[cfe-dev] Preprocessing and whitespace collapsing

[Matt Fowles]

Anders~

YouCompleteMe (the vim plugin) is built with a parser and completion engine
server and a client process that sits inside vim.  Not sure how far your
implementation is, but you may wish to consider sharing work it.

https://github.com/Valloric/YouCompleteMe

Matt


On Tue, Jan 14, 2014 at 12:46 AM, Anders Bakken <agbakken at gmail.com> wrote:

> Hi
>
> We're using to make an indexer daemon which can be queried from emacs
> (or other editors if so desired). In doing this we, for various
> reasons, preprocess the file first using internal APIs and then invoke
> clang_parseTranslationUnit on the preprocessed content. The code for
> this is here:
>
> https://github.com/Andersbakken/rtags/blob/multi-process/src/RTagsClang.cpp
>
> Starting at line 450.
>
> The problem we're facing is that clang seems to collapse things like this:
>
> struct A
> {
>     void               foo();
> };
>
> into this:
>
> struct A
> {
>     void foo();
> };
>
> int main()
> {
>     A a;
>     a.foo();
> }
>
> I realize the standard (at least according to GCC) permits this and
> that it of course would speed up parsing of the resulting code ever so
> slightly. My question is, is it possible to:
>
> A) Turn this behavior off with an option?
> or
> B) Someone query which lines had what amounts of space removed.
>
> I assume something can be done since if I let
> clang_parseTranslationUnit index it without preprocessing myself
> everything works as expected.
>
> From (http://gcc.gnu.org/onlinedocs/gcc-3.3/cpp/Preprocessor-Output.html)
>
> The ISO standard specifies that it is implementation defined whether a
> preprocessor preserves whitespace between tokens, or replaces it with
> e.g. a single space. In GNU CPP, whitespace between tokens is
> collapsed to become a single space, with the exception that the first
> token on a non-directive line is preceded with sufficient spaces that
> it appears in the same column in the preprocessed output that it
> appeared in the original source file. This is so the output is easy to
> read. See Differences from previous versions. CPP does not insert any
> whitespace where there was none in the original source, except where
> necessary to prevent an accidental token paste.
>
> Thanks and kudos for an awesome project.
>
> regards
>
> Anders
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