erlang-formatter

Format Erlang code "to the standard": using Emacs' erlang-mode.

Used daily in CI on 2600Hz's Kazoo project à la gofmt.

Using as a rebar3 plugin

Add the plugin to your rebar config:

{plugins, [rebar3_fmt]}.

Then just call your plugin directly in an existing application:

$ rebar3 fmt

Using make

.PHONY: fmt
FMT = _build/erlang-formatter-master/fmt.sh
$(FMT):
    mkdir -p _build/
    curl -f#SL 'https://codeload.github.com/fenollp/erlang-formatter/tar.gz/master' | tar xvz -C _build/

# Pick either this one to go through the whole project
fmt: TO_FMT ?= .
# Or this faster, incremental pass
#fmt: TO_FMT ?= $(shell git --no-pager diff --name-only HEAD origin/master -- '*.app.src' '*.config' '*.config.script' '*.erl' '*.escript' '*.hrl')

fmt: $(FMT)
    $(if $(TO_FMT), $(FMT) $(TO_FMT))
# Example:
#   TO_FMT='src/a.erl include/b/hrl' make fmt

Dependencies

• emacs ≥ 24

Notes

Some alternatives (in no particular order) to this dependency-heavy utility:

• For Vim users this can help
• erl_tidy
• vim-erlang-runtime
• erlang_stdin_formatter
• erlang_string_io
• sourcer
• erl_tidy

To do

1. less verbose on no errors
2. add newline to end of file when missing
3. make it faster
4. ensure it respects file-local settings like %% -*- erlang-indent-level: 2; indent-tabs-mode: nil -*-
5. option handling to disable default TABs policy (default: spaces only)
   • Reminiscent of Just like the CAP theorem, I posit the TIA theorem: tabs, indentation, alignment, choose two. -- Loïc Hoguin
6. maybe: do not depend on Emacs

More at https://github.com/fenollp/erlang-formatter/issues

Bugs uncovered with this project

1. ERL-204: $ embedded at the end of a string causes wrong indentation
2. ERL-210: {} inside multiline strings are indented
3. ERL-212: Linebreak after fun but before ( breaks indentation
4. ERL-228: Defining type as a tuple containing a fun() followed by expression throws Emacs error
5. ERL-526: Binary in a multiline list comprehension nests wrongly

Feel free to report issues encountered with this tool. I will minify & report them.