CMake boost super-build fixups for cmake-3.8

[nigels-com]

I've been on a little bit of an adventure to see what version of cmake is required for building boost.
See boostorg/boost#1081

Json needs cmake-3.15.0, otherwise it errors with:

-- Configuring done
CMake Error at libs/json/test/CMakeLists.txt:63 (target_compile_options):
  Error evaluating generator expression:

    $<CXX_COMPILER_ID:GNU,Clang,AppleClang>

  $<CXX_COMPILER_ID> expression requires one or zero parameters.

[cppalliance-bot]

An automated preview of the documentation is available at https://1106.json.prtest2.cppalliance.org/libs/json/doc/html/index.html

[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1106/pullrequest.html

[Flamefire]

I can confirm this change is sound: https://cmake.org/cmake/help/latest/manual/cmake-generator-expressions.7.html#genex:CXX_COMPILER_ID

Changed in version 3.15: Multiple compiler_ids can be specified. CMake 3.14 and earlier only accepted a single compiler ID.

[grisumbras]

To be honest, If that's all, I'm more willing to replace that one line with 3. I can do it myself, but if you want you can change the PR.

[nigels-com]

I've updated the change here to support cmake-3.14 (instead of cmake-3.15).

However cmake-3.13 cmake fails with -DBUILD_TESTING=Y due to parser requiring cmake-3.14:

$ PATH=/opt/cmake-3.13.0-Linux-x86_64/bin:$PATH cmake .. -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_COMPILER_LAUNCHER=ccache -DBUILD_TESTING=Y -DCMAKE_CXX_COMPILER=clang++-18 -DBUILD_TESTING=Y -DBOOST_INCLUDE_LIBRARIES=json && ninja -v
-- Boost: using system layout: include, bin, lib, lib/cmake
-- Boost: Release build, static libraries, MPI OFF, Python OFF, testing Y
-- Boost: libraries included: json
-- Boost.Charconv: quadmath support OFF
-- Boost.Context: architecture x86_64, binary format elf, ABI sysv, assembler gas, suffix .S, implementation fcontext
-- Boost.Fiber: NUMA target OS is linux
-- Boost.Iostreams: ZLIB ON, BZip2 ON, LZMA ON (multithreaded), Zstd ON
-- Found the following ICU libraries:
--   data (required)
--   i18n (required)
--   uc (required)
-- Found ICU: /usr/include (found suitable version "74.2", minimum required is "4.8.1") 
-- Boost.Locale: iconv ON, ICU ON, POSIX ON, std ON, winapi OFF
-- Boost.Math: standalone mode OFF
-- Boost.Multiprecision: standalone mode OFF
CMake Error at libs/parser/CMakeLists.txt:9 (cmake_minimum_required):
  CMake 3.14 or higher is required.  You are running version 3.13.0


-- Configuring incomplete, errors occurred!

[cppalliance-bot]

An automated preview of the documentation is available at https://1106.json.prtest2.cppalliance.org/libs/json/doc/html/index.html

[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1106/pullrequest.html

[Flamefire]

I've updated the change here to support cmake-3.14 (instead of cmake-3.15).

Why? It doesn't really matter what dependencies require. They state their requirements on their own, it is not the responsibly of this library.

How does it get pulled in though? I don't see it as a dependency. Try -DBoost_DEBUG=ON for more info

[grisumbras]

JSON definitely does not depend on Parser.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.71%. Comparing base (e280e70) to head (fa1223a).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1106   +/-   ##
========================================
  Coverage    93.71%   93.71%           
========================================
  Files           91       91           
  Lines         9156     9156           
========================================
  Hits          8581     8581           
  Misses         575      575           

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[nigels-com]

The superproject cmake does seem to pulling in Parser via a GLOB in BoostRoot.cmake.

cmake-3.13 does succeed with -DBOOST_EXCLUDE_LIBRARIES=parser specified to skip parser specifically.

[Flamefire]

The superproject cmake does seem to pulling in Parser via a GLOB in BoostRoot.cmake.

cmake-3.13 does succeed with -DBOOST_EXCLUDE_LIBRARIES=parser specified to skip parser specifically.

