[cfe-users] [run-clang-tidy] new replacement overlaps with an existing replacement

[Jonas Toth via cfe-users]

Hi Mateusz,

comments inline.

Am 10.12.18 um 22:14 schrieb Mateusz Loskot via cfe-users:
> Hi,
>
> I'm running clang-tidy 7.0 (also tried 5.0) to modernise some aspects
> of Boost.GIL (https://github.com/boostorg/gil) source code.
>
> I've noticed, clang-tidy 7.0 (also 5.0) does not apply fixes for some of
> modernize-use-* checks, especially modernize-use-using.
>
> I run it this way:
>
> ```
> cd ${BOOST_ROOT}/libs/gil
> cmake -S . -B _build -DCMAKE_EXPORT_COMPILE_COMMANDS=ON ..
> run-clang-tidy.py -p=_build -header-filter='boost\/gil\/.*'
> -checks='-*,modernize-use-using' -fix
> ```
>
> Then, I see huge number of "The new replacement overlaps with an
> existing replacement." diagnostics.
> Below, I copied an extract that hopefully is useful to figure out what
> is happening and going wrong.
>
> Basically, there are two class templates and a bunch of tag types:
>
> 1. file_stream_device
> https://github.com/boostorg/gil/blob/e0288ece9ec50534e7d02166863d6799a5932e25/include/boost/gil/io/device.hpp#L49
> 2. get_write_device with partial specialisations, `enable_if`-ed
> https://github.com/boostorg/gil/blob/e0288ece9ec50534e7d02166863d6799a5932e25/include/boost/gil/io/get_write_device.hpp#L19-L59
>
> The file_stream_device is specialised for a tag and final
> get_write_device specialisation is matched.
>
> And, clang-tidy tries to substitute this alias in get_write_device
>
> typedef detail::file_stream_device< FormatTag > type;
>
> not with
>
> using type = detail::file_stream_device< FormatTag > ;
>
> but with `using type` for each FormatTag-based specialisation
>
> ```
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<bmp_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<bmp_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<jpeg_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<png_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<png_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<png_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<pnm_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<targa_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<targa_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<tiff_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> New replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<tiff_tag>"
> Existing replacement:
> /mnt/d/boost.wsl/libs/gil/include/boost/gil/io/get_write_device.hpp:
> 1885:+52:"using type = detail::file_stream_device<FormatTag>"
> The new replacement overlaps with an existing replacement.
> ```
>
> Why clang-tidy tries to re-fix the typedef with new replacement
> instead of keeping the existing one, the generic one?
Maybe a bug that does not handle some possible cases well. I know, that
`use-using` has its problems sometimes.
> i.e. using type = detail::file_stream_device<FormatTag>
>
> I've tried to prepare a minimal example, but I couldn't reproduce this issue.
Do you know which `TU` triggered the behaviour? If you find it out you
can fully preprocess the file and check if the behaviour is still
present. Then you can `creduce` the issue or create a bug-report and we
reduce it
> I observed, that if I manually prepare compile_database.json with
> single .cpp file that just `#include <boost/gil/io/device.hpp>`,
> that is the header with definition of the base templates
> and no definitions with higher level specialisations for format tags
> are included,
> then clang-tidy applies the expected fixes without any warnings.
>
> Could anyone share any insights about this issue?

What can happen (especially template-heavy code) that multiple
inclusions of a file (as always happening) results in different fixes
for the same code-location.

`run-clang-tidy` does the replacements at the end. That means if
multiple TUs will result in different fixes there will be collisions and
it is not resolveable which one is correct.


Best, Jonas