gptel-context: Allow exclusion of gitignored files

README.org

@@ -1005,6 +1005,7 @@ 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.">
 
+Additionally, you can exclude files or directories in git repositories listed in the =.gitignore= file by setting the user option =gptel-context-exclude-gitignored= to =t=.  This can be especially useful when adding entire projects to the context.
 *** 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

@@ -84,6 +84,13 @@ context chunk.  This is accessible as, for example:
   :group 'gptel
   :type 'function)
 
+(defcustom gptel-context-exclude-gitignored t
+  "Whether to exclude gitignored files from context.
+When non-nil, do not add to the context files or directories listed in
+the `.gitignore' file of their associated repository."
+  :group 'gptel
+  :type 'boolean)
+
 (defun gptel-context-add (&optional arg confirm)
   "Add context to gptel in a DWIM fashion.
 
@@ -127,8 +134,9 @@ context chunk.  This is accessible as, for example:
 	(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)
+	 (not (gptel-context--skip-file-p (buffer-file-name)))
+	 (buffer-file-name))
     (funcall (if (and arg (< (prefix-numeric-value arg) 0))
               #'gptel-context-remove
               #'gptel-context-add-file)
@@ -198,9 +206,19 @@ 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)))
+  (let ((files (directory-files-recursively path "." t))
+        (git-root (and gptel-context-exclude-gitignored
+                       (executable-find "git")
+                       (locate-dominating-file path ".git")))
+        unignored-files)
+    ;; Get the list of unignored files once if needed
+    (when git-root
+      (setq unignored-files (gptel-context--git-files git-root)))
     (mapc (lambda (file)
-            (unless (file-directory-p file)
+            (unless (or (file-directory-p file)
+                        (and git-root
+                             (not (member (file-relative-name file git-root)
+                                          unignored-files))))
               (pcase-exhaustive action
                 ('add
                  (if (gptel--file-binary-p file)
@@ -219,14 +237,38 @@ If PATH is a directory, recursively add all files in it.
 PATH should be readable as text."
   (interactive "fChoose file to add to context: ")
   (cond ((file-directory-p path)
-	 (gptel-context--add-directory path 'add))
-	((gptel--file-binary-p path)
+         (gptel-context--add-directory path 'add))
+        ((and gptel-context-exclude-gitignored
+              (gptel-context--skip-file-p path))
+         (message "Skipping git-ignored file: %s" 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)
 
+(defun gptel-context--git-files (dir)
+  "Return a list of unignored files in the Git repo at DIR."
+  (let ((default-directory dir))
+    (condition-case err
+        (process-lines "git" "ls-files" "--cached" "--others" "--exclude-standard")
+      (error
+       (message "Error running git ls-files in %s: %S" dir err)
+       nil))))
+
+(defun gptel-context--skip-file-p (file)
+  "Return non-nil if FILE should be skipped due to gitignore rules.
+This function assumes it will be called with a list of unignored files
+available or will make a direct Git call for a single file check."
+  (when (and gptel-context-exclude-gitignored
+             (executable-find "git"))
+    (when-let* ((git-root (locate-dominating-file file ".git"))
+                (rel-path (file-relative-name file git-root)))
+      ;; Get unignored files directly for this single file
+      (let ((unignored (gptel-context--git-files git-root)))
+        (not (member rel-path unignored))))))
+
 (defun gptel-context-remove (&optional context)
   "Remove the CONTEXT overlay from the contexts list.