[PATCH] D100778: [clang-format] Prevent extraneous space insertion in bitshift operators

Mon Apr 19 14:38:16 PDT 2021

penagos marked an inline comment as done.
penagos added inline comments.

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Comment at: clang/unittests/Format/FormatTest.cpp:7652

+  verifyFormat("test < a - 1 >> 1;");
   verifyFormat("test >> a >> b;");
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Quuxplusone wrote:
> Quuxplusone wrote:
> > IMO you should use `"test < a | b >> c;"` as your test case here, to reassure the reader that it doesn't depend on the fact that `... 1;` is visibly not a variable declaration.
> > Personally I'd also like to see `"test<test<a | b>> c;"` tested on the very next line, to show off the intended difference between the two. (Assuming that I understand the intent of this patch correctly.)
> > (I also switched to a bitwise operator just for the heck of it; that makes this expression just a //very tiny bit// less implausible — but still highly implausible, to the point where I question why we're special-casing it.)
> Btw, a much-bigger-scope way to fix this would be to teach clang-format about "input encoding" versus "output encoding." The only time clang-format should //ever// be inserting space in the middle of `>>` is if it's translating C++11-encoded input into C++03-encoded output. If the input is known to already be C++03-encoded, then breaking up an `>>` token into a pair of `> >` tokens is //guaranteed// to introduce a bug.
> Right now, my impression is that clang-format has a concept of "output encoding" (i.e. "language mode") but has no way of knowing the "input encoding."
Thanks for the feedback. Your 2 test suggestions make sense to me; I've updated the patch diff. I hadn't considered teaching clang-format input encoding, but that does sound like the preferable long term solution. This patch is intended to be a lightweight fix to fix a very narrow use case.

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  https://reviews.llvm.org/D100778/new/

https://reviews.llvm.org/D100778