gptel-context: Allow exclusion of gitignored files

README.org

@@ -1005,6 +1005,8 @@ You can examine the active context from the menu:
 And then browse through or remove context from the context buffer:
 #+html: <img src="https://github.com/karthink/gptel/assets/8607532/79a5ffe8-3d63-4bf7-9bf6-0457ab61bf2a" align="center" alt="Image showing gptel's context buffer.">
 
+By default, files in a version control system that are not project files will not be added to the context. To be able to add these files, set =gptel-context-restrict-to-project-files= to =nil=. Note that remote files are always included, regardless of the value of =gptel-context-restrict-to-project-files=.
+
 *** Handle "reasoning" content
 
 Some LLMs include in their response a "thinking" or "reasoning" block.  This text improves the quality of the LLM’s final output, but may not be interesting to you by itself.  You can decide how you would like this "reasoning" content to be handled by gptel by setting the user option =gptel-include-reasoning=.  You can include it in the LLM response (the default), omit it entirely, include it in the buffer but ignore it on subsequent conversation turns, or redirect it to another buffer.  As with most options, you can specify this behvaior from gptel's transient menu globally, buffer-locally or for the next request only.

gptel-context.el

@@ -30,6 +30,7 @@
 ;;; -*- lexical-binding: t -*-
 (require 'gptel)
 (require 'cl-lib)
+(require 'project)
 
 (declare-function gptel-menu "gptel-transient")
 (declare-function dired-get-marked-files "dired")
@@ -84,6 +85,16 @@ context chunk.  This is accessible as, for example:
   :group 'gptel
   :type 'function)
 
+(defcustom gptel-context-restrict-to-project-files t
+  "Whether to restrict files eligible to be added to the context to project files.
+When set to t, files in a VCS that are not project files (such as files
+listed in `.gitignore' in a Git repository) will not be added to the context."
+  :group 'gptel
+  :type 'boolean)
+
+(defvar-local gptel-context--project-files nil
+  "Cache of project files for the current directory.")
+
 (defun gptel-context-add (&optional arg confirm)
   "Add context to gptel in a DWIM fashion.
 
@@ -124,11 +135,15 @@ context chunk.  This is accessible as, for example:
 		(y-or-n-p (format "Recursively add files from %d director%s? "
 				  (length dirs)
 				  (if (= (length dirs) 1) "y" "ies"))))
+        (unless remove-p
+          (gptel-context--ensure-project-files default-directory))
 	(mapc action-fn files))))
    ;; If in an image buffer
    ((and (derived-mode-p 'image-mode)
-         (gptel--model-capable-p 'media)
-         (buffer-file-name))
+	 (gptel--model-capable-p 'media)
+	 (buffer-file-name)
+	 (not (gptel-context--skip-p (buffer-file-name))))
+    (gptel-context--ensure-project-files default-directory)
     (funcall (if (and arg (< (prefix-numeric-value arg) 0))
               #'gptel-context-remove
               #'gptel-context-add-file)
@@ -198,35 +213,89 @@ Return PATH if added, nil if ignored."
 (defun gptel-context--add-directory (path action)
   "Process all files in directory at PATH according to ACTION.
 ACTION should be either `add' or `remove'."
-  (let ((files (directory-files-recursively path "." t)))
-    (mapc (lambda (file)
-            (unless (file-directory-p file)
-              (pcase-exhaustive action
-                ('add
-                 (if (gptel--file-binary-p file)
-                     (gptel-context--add-binary-file file)
-                   (gptel-context--add-text-file file)))
-                ('remove
-                 (setf (alist-get file gptel-context--alist nil 'remove #'equal) nil)))))
-          files)
+  (let* ((root (car-safe gptel-context--project-files)))
+    (dolist (file (directory-files-recursively path "." t))
+      (unless (file-directory-p file)
+	(if (and gptel-context-restrict-to-project-files
+		 root
+		 (eq action 'add)
+		 (not (member file gptel-context--project-files)))
+	    (gptel-context--message-skipped file)
+	  (pcase-exhaustive action
+	    ('add
+	     (if (gptel--file-binary-p file)
+		 (gptel-context--add-binary-file file)
+	       (gptel-context--add-text-file file)))
+	    ('remove
+	     (setf (alist-get file gptel-context--alist nil 'remove #'equal) nil))))))
     (when (eq action 'remove)
       (message "Directory \"%s\" removed from context." path))))
 
 (defun gptel-context-add-file (path)
   "Add the file at PATH to the gptel context.
 
-If PATH is a directory, recursively add all files in it.
-PATH should be readable as text."
+If PATH is a directory, recursively add all files in it. PATH should
+be readable as text."
   (interactive "fChoose file to add to context: ")
+  (gptel-context--ensure-project-files path)
   (cond ((file-directory-p path)
-	 (gptel-context--add-directory path 'add))
+         (gptel-context--add-directory path 'add))
+        ((and gptel-context-restrict-to-project-files
+	      (not (file-remote-p path))
+              (if gptel-context--project-files
+		  (when-let ((project (project-current nil (car-safe gptel-context--project-files))))
+                    (let ((root (project-root project)))
+                      (and (file-in-directory-p path root)
+			   (not (member path gptel-context--project-files)))))
+		;; Otherwise check individually
+		(gptel-context--skip-p path)))
+	 (gptel-context--message-skipped path))
 	((gptel--file-binary-p path)
          (gptel-context--add-binary-file path))
-	((gptel-context--add-text-file path))))
+	(t (gptel-context--add-text-file path))))
 
 ;;;###autoload (autoload 'gptel-add-file "gptel-context" "Add files to gptel's context." t)
 (defalias 'gptel-add-file #'gptel-context-add-file)
 
+;;; project-related functions
+
+(defun gptel-context--ensure-project-files (path)
+  "Ensure project files are loaded for PATH if needed.
+PATH can be a file or directory.
+
+Only loads project files if `gptel-context-restrict-to-project-files' is non-nil
+and `gptel-context--project-files' is not already set."
+  (unless gptel-context--project-files
+    (when gptel-context-restrict-to-project-files
+      (setq gptel-context--project-files
+            (gptel-context--get-project-files
+             (if (and path (file-directory-p path))
+                 path
+               (file-name-directory (or path default-directory))))))))
+
+(defun gptel-context--get-project-files (dir)
+  "Return a list of files in the project DIR, or nil if no project is found."
+  (when-let ((project (project-current nil dir)))
+    (project-files project)))
+
+(defun gptel-context--skip-p (file)
+  "Return non-nil if FILE should not be added to the context."
+  (when (and gptel-context-restrict-to-project-files
+	     (not (file-remote-p file)))
+    (when-let* ((project (project-current nil file)))
+      (not (member file (gptel-context--get-project-files (project-root project)))))))
+
+(defun gptel-context--message-skipped (file)
+  "Message that FILE is skipped because it is not a project file."
+  (let* ((type (if (file-directory-p file) "directory" "file"))
+	 (reminder (format "To include this file, unset %S."
+			   'gptel-context-restrict-to-project-files)))
+    (if-let* ((project (project-current nil (car-safe gptel-context--project-files)))
+	      (rel-file (file-relative-name file (project-root project))))
+	(message "Skipping %s \"%s\" in project \"%s\". %s"
+		 type rel-file (project-name project) reminder)
+      (message "Skipping %s \"%s\". %s" type file reminder))))
+
 (defun gptel-context-remove (&optional context)
   "Remove the CONTEXT overlay from the contexts list.