[swift-dev] Using git-clang-format in the Swift compiler code base.

Andrew Trick atrick at apple.com
Thu Jan 26 14:55:08 CST 2017

> On Jan 26, 2017, at 11:38 AM, Graydon Hoare <ghoare at apple.com> wrote:
>> On Jan 26, 2017, at 2:07 AM, Andrew Trick via swift-dev <swift-dev at swift.org> wrote:
>> Before I pull in a large PR that "accidentally" reformats a bunch of code, I want to get feedback on how Swift compiler devs plan to use `clang-format`. (BTW, here's the PR https://github.com/apple/swift/pull/6922).
>> During the code review, I ran `git clang-format` as part of being a good citizen. There's only one problem with the tool. It rewraps long boolean expressions, hiding those unsightly operators at the end of lines (after all who wants to see those?).
>>       if (some_expression->with_calls() ||
>>           another_expression->with(nested_calls()) &&
>>           an_even_longer_expression->making_your_eyes->glaze_over())
>> I don't get involved in style wars, but this is not a style change, it's an objective code quality degradation. It's a demonstrably bug-prone thing to do. It's hurt me too many times in the past, and I'm not happy using a formatting tool that injects future bugs and harms code comprehension.
> It's funny you'd mention this! I often format code that way, not out of any great love of it, but from muscle-memory of living under an old coding guideline somewhere in the distant past claiming that the ugliness of trailing unfinished-binops draws the eye to them and makes the user pay attention. Doug Crockford recommends this style; but of course Don Knuth agrees with you. I don't feel strongly about them as such, but I feel ... anti-strongly, I guess? Like changing that one thing isn't worth a cross-codebase rewrite / merge collision.

I’m not sure who’s recommending what. The above style obscures operators. Does anyone disagree with that? A lot of code has been written in that way; I think because developers value aesthetics over clarity, or just don’t think about it. I care because when something doesn’t stand out, my brain fills in the gaps with whatever it expects. For me, that leads to a bunch of silly logic errors.

I need to see it this way:

      if (some_expression->with_calls()
          || another_expression->with(nested_calls())
          && an_even_longer_expression->making_your_eyes->glaze_over())

The need for parens now stands out. Sorry this isn’t a good example. Nested expressions would make it much more compelling.

That’s the coding convention we use for Swift code (at least in the stdlib). The compiler C++ code is just a hodge-podge.
If anyone actually thinks trailing operators are a good idea for our code base, I won’t argue, but I’ve never heard that argument.

BTW- I’m not interested at all in doing a mass reformatting or forcing a convention on people. I just don’t want to apply clang-format to every line of code I touch without knowing what settings to use.


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