Awesome

<img src="./img/logo.svg" alt="logo"> Ctags IDE on the True Editor! (Or, a superior code reading & auto-completion tool with pluggable backends.)

What is it?

(If you are already familiar with Citre, see changelog for the news.)

Citre started out as a tool utilizing tags files (in the ctags format). Now it is a superior code reading and auto-completion tool with pluggable backend design. The built-in backends include:

A tags file (in ctags format) backend.
A GNU global backend.
An xref adapter that transforms any xref backend into Citre backend.
Eglot backend, based on the xref adapter.

The tools offered by Citre are:

completion-at-point, xref and imenu integration.
citre-jump: A completing-read UI for jumping to definition/references.
citre-peek: A powerful code reading tool that lets you go down the rabbit hole without leaving current buffer.

Let's see them in action!

completion-at-point, with the UI of company and Vertico:

Notice the rich annotations. Candidates are annotated by (kind/type@scope), so you know "it's a member of struct thread, with pid_t type", etc. This is because Ctags "tags" format records much more abundant info than the etags "TAGS" format.

Also, notice that candidates with "member" kind are put above the others because we are in a C source file, and the current symbol is after a dot. Citre guesses that you want a struct member (but completiong won't be available just after typing a dot, due to limitations of all tagging systems).
citre-jump, with completing-read UI provided by Selectrum:
citre-peek. It opens a "peek window" to show the definition of a symbol:

And there's more. Notice the code reading history at the bottom of the peek window. Do you hate having to switch between a lot of buffers while reading code? With citre-peek, you can peek a symbol in the peek window. This allows a tree-like code reading history, that you can browse and edit, without leaving current buffer!

All above screenshots were taken in a huge project (the Linux kernel), using the tags file backend, and Citre is still fast, because readtags performes binary search on the tags file.

Quick start

Installation

You can install citre from MELPA. Below are instructions to install Citre manually.

Clone this repository:

$ git clone https://github.com/universal-ctags/citre.git /path/to/citre

Add the path to your load-path in your Emacs configuration:
```
(add-to-list 'load-path "/path/to/citre")
```
Require citre and citre-config in your configuration:
```
(require 'citre)
(require 'citre-config)
```
Or, you can read citre-config.el, and write your own config.

Pick a backend

Here's a comparison of their capabilities:

Backend	Auto-completion	Find definition	Find references	Imenu
Tags	✓	✓		✓
Global	✓	✓	✓	✓
Eglot	[1]	✓[2]	✓[2]

[1]: Auto-completion is handled by eglot itself.

[2]: Eglot backend doesn't support finding definition or references of an user inputted symbol.

Pick a backend, and read its "getting started" documentation:

You don't have to use only one backend. For example, you can use tags backend for finding definitions, eglot backend for finding references with global backend as a fallback. We'll show you how this works in the configuration section later.

Below is a brief discussion of the backends. If you still don't have an idea after reading it, I would recommended tags backend as it's fast, easy to use, and fulfills most of the needs.

Global

This is based on GNU Global, another source code indexing tool. Its advantages are:

Supports finding references.
Uses a compact binary database format, and supports incremental updating.

The disadvantages are:

Not as accurate as a language server.
Supports only 5 languages. But this can be saved by using Universal Ctags & pygments as plugin parsers.
The database only contains brief information, so the UI and filtering is not as good as the tags backend.

Eglot

This is based on Eglot, a language server client now built into Emacs. Its advantages are:

Finds definition/references accurately.

Its disadvantages are:

You need to install a language server for each language you use.
For dynamic languages, sometimes it may fail to find a definition/reference.
Some language servers can be slow and heavy on CPU/memory.

Use Citre

`citre-mode`

Use citre-mode to enable completion-at-point, xref and imenu integration. If you also use company, make sure company-capf is in company-backends.

When you open a file, Citre asks the backends if they can work (like if the tags backend cound find a tags file). If any of them can work, citre-mode is automatically enabled. If you don't use citre-config, you can put this in your configuration:

(add-hook 'find-file-hook #'citre-auto-enable-citre-mode)

`citre-jump` and `citre-peek`

Other tools provided by citre, citre-jump and citre-peek, doesn't need citre-mode enabled to work. These are all citre-jump commands:

citre-jump and citre-jump-to-reference: Jump to definition or references of symbol at point.
citre-query-jump and citre-query-jump-to-reference: Jump to definition or references of a user inputted symbol. When called with a prefix argument, the identifiers in the project is used as completion for your input, if the backend supports it.

