Using bookmarks with eshell and docker-tramp

Emacs comes with a pretty extensible bookmarking system. As expected, you can bookmark files (including positions in the file!) in order to quickly navigate to commonly used files. I use this for my config files, personal/gdt org files, my ledger file and so on.

Thanks to the Emacs philosophy of everything being a buffer you can also bookmark a plethora of special buffers such as email buffers, elfeed entries, info pages, help pages, dired buffers and many more. Pretty much any buffer which can be reconstructed from a set of input arguments can be bookmarked.

As a bonus it all works through the same interface, by default bound to C-x r m, so you can just hit that to see if the buffer's type is supported or not.

Adding support for new buffers is also amazingly simple. All you need to do is define a function which makes a bookmark record. A bookmark record is simply an alist with arbitrary data. You can save any state there that is necessary for the recreation of the buffer. The only required key is handler which has a function as a value. This function is given the entire bookmark record and is responsible for recreating the buffer.

You then locally assign (with setq-local) this record creating function to bookmark-make-record-function which is internally used by bookmark.el when you ask it to create a record.

Recently I've been using docker (especially docker-compose) a lot and one thing that comes up fairly often during development is that you might want to execute some commands inside the container (for example when you are using the build container pattern).

What bothered me was the fact that I had to leave Emacs, jump to the terminal and fire away the commands in there. Turns out someone clever figured out a way of using TRAMP¹ to connect into docker containers. Combined with this, I can use eshell to jump into docker container and execute commands in there. Whoa!

[12:15:50]:~/$ docker ps
CONTAINER ID        IMAGE                 NAMES
e015daa0ceac        fuco1/zathura:0.3.7   focused_hugle
[12:15:52]:~/$ cd /docker:focused_hugle:/
[12:17:01]:/docker:focused_hugle:$ ls
bin   etc     lib    mnt   root  srv  usr      zathura-cb           zathura-ps
boot  girara  lib64  opt   run   sys  var      zathura-djvu
dev   home    media  proc  sbin  tmp  zathura  zathura-pdf-poppler

To tie all of this together I've written a small package eshell-bookmark² which adds bookmark support to eshell buffers. More specifically, when the bookmark is activated it tries to open an eshell in the directory where the bookmark was created. If an eshell session already exists, it just =cd=s into that directory. The entire package is less than 30 lines including docstrings. This is really the ideal of extensibility.

Thanks to docker-compose containers having predictable names, I can now bookmark each container's eshell session and quickly jump between them as necessary, all from within Emacs. No more $ docker-compose exec application ...!