This document tells you how you can contribute to fish.

Fish is free and open source software, distributed under the terms of the GPLv2.

Contributions are welcome, and there are many ways to contribute!

Whether you want to change some of the core Rust source, enhance or add a completion script or function, improve the documentation or translate something, this document will tell you how.

Fish is developed on Github, at https://github.com/fish-shell/fish-shell.

First, you'll need an account there, and you'll need a git clone of fish. Fork it on Github and then run:

git clone https://github.com/<USERNAME>/fish-shell.git

This will create a copy of the fish repository in the directory fish-shell in your current working directory.

Also, for most changes you want to run the tests and so you'd get a setup to compile fish. For that, you'll require:

• Rust - when in doubt, try rustup
• CMake
• PCRE2 (headers and libraries) - optional, this will be downloaded if missing
• gettext (headers and libraries) - optional, for translation support
• Sphinx - optional, to build the documentation

Of course not everything is required always - if you just want to contribute something to the documentation you'll just need Sphinx, and if the change is very simple and obvious you can just send it in. Use your judgement!

Once you have your changes, open a pull request on https://github.com/fish-shell/fish-shell/pulls.

In short:

• Be conservative in what you need (keep to the agreed minimum supported Rust version, limit new dependencies)
• Use automated tools to help you (including make test and build_tools/style.fish)

Completion scripts are the most common contribution to fish, and they are very welcome.

In general, we'll take all well-written completion scripts for a command that is publically available. This means no private tools or personal scripts, and we do reserve the right to reject for other reasons.

Before you try to contribute them to fish, consider if the authors of the tool you are completing want to maintain the script instead. Often that makes more sense, specifically because they can add new options to the script immediately once they add them, and don't have to maintain one completion script for multiple versions. If the authors no longer wish to maintain the script, they can of course always contact the fish maintainers to hand it over, preferably by opening a PR. This isn't a requirement - if the authors don't want to maintain it, or you simply don't want to contact them, you can contribute your script to fish.

Completion scripts should

1. Use as few dependencies as possible - try to use fish's builtins like string instead of grep and awk, use python to read json instead of jq (because it's already a soft dependency for fish's tools)
2. If it uses a common unix tool, use posix-compatible invocations - ideally it would work on GNU/Linux, macOS, the BSDs and other systems
3. Option and argument descriptions should be kept short. The shorter the description, the more likely it is that fish can use more columns.
4. Function names should start with __fish, and functions should be kept in the completion file unless they're used elsewhere.
5. Run fish_indent on your script.
6. Try not to use minor convenience features right after they are available in fish - we do try to keep completion scripts backportable. If something has a real impact on the correctness or performance, feel free to use it, but if it is just a shortcut, please leave it.

Put your completion script into share/completions/name-of-command.fish. If you have multiple commands, you need multiple files.

If you want to add tests, you probably want to add a littlecheck test. See below for details.

The documentation is stored in doc_src/, and written in ReStructured Text and built with Sphinx.

To build it locally, run from the main fish-shell directory:

sphinx-build -j 8 -b html -n doc_src/ /tmp/fish-doc/

which will build the docs as html in /tmp/fish-doc. You can open it in a browser and see that it looks okay.

The builtins and various functions shipped with fish are documented in doc_src/cmds/.

To ensure your changes conform to the style rules run

build_tools/style.fish

before committing your change. That will run our autoformatters:

• rustfmt for Rust
• fish_indent (shipped with fish) for fish script
• black for python

If you’ve already committed your changes that’s okay since it will then check the files in the most recent commit. This can be useful after you’ve merged another person’s change and want to check that it’s style is acceptable. However, in that case it will run clang-format to ensure the entire file, not just the lines modified by the commit, conform to the style.

If you want to check the style of the entire code base run

build_tools/style.fish --all

That command will refuse to restyle any files if you have uncommitted changes.

1. All fish scripts, such as those in the share/functions and tests directories, should be formatted using the fish_indent command.
2. Function names should be in all lowercase with words separated by underscores. Private functions should begin with an underscore. The first word should be fish if the function is unique to fish.
3. The first word of global variable names should generally be fish for public vars or _fish for private vars to minimize the possibility of name clashes with user defined vars.

If you use Vim: Install vim-fish, make sure you have syntax and filetype functionality in ~/.vimrc:

syntax enable
filetype plugin indent on

Then turn on some options for nicer display of fish scripts in ~/.vim/ftplugin/fish.vim:

" Set up :make to use fish for syntax checking.
compiler fish

" Set this to have long lines wrap inside comments.
setlocal textwidth=79

" Enable folding of block structures in fish.
setlocal foldmethod=expr

If you use Emacs: Install fish-mode (also available in melpa and melpa-stable) and (setq-default indent-tabs-mode nil) for it (via a hook or in use-packages “:init” block). It can also be made to run fish_indent via e.g.

(add-hook 'fish-mode-hook (lambda ()
    (add-hook 'before-save-hook 'fish_indent-before-save)))

Use cargo fmt and cargo clippy. Clippy warnings can be turned off if there's a good reason to.

