style(clang-tidy):Use hh extension for cpp header files

[bavulapati]

Clang tidy assumes the .h files as C headers.

And that makes it not find standard library files like , <intializer_list>, <string_view>, etc.,
Somehow my VSCode also recognises it as C header.

make lint
cmake --build ./build --config Debug --target clang_tidy
gmake[1]: Entering directory '/Users/balakrishna/repos/sourcemeta/core/build'
-- Enabling SIMD NEON
-- Google Benchmark version: v1.8.5, normalized to 1.8.5
-- Enabling additional flags: -DINCLUDE_DIRECTORIES=/Users/balakrishna/repos/sourcemeta/core/vendor/googlebenchmark/include
-- Performing Test HAVE_THREAD_SAFETY_ATTRIBUTES -- success
-- Performing Test HAVE_STD_REGEX -- success
-- Performing Test HAVE_GNU_POSIX_REGEX -- failed to compile
-- Performing Test HAVE_POSIX_REGEX -- success
-- Performing Test HAVE_STEADY_CLOCK -- success
-- Performing Test HAVE_PTHREAD_AFFINITY -- failed to compile
-- Configuring done (0.3s)
-- Generating done (0.3s)
-- Build files have been written to: /Users/balakrishna/repos/sourcemeta/core/build
[100%] Analyzing sources using ClangTidy
102 warnings and 1 error generated.
Error while processing /Users/balakrishna/repos/sourcemeta/core/src/core/json/include/sourcemeta/core/json.h.
/Users/balakrishna/repos/sourcemeta/core/src/core/json/include/sourcemeta/core/json.h:8:1: error: included header json_hash.h is not used directly [misc-include-cleaner,-warnings-as-errors]
    8 | #include <sourcemeta/core/json_hash.h>
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    9 | #include <sourcemeta/core/json_value.h>
/Users/balakrishna/repos/sourcemeta/core/src/core/json/include/sourcemeta/core/json.h:48:6: error: variable 'parse_json' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables,-warnings-as-errors]
   48 | auto parse_json(std::basic_istream<JSON::Char, JSON::CharTraits> &stream,
      |      ^
/Users/balakrishna/repos/sourcemeta/core/src/core/json/include/sourcemeta/core/json.h:88:6: error: variable 'parse_json' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables,-warnings-as-errors]
   88 | auto parse_json(std::basic_istream<JSON::Char, JSON::CharTraits> &stream,
      |      ^
/Users/balakrishna/repos/sourcemeta/core/src/core/json/include/sourcemeta/core/json_hash.h:4:10: error: 'cassert' file not found [clang-diagnostic-error]
    4 | #include <cassert> // assert
      |          ^~~~~~~~~
Suppressed 99 warnings (99 in non-user code).
Use -header-filter=.* to display errors from all non-system headers. Use -system-headers to display errors from system headers as well.
3 warnings treated as errors
gmake[4]: *** [CMakeFiles/clang_tidy.dir/build.make:71: CMakeFiles/clang_tidy] Error 1
gmake[3]: *** [CMakeFiles/Makefile2:825: CMakeFiles/clang_tidy.dir/all] Error 2
gmake[2]: *** [CMakeFiles/Makefile2:832: CMakeFiles/clang_tidy.dir/rule] Error 2
gmake[1]: *** [Makefile:257: clang_tidy] Error 2
gmake[1]: Leaving directory '/Users/balakrishna/repos/sourcemeta/core/build'
make: *** [lint] Error 2

[bavulapati]

@jviotti I want to know your thoughts before changing the extension of rest of the headers

[bavulapati]

Refs sourcemeta/blaze#429

[bavulapati]

picked up the extension hh since we are using cc for implementation files

[jviotti]

That's weird. .h is pretty common in C++. There must be a way to tell ClangTidy that the project is C++, and not have it look at the extension. That would be much preferred over renaming the headers to .hh