[cfe-dev] Preprocessing and whitespace collapsing

[Anders Bakken]

Awesome. Thanks. I'll try it out.

Anders

On Tue, Jan 14, 2014 at 10:35 AM, Argyrios Kyrtzidis <akyrtzi at gmail.com> wrote:
>
> On Jan 13, 2014, at 9:46 PM, 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?
>
> Yes, with "-traditional-cpp”
>
> -Argyrios
>
>> 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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>