Emacs Tabs and Tab Groups

From other editors I am used to having Tabbars. Switching to Emacs I miss that behavior. Emacs does have a tabbar plugin, but it isn’t quite what I want.

By default it groups the tabs in a seemingly random way. I am sure it makes sense if you wrote it, but for me I want the things group by my projects. For me a project is a diretory wich has a .git directory at its root.

First I created a simple function to get the project root, or return nil.

(defun my-project-root ()
  "Return the root of the project."
  (locate-dominating-file default-directory
    ".git"))

Basically this search all parent directories until it finds one containing the .git directory. The build in function details are.

locate-dominating-file BASE FILE searches the parent directory tree from BASE until it finds FILE.

default-directory is a file local variable which is the directory of the current file.

Next I set the tabbar-buffer-groups-function to return the group name of the current file. The only requirement is that the function return a list, but it is recommended that the list only contain a single item.

(setq tabbar-buffer-groups-function
      (lambda ()
        (let ((dir (expand-file-name default-directory)))
          (cond ((member (buffer-name) '("*Completions*"
                                         "*scratch*"
                                         "*Messages*"
                                         "*Ediff Registry*"))
                 (list "#misc"))
                ;; All Magit status goes the same place
                ((string-match "^*magit" (buffer-name)) (list "#magic"))
                ((string-match "^COMMIT_EDITMSG" (buffer-name)) (list "#magic"))
                ;; All Cider windows
                ((string-match "^*nrepl-server" (buffer-name)) (list "#cider"))
                ((string-match "^*cider" (buffer-name)) (list "#cider"))
                ;; Group tabs based on project root
                ((my-project-root) (list (my-project-root)))
                ;; Use the current dir
                (t (list dir))))))

Here we capture the absolute path of the current file. Then we check a bunch of things to determine which best represents the group name. The first thing we do is group various special buffers together. Then we use the project root to group files. And if nothing else we use the file’s directory as the group name.

lambda ARG BLOCK creates an anonymous function.

let VAR BLOCK sets a variable and then calls a block. The variable is then local to that block.

cond TUPLE TUPLE... executes tuples until the first time in the tuple is true. When it finds a true tuple it executes the second item and returns it.

member ITEM LIST returns true if the first item is contained within the second list.

buffer-name returns the name of the current buffer.

list ITEM converts an item into a single item list.

string-match REGEXP STRING returns the index of the regex in the string, or nil.

my-project-root See above.

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