.
-See the user options `cape-dabbrev-min-length' and
-`cape-dabbrev-check-other-buffers'."
+See the user option `cape-dabbrev-buffer-function'."
   (interactive (list t))
   (if interactive
-      (cape-interactive '((cape-dabbrev-min-length 0)) #'cape-dabbrev)
+      (cape-interactive #'cape-dabbrev)
     (when-let ((bounds (cape--dabbrev-bounds)))
       `(,(car bounds) ,(cdr bounds)
         ,(completion-table-case-fold
@@ -714,12 +719,6 @@ If INTERACTIVE is nil the function acts like a Capf."
         :category 'cape-line)
   "Completion extra properties for `cape-line'.")
 
-(defun cape--buffers-major-mode ()
-  "Return buffers with same major mode as current buffer."
-  (cl-loop for buf in (buffer-list)
-           if (eq major-mode (buffer-local-value 'major-mode buf))
-           collect buf))
-
 (defun cape--line-list ()
   "Return all lines from buffer."
   (let ((ht (make-hash-table :test #'equal))