The source code for fish includes a large collection of tests. If you are making any changes to fish, running these tests is a good way to make sure the behaviour remains consistent and regressions are not introduced. Even if you don’t run the tests on your machine, they will still be run via Github Actions.

You are strongly encouraged to add tests when changing the functionality of fish, especially if you are fixing a bug to help ensure there are no regressions in the future (i.e., we don’t reintroduce the bug).

The tests can be found in three places:

• src/tests for unit tests.
• tests/checks for script tests, run by littlecheck
• tests/pexpects for interactive tests using pexpect

When in doubt, the bulk of the tests should be added as a littlecheck test in tests/checks, as they are the easiest to modify and run, and much faster and more dependable than pexpect tests. The syntax is fairly self-explanatory. It's a fish script with the expected output in # CHECK: or # CHECKERR: (for stderr) comments.

The pexpects are written in python and can simulate input and output to/from a terminal, so they are needed for anything that needs actual interactivity. The runner is in build_tools/pexpect_helper.py, in case you need to modify something there.

The tests can be run on your local computer on all operating systems.

cmake path/to/fish-shell
make test

Since developers sometimes forget to run the tests, it can be helpful to use git hooks (see githooks(5)) to automate it.

One possibility is a pre-push hook script like this one:

#!/bin/sh
#### A pre-push hook for the fish-shell project
# This will run the tests when a push to master is detected, and will stop that if the tests fail
# Save this as .git/hooks/pre-push and make it executable

protected_branch='master'

# Git gives us lines like "refs/heads/frombranch SOMESHA1 refs/heads/tobranch SOMESHA1"
# We're only interested in the branches
while read from _ to _; do
    if [ "x$to" = "xrefs/heads/$protected_branch" ]; then
        isprotected=1
    fi
done
if [ "x$isprotected" = x1 ]; then
    echo "Running tests before push to master"
    make test
    RESULT=$?
    if [ $RESULT -ne 0 ]; then
        echo "Tests failed for a push to master, we can't let you do that" >&2
        exit 1
    fi
fi
exit 0

This will check if the push is to the master branch and, if it is, only allow the push if running make test succeeds. In some circumstances it may be advisable to circumvent this check with git push --no-verify, but usually that isn’t necessary.

To install the hook, place the code in a new file .git/hooks/pre-push and make it executable.

We use Coverity’s static analysis tool which offers free access to open source projects. While access to the tool itself is restricted, fish-shell organization members should know that they can login here with their GitHub account. Currently, tests are triggered upon merging the master branch into coverity_scan_master. Even if you are not a fish developer, you can keep an eye on our statistics there.

Fish uses the GNU gettext library to translate messages from English to other languages.

Creating and updating translations requires the Gettext tools, including xgettext, msgfmt and msgmerge. Translation sources are stored in the po directory, named LANG.po, where LANG is the two letter ISO 639-1 language code of the target language (eg de for German).

To create a new translation:

• generate a messages.pot file by running build_tools/fish_xgettext.fish from the source tree
• copy messages.pot to po/LANG.po

To update a translation:

• generate a messages.pot file by running build_tools/fish_xgettext.fish from the source tree
• update the existing translation by running msgmerge --update --no-fuzzy-matching po/LANG.po messages.pot

The --no-fuzzy-matching is important as we have had terrible experiences with gettext's "fuzzy" translations in the past.

Many tools are available for editing translation files, including command-line and graphical user interface programs. For simple use, you can just use your text editor.

Open up the po file, for example po/sv.po, and you'll see something like:

msgid "%ls: No suitable job\n"
msgstr ""

The msgid here is the "name" of the string to translate, typically the english string to translate. The second line (msgstr) is where your translation goes.

For example:

msgid "%ls: No suitable job\n"
msgstr "%ls: Inget passande jobb\n"

Any %s / %ls or %d are placeholders that fish will use for formatting at runtime. It is important that they match - the translated string should have the same placeholders in the same order.

Also any escaped characters, like that \n newline at the end, should be kept so the translation has the same behavior.

Our tests run msgfmt --check-format /path/to/file, so they would catch mismatched placeholders - otherwise fish would crash at runtime when the string is about to be used.

Be cautious about blindly updating an existing translation file. Trivial changes to an existing message (eg changing the punctuation) will cause existing translations to be removed, since the tools do literal string matching. Therefore, in general, you need to carefully review any recommended deletions.

All non-debug messages output for user consumption should be marked for translation. In Rust, this requires the use of the wgettext! or wgettext_fmt! macros:

streams.out.append(wgettext_fmt!("%ls: There are no jobs\n", argv[0]));

All messages in fish script must be enclosed in single or double quote characters for our message extraction script to find them. They must also be translated via a command substitution. This means that the following are not valid:

echo (_ hello)
_ "goodbye"

Above should be written like this instead:

echo (_ "hello")
echo (_ "goodbye")

You can use either single or double quotes to enclose the message to be translated. You can also optionally include spaces after the opening parentheses or before the closing parentheses.

The fish version is constructed by the build_tools/git_version_gen.sh script. For developers the version is the branch name plus the output of git describe --always --dirty. Normally the main part of the version will be the closest annotated tag. Which itself is usually the most recent release number (e.g., 2.6.0).