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From Noah Slater <nsla...@apache.org>
Subject Re: [DISCUSS] Erlang whitespace standards (was: [POLL])
Date Tue, 08 Apr 2014 10:09:38 GMT
A good next step would be for someone to move the pertinent info out
of this thread and onto the Confluence wiki.

One thing we could do is work this guide/standards into our code/PR
review procedure. i.e. We make it legit, nay expected, that people
assess patches according to the standards, in addition to the normal
review process.

On 4 April 2014 23:08, Paul Davis <paul.joseph.davis@gmail.com> wrote:
> I definitely agree we should re-format the whole code base any time
> soon. Though at some point it'd be a good idea. Hopefully we can find
> a lull after the two big forks are merged where we can just have a
> commit on each Erlang repo to do the deed while there's no large
> outstanding work that'd be super difficult to merge.
>
> On Fri, Apr 4, 2014 at 9:33 AM, Robert Samuel Newson <rnewson@apache.org> wrote:
>> I appreciate firming up a consensus on indentation styles but I want to be clearly
-1 on a codebase-wide reformatting for the foreseeable future. Beyond the merges, we have
active branches for older releases, the more reformatting we do, the harder back- and forward-porting
becomes. I like the idea of being more consistent for future work and, where code is particularly
crufty, refactoring before making a change. The "worst" formatted code in couchdb is generally
the oldest, and much of that needs a refactor/rewrite as we get to it.
>>
>> B.
>>
>> On 4 Apr 2014, at 14:07, Alexander Shorin <kxepal@gmail.com> wrote:
>>
>>> Hi Joan and all,
>>>
>>> I just faced another indention case which left out of scope of the vote:
>>> https://gist.github.com/kxepal/2c09fb5348ead90bea04
>>>
>>> Personally, I'm for 1) variant there.
>>>
>>> Another interesting case is anonymous function:
>>> https://gist.github.com/kxepal/c5480209af9e93a14155
>>>
>>> I prefer 3) one.
>>>
>>> What would be your recommendations there about?
>>>
>>> --
>>> ,,,^..^,,,
>>>
>>>
>>> On Fri, Apr 4, 2014 at 9:24 AM, Joan Touzet <joant@atypical.net> wrote:
>>>> Hi everyone,
>>>>
>>>> Time to summarize the results. You can view the results at
>>>>
>>>> https://docs.google.com/forms/d/1b7KcQGgNbSCZVRwLjrUl5Z6C2TBx8X1btlU5fwrNHpg/viewanalytics
>>>>
>>>> but I've included them in this email for ease of review.
>>>>
>>>> I'm going to break this up into sections and make some PROPOSALs.  I'd
>>>> like to get general consensus on this vs. a "lazy" approach.  I don't
>>>> see this as something where need a unanimous vote but I'd like to get us
>>>> all agree on something we can live with.
>>>>
>>>> As for getting this into the code base - let's not endanger the big
>>>> merges, but once we have finished them, we should move to these
>>>> standards piecemeal as we rework each file, as Noah and Jan suggest,
>>>> unless someone wants to do the busy work and re-indent everything.
>>>> Hopefully, even with the wait for the merges, this means the standard
>>>> can be "live" before the end of 2014 ;)
>>>>
>>>> I don't cover all topics in here - please feel free to follow the post's
>>>> format and add additional proposals in follow-ups.
>>>>
>>>> Finally, if I say something you disagree with or if I have misinterpreted
>>>> your response, speak up - it was not intentional!
>>>>
>>>> -Joan
>>>>
>>>> -----
>>>>
>>>> TERMINOLOGY USED:
>>>>  * "X space indent" means X spaces from the LEFT MARGIN.
>>>>    It is the ABSOLUTE number of columns of whitespace on a line.
>>>>
>>>>  * "Y space standard" means indentations should be multiples
>>>>    of Y spaces.
>>>>
>>>>  * "Z level indent" means Z*Y=X absolute spaces for the indent.
>>>>    For a 4-space standard, a 2 level indent would mean an 8 space
>>>>    indent.
>>>>
>>>> -----
>>>>
>>>> STANDARD: Agree on a 4-space standard for horiz. indentation. Most of
>>>> the respondents seem to be comfortable with this, likely due to the
>>>> prevalence of the Python / Ruby / JS 4-space standard.
>>>>
>>>> PROPOSAL: "Indent your code blocks with 4 spaces. Never use tabs or a
>>>> mix of tabs and spaces. When additional indentation levels are needed,
>>>> always increment by a multiple of 4 spaces."
>>>>
>>>> This sets us up to be able to have the same spacing standard across JS,
>>>> C and other languages we may someday ship.
>>>>
>>>> -----
>>>>
>>>> LINE LENGTH: 11 votes for 80, 6 votes for 132, 1 for 76.