For citre-peek, see Use Citre Peek to know how to use it.

Configuration

Here's an example configuration using use-package. Be sure to tweak it to your own need.

(use-package citre
  :defer t
  :init
  ;; This is needed in `:init' block for lazy load to work.
  (require 'citre-config)
  ;; Bind your frequently used commands.  Alternatively, you can define them
  ;; in `citre-mode-map' so you can only use them when `citre-mode' is enabled.
  (global-set-key (kbd "C-x c j") 'citre-jump)
  (global-set-key (kbd "C-x c J") 'citre-jump-back)
  (global-set-key (kbd "C-x c p") 'citre-ace-peek)
  (global-set-key (kbd "C-x c u") 'citre-update-this-tags-file)
  :config
  (setq
   ;; Set these if readtags/ctags is not in your PATH.
   citre-readtags-program "/path/to/readtags"
   citre-ctags-program "/path/to/ctags"
   ;; Set these if gtags/global is not in your PATH (and you want to use the
   ;; global backend)
   citre-gtags-program "/path/to/gtags"
   citre-global-program "/path/to/global"
   ;; Set this if you use project management plugin like projectile.  It's
   ;; used for things like displaying paths relatively, see its docstring.
   citre-project-root-function #'projectile-project-root
   ;; Set this if you want to always use one location to create a tags file.
   citre-default-create-tags-file-location 'global-cache
   ;; Set this if you'd like to use ctags options generated by Citre
   ;; directly, rather than further editing them.
   citre-edit-ctags-options-manually nil
   ;; If you only want the auto enabling citre-mode behavior to work for
   ;; certain modes (like `prog-mode'), set it like this.
   citre-auto-enable-citre-mode-modes '(prog-mode)))

These user options are for customizing enabled backends:

citre-completion-backends
citre-find-definition-backends
citre-find-reference-backends
citre-tags-in-buffer-backends
citre-identifier-list-backends
citre-auto-enable-citre-mode-backends

Each is a list that's tried in turn when Citre is doing things. For example, when finding definitions, backends in citre-find-definition-backends are tried in turn until one succeeded. See their docstrings to learn more. Normally you don't need to modify them.

Documentations

Note that the user manual doesn't cover all aspects of Citre. To learn more, use M-x customize-group to see all customizable options of Citre, and M-x describe-command to know all commands of Citre.

FAQ

Q: How to use Citre over TRAMP?

A: I don't have a remote machine to test, so I can't guarantee Citre will work over TRAMP. But I've written the code with TRAMP in mind, and for now, tags and global backends seem to work over TRAMP if you've installed required executables (readtags, global) on the remote machine. If anything goes wrong, it shouldn't be hard to fix.

For eglot backend, I've not tried. I think you need to make eglot works over TRAMP, and the eglot backend will just work.
Q: Why does xref-find-reference prompts me for a symbol, rather than pick the symbol at point?

A: By default, xref-find-references always prompts you to choose an identifier from a list. You could set xref-prompt-for-identifier to nil to make it use the symbol at point instead. See its docstring for more details.
Q: What to do if Citre didn't grab the right symbol for me, e.g., I want to find the definition of foo.bar, but can only get foo or bar?

A: For tags and global backends, you can select foo.bar first (by an active region), then find its definitions.
Q: Why doesn't Citre support automatically update tags file?

A: Citre uses both line number and a search pattern to locate a tag. When the file containing the tag is edited, Citre could still locate the tag using the search pattern. Citre even tries to locate the tag when the line containing the tag itself is edited.

So, jumping to definition is still useable when the file is edited. There's no need to frequently update the tags file.

You may ask "what if I add new definitions, or modify/delete existing ones?" The truth is, if your codebase is reasonably large that you have to index them by Ctags, then small edits won't cause much trouble. You can just update the tags file when needed.
Q: Citre freezes Emacs when opening a file on Windows.
A: I'm not 100% sure about the cause, but seems some anti-virus softwares consider the way Citre communicates with external programs to be suspicious (see this report). Try adding Emacs and the program Citre uses (readtags and global) to the whitelist and see if it's solved.

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