A certain line where print_width is not respected

[eproxus]

There's a bug where {print_width, 80} is not respected when formatting the following module (doesn't compile because I tried to make a minimal example):

-module(hello).

% API
-export([start/2]).

start(_Opts, Routes) ->
    App = foo,
    AllRoutes = routes(App, [{"/hello", hello_static, #{app => hello}}|Routes]).

Line 8 is exactly 80 characters wide.

Actual outcome

-module(hello).

% API
-export([start/2]).

start(_Opts, Routes) ->
    App = foo,
    AllRoutes = routes(App, [{"/hello", hello_static, #{app => hello}} | Routes]). % width = 82

Line 8 is now 82 characters wide.

Expected outcome

-module(hello).

% API
-export([start/2]).

start(_Opts, Routes) ->
    App = foo,
    AllRoutes = routes(App, [
        {"/hello", hello_static, #{app => hello}}
        | Routes
    ]).

Additional Information

If I set the width to 79 it works, but of course changes formatting elsewhere in other files.

The bug happens when running rebar3 fmt --write src/hello.erl and also via rebar3_formatter.

[awalterschulze]

Unfortunately this is a side effect of the underlying algorithm.
It tries its best to respect the print_width, but will sometimes overflow.
So this is working as expected.

Thank you for the very thorough report though and sorry for the delay in answering.

[eproxus]

Maybe this should be documented somewhere? I guess as part of the design principles?

That being said, it is easy to fix by introducing a variable or a manual line break.

[awalterschulze]

Good idea, how about #303

[eproxus]

@awalterschulze Great, thanks! 🙇