>>>>
>>>> PROPOSAL: "Maximum line length is 80 characters, with a preference for
>>>> 76 characters or less.  Exception: URLs in comments"
>>>>
>>>> -----
>>>>
>>>> CASE STATEMENT INDENTATION: 16 in favour of this format, 3 opposed:
>>>>
>>>> get_ini_files(Default) ->
>>>>    case init:get_argument(couch_ini) of
>>>>        error ->
>>>>            Default;
>>>>        {ok, [[]]} ->
>>>>            Default;
>>>>        {ok, [Values]} ->
>>>>            Values
>>>>    end.
>>>>
>>>> This format matches Erlang documentation and is fairly canonical.
>>>>
>>>> PROPOSAL: "Indent case pattern clauses 1 level, and each case pattern
>>>> body 2 levels from the initial case statement."
>>>>
>>>> -----
>>>>
>>>> CASE STATEMENT ONE-LINERS: 11 in favour, 8 opposed:
>>>>
>>>>    case {Name, Pass} of
>>>>        {"Jan Lehnardt", "apple"} -> ok;
>>>>        ...
>>>>
>>>> The only write-in for this suggested that one-liners needed to fit on a
>>>> single line "without looking terrible."
>>>>
>>>> PROPOSAL: "Generally, case pattern bodies should always start on a new
>>>> line from their corresponding case pattern clause. However, you can put
>>>> the clause and body on the same line if the entire statement fits on one
>>>> line."
>>>>
>>>> This is a tough one because it directly contradicts the previous
>>>> proposal. If people feel strongly I am OK to be more strict and remove
>>>> "Generally, " and the second sentence from this proposal.
>>>>
>>>> -----
>>>>
>>>> LONG FUNCTION CLAUSE:
>>>>
>>>> 7 for paren aligned
>>>> 4 for 2-space indented
>>>> 5 for 8-space indented
>>>> 1 for "2 space, but no arguments on the initial line, with
>>>>       the closing } on its own line"
>>>> 1 for "4-space indented"
>>>> 1 for "one tab"
>>>>
>>>> As a reminder, here is the code, paren aligned:
>>>>
>>>> possibly_embed_doc(#collector{db_name=DbName, query_args=Args),
>>>>                   #view_row{key=_Key, id=_Id, value=Value, doc=_Doc}=Row)
->
>>>>
>>>> And 8-space aligned:
>>>>
>>>> possibly_embed_doc(
>>>>        #collector{db_name=DbName, query_args=Args),
>>>>        #view_row{key=_Key, id=_Id, value=Value, doc=_Doc}=Row) ->
>>>>
>>>>
>>>> Ideology here and on the list is split roughly into 2 camps:
>>>>
>>>>  * Z-level indent of a multiple of 4 spaces. As the body of the
>>>>    function will start at 4 spaces, I am going to recommend
>>>>    against 1-level and say a 2-level (8 space) indent is the
>>>>    option here.
>>>>
>>>>  * Emacs/paren indentation mode. I believe the big arguments for
>>>>    this mode is "it's what my editor does" and "it's common in
>>>>    strongly typed languages." If you feel differently, please
>>>>    speak up. On the other side, Paul feels strongly about not
>>>>    adopting this model; Wendall supports it and Bob N. says he
>>>>    can 'retrain himself' to use it. Notice also that, in this
>>>>    example, the second line ends on col. 78. Even if the -> was
>>>>    wrapped to the next line, the line still ends on col. 75.
>>>>
>>>> Tough call here. Based on similarity with other popular languages of our
>>>> day I'm going to initially propose the first option and let anyone who
>>>> strongly opposes speak up now. There was no strong statement
>>>> about whether the ) or -> should be on its own line, so I'll leave
>>>> that part of the proposal vague for now.
>>>>
>>>> PROPOSAL: "Function definitions should align wrapped elements using a
>>>> 2-level hanging indent. There should be no arguments on the first line.
>>>> The closing parenthesis or arrow may be placed on its own line if
>>>> desired, but if so, it should be indented the same number of spaces as
>>>> the function definition itself."  **but see below**
>>>>
>>>> -----
>>>>
>>>> LONG FUNCTION CALL:
>>>>
>>>> 7 for paren-aligned
>>>> 7 for 4-space indent
>>>> 3 for 8-space indent
>>>> 1 for "rework the code, or 4-space indent"
>>>> 1 for "2 space, but no arguments on the initial line, with
>>>>       the closing } on its own line"
>>>>
>>>> As a reminder, here is the code, paren-aligned:
>>>>
>>>>            [_A, _B, _Cs] = re:split(?b2l(AuthSession), ":",
>>>>                                     [{return, list}, {parts, 3}]),
>>>>
>>>> And 8-space aligned:
>>>>
>>>>            [_A, _B, _Cs] = re:split(?b2l(AuthSession), ":",
>>>>                    [{return, list}, {parts, 3}]),
>>>>
>>>> The more I looked at this topic, the more it looked like the last one,
>>>> but even more space constrained because of the existing indent of the
>>>> call itself. As such I'm going to roll it into the previous proposal:
>>>>
>>>> REVISED PROPOSAL: "Function definitions *and calls* should align wrapped
>>>> elements using a 2-level hanging indent. There should be no arguments on
>>>> the first line. The closing parenthesis or arrow may be placed on its
>>>> own line if desired, but if so, it should be indented the same number of
>>>> spaces as the function definition or call itself."
