Question: I want to rewrite parts of an opensource project. This includes renaming methods. How can I do that efficiently in emacs across the whole project?

I would rather not use hacks such as search and replace in every buffer.

Answer: 
You can use `counsel-rg` followed by `C-c C-o` to get a list of all candidates in a buffer. Press `w` to edit them with `wgrep`. I recommend `iedit` for symbol renames. Press `C-c C-c` to commit.

Dependencies:

* [ripgrep](https://github.com/BurntSushi/ripgrep)
* `counsel`, `wgrep`, `iedit` are on [MELPA](https://melpa.org)
[Inspired by Dmitry's anwer](https://emacs.stackexchange.com/a/58779/2247), but searching through the entire project (not only the open buffers) and saving all the modified files in the end:

1. Run `M-x +ivy/project-search` type your regex, it will list all results (I tend to use this function a lot so I bound it to `C-x f`).
2. Now press `M-q` and it will ask you what you want to replace the matches with, type it and press enter.
3. It will now walk you through an interactive replace, you can use `y`/`n`/`!` on each, `y` to replace, `n` to skip, and `!` to replace all without asking.
4. To save all the modified buffers, run `C-x-s` and then `!` to save all of them.

Requires: [Ivy](https://github.com/abo-abo/swiper#ivy=).