Unhelpful formatting of commented binary operator expressions

[azizk]

Elixir and Erlang/OTP versions

Erlang/OTP 27 [erts-15.0] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit:ns]

Elixir 1.17.2 (compiled with Erlang/OTP 27)

Operating system

NixOS

Current behavior

When formatting code that involves multiline binary operator expressions and comments in-between, the Elixir formatter produces an unhelpful result. The following:

# Comment about expression 1
expression1 ||
  # Comment about expression 2
  expression2 ||
  # Comment about expression 3
  expression3

formats as:

# Comment about expression 1
# Comment about expression 2
# Comment about expression 3
expression1 ||
  expression2 ||
  expression3

Expected behavior

I would expect the formatter to allow placing comments between the lines, so that we can comment the specific expressions properly:

# Comment about expression 1
expression1 ||
  # Comment about expression 2
  expression2 ||
  # Comment about expression 3
  expression3

[josevalim]

Correct, the formatter cannot preserve code comments in all situations. Some of them were already documented but this particular one was not. I have pushed updates to the documentation.

Unfortunately tackling this is non-trivial. If someone wants to give it a try, pull requests are welcome, but it is not something we intend to pursue ourselves. Thanks!

[azizk]

Okay, thanks for the explanation and update to the docs. 👍

If someone is curious how to work around this, you'd basically have to break up the expressions and use a result variable:

# Comment about expression 1
result = expression1
# Comment about expression 2
result = result || expression2
# Comment about expression 3
result = result || expression3

[josevalim]

You can also break the expressions into private functions, if they are complex enough to warrant for comments. With the advantage that the function names can also provide meaningful context.