That glob is only for detecting available libraries. Libraries are only configured as requested. One exception is if BUILD_TESTING is set which adds all libraries but doesn't build them by default:
https://github.com/boostorg/cmake/blob/81b08178c629b94b67e3baff5b1b9bee25db7f3a/include/BoostRoot.cmake#L355-L378

[grisumbras]

https://drone.cpp.al/boostorg/json/1913/22/2

This job invokes cmake -DBoost_VERBOSE=1 -DBUILD_TESTING=ON -DCMAKE_INSTALL_PREFIX=iprefix -DBOOST_INCLUDE_LIBRARIES=json .., which results in the following (abriged) output:

...
-- Boost: using system layout: include, bin, lib, lib/cmake
-- Boost: using CMake 3.18.4
-- Boost: Release build, static libraries, MPI OFF, Python OFF, testing ON
-- Boost: libraries included: json
-- Adding Boost dependency align
-- Adding Boost dependency assert
-- Adding Boost dependency config
-- Adding Boost dependency container
...
-- Adding Boost dependency container_hash
-- Adding Boost dependency core
-- Adding Boost dependency describe
-- Adding Boost dependency endian
-- Adding Boost dependency headers
-- Adding Boost dependency intrusive
-- Adding Boost library json
-- Adding Boost dependency move
-- Adding Boost dependency mp11
-- Adding Boost dependency predef
-- Adding Boost dependency static_assert
-- Adding Boost dependency system
-- Adding Boost dependency throw_exception
-- Adding Boost dependency variant2
-- Adding Boost dependency winapi
-- Configuring done

No Parser. Your result could be a consequence of -DBUILD_TESTING=Y not being parsed correctly.

[Flamefire]

No Parser. Your result could be a consequence of -DBUILD_TESTING=Y not being parsed correctly.

Actually that is expected right now: The dependency scanner doesn't parse the test CML but just adds all other libraries with EXCLUDE_FROM_ALL and w/o installation set. But it still does add them.
See boostorg/cmake#86

[grisumbras]

https://drone.cpp.al/boostorg/json/1916/22/2 <- this passes, which means JSON should work with CMake 3.8. However, according to boostorg/boost#1083, the minimum should be 3.9. Can you change the PR to use that?

[nigels-com]

@grisumbras Yes, happy to make that change to cmake-3.9.

[grisumbras]

Scratch that, according to boostorg/boost#1083 3.8 should work. So, please keep 3.8.

[Flamefire]

However, according to boostorg/boost#1083, the minimum should be 3.9.

Turns out that was a documentation bug and 3.8.0 does work for JSON.

[nigels-com]

There was one more fixup needed for cmake-3.8.
The find_package(BoostPrettyPrinters) portion requires cmake-3.12, but it seems optional.

[nigels-com]

Tested in combination with boostorg/cmake#86

$ PATH=/opt/cmake-3.8.0-Linux-x86_64/bin:$PATH cmake .. -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_COMPILER_LAUNCHER=ccache -DBUILD_TESTING=N -DCMAKE_CXX_COMPILER=clang++-18 -DBUILD_TESTING=Y -DBOOST_INCLUDE_LIBRARIES=json && ninja check
-- The CXX compiler identification is Clang 18.1.3
-- Check for working CXX compiler: /usr/bin/clang++-18
-- Check for working CXX compiler: /usr/bin/clang++-18 -- works
...
-- Generating done
-- Build files have been written to: /home/nigels/dev/boost/build
[69/69] cd /home/nigels/dev/boost/build && /opt/cmake-3.8.0-Linux-x86_64/bin/ctest --output-on-failure --no-tests=error -C Release
Test project /home/nigels/dev/boost/build
    Start 1: boost_json-tests
1/4 Test #1: boost_json-tests ...................   Passed    0.87 sec
    Start 2: boost_json-limits
2/4 Test #2: boost_json-limits ..................   Passed    0.00 sec
    Start 3: boost_json-no_exceptions
3/4 Test #3: boost_json-no_exceptions ...........   Passed    0.00 sec
    Start 4: boost_json-intrusive-macro-tests
4/4 Test #4: boost_json-intrusive-macro-tests ...   Passed    0.00 sec

100% tests passed, 0 tests failed out of 4

[cppalliance-bot]

An automated preview of the documentation is available at https://1106.json.prtest2.cppalliance.org/libs/json/doc/html/index.html

[grisumbras]

Thank you for your contribution.