>>>>
>>>> That means these would be acceptable:
>>>>
>>>>            [_A, _B, _Cs] = re:split(?b2l(AuthSession), ":",
>>>>                    [{return, list}, {parts, 3}]),
>>>>
>>>>            [_A, _B, _Cs] = re:split(?b2l(AuthSession), ":",
>>>>                    [{return, list}, {parts, 3}]
>>>>            ),
>>>>
>>>> -----
>>>>
>>>> LONG LIST WRAPPING:
>>>>
>>>> 4 for 8-space indent
>>>> 3 for "aligned with nested structure in previous line"
>>>> 5 for "single character indent"
>>>> 9 for "indented to match correct nesting block"
>>>> 3 for "4-space indent"
>>>> 1 for "2 with indented case"
>>>>
>>>> Reminder: You could vote for multiple options for this question.
>>>>
>>>> Here is the code block formatted with single-character indent:
>>>>
>>>>    case lists:member(revs, Options) of
>>>>        false ->
>>>>            [];
>>>>        true ->
>>>>            [{<<"revisions">>, {[{<<"start">>, Start},
>>>>             {<<"ids">>, [revid_to_str(R) ||R ,_ RevIds]}]}}]
>>>>    end.
>>>>
>>>> And indented to match correct nesting block:
>>>>
>>>>    case lists:member(revs, Options) of
>>>>        false ->
>>>>            [];
>>>>        true ->
>>>>            [
>>>>             {<<"revisions">>,
>>>>              {[{<<"start">>, Start},
>>>>                {<<"ids">>, [revid_to_str(R) ||R ,_ RevIds]}
>>>>               ]}
>>>>             }
>>>>            ]
>>>>    end.
>>>>
>>>> This was intended to be a question to which there really was no good
>>>> answer. ;) As expected, results are across the board, except for
>>>> "indented to match correct nesting block," which appears to be popular
>>>> because it was probably the only layout one could glance at and have a
>>>> hope of understanding.
>>>>
>>>> I don't think there is a good proposal to be made here. It is a judgment
>>>> call, and I think any of "4-space indent," "8-space indent" or "indented
>>>> to match correct nesting blocks" can be made to work.
>>>>
>>>> -----
>>>>
>>>> LIST COMPREHENSION WRAP:
>>>>
>>>> 9 for "lined up for first term until || is reached
>>>> 3 for "indented 4 spaces from {ok above"
>>>> 2 for "everything indented 8 spaces"
>>>> 1 for "4 spaces from expression start, e.g. after Docs"
>>>> 1 for "Don't use multi-line list comprehensions! 4-space indent"
>>>> 1 for "no idea" :D
>>>>
>>>> Code for "lined up for first term until || is reached":
>>>>
>>>>            Docs = [Doc || {ok, Doc} <- [
>>>>                    couch_db:open_doc(Db2, DocInfo2, [deleted, conflicts])
>>>>                        || Docinfo2 <- DocInfos]],
>>>>
>>>> This was also a very ugly example that I found in our code that I wanted
>>>> to use to highlight how difficult it can be to come up with a standard.
>>>> The good news is that most people were in the 4- or 8-space camp, i.e.
>>>> 1 or 2 level indents, and that perhaps the code needs refactoring. In
>>>> the case of refactoring, I definitely agree with Bob: PRs with refactors
>>>> should not be combined with PRs for whitespace, or at the very least
>>>> should be 2 separate checkins within the same PR.
>>>>
>>>> There is no unique proposal for this other than to reference the initial
>>>> proposal in this post: "Indent your code blocks with 4 spaces. Never use
>>>> tabs or a mix of tabs and spaces. When additional indentation levels are
>>>> needed, always increment by a multiple of 4 spaces."
>>>>
>>>> -----
>>>>
>>>> VERTICAL SPACING:
>>>>
>>>> There was no poll question on this but it was brought up a few times on
>>>> the list. Going from code and proposals, there are 2 options:
>>>>
>>>> 0 blank lines between function declarations differing only in guards
>>>> 1 blank line between different function declarations, imports, etc.
>>>>
>>>> and
>>>>
>>>> 1 blank line between function declarations differing only in guards
>>>> 2 blank lines between different function declarations, imports, etc.
>>>>
>>>> I can see arguments for both. By inspection most of our code follows
>>>> the 0/1 approach, not the 1/2 approach favoured by Paul.
>>>>
>>>> -----
>>



-- 
Noah Slater
https://twitter.com/nslater

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