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Bring Meson build definition more in line with CMake #4452

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Bring Meson build definition more in line with CMake #4452

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e07b096
meson: Indent code inside an if block
dcbaker Sep 9, 2024
cf80e33
meson: set a minimum Meson version
dcbaker Sep 9, 2024
ea92dd8
meson: use `override_dependency()` to set dependencies
dcbaker Sep 9, 2024
6fede3b
meson: use `install_subdir` for headers
dcbaker Sep 9, 2024
df7ec72
meson: set the C++ standard to C++11
dcbaker Sep 9, 2024
af894c3
meson: handle single header and multiheader the same way CMake does
dcbaker Sep 9, 2024
a079ed8
meson: add support for the GlobalUDLs option
dcbaker Sep 9, 2024
e40b32d
meson: add support for the ImplictConversions option
dcbaker Sep 9, 2024
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40 changes: 28 additions & 12 deletions meson.build
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Original file line number Diff line number Diff line change
Expand Up @@ -2,23 +2,39 @@ project('nlohmann_json',
'cpp',
version : '3.11.3',
license : 'MIT',
meson_version : '>= 0.64',
default_options: ['cpp_std=c++11'],
)

nlohmann_json_dep = declare_dependency(
include_directories: include_directories('single_include')
)
if get_option('MultipleHeaders')
incdir = 'include'
else
incdir = 'single_include'
endif

nlohmann_json_multiple_headers = declare_dependency(
include_directories: include_directories('include')
cpp_args = [
'-DJSON_USE_GLOBAL_UDLS=@0@'.format(
(not get_option('GlobalUDLs')).to_int()),
'-DJSON_USE_IMPLICIT_CONVERSIONS=@0@'.format(
(not get_option('ImplicitConversions')).to_int()),
]

nlohmann_json_dep = declare_dependency(
compile_args: cpp_args,
include_directories: include_directories(incdir)
)
meson.override_dependency('nlohmann_json', nlohmann_json_dep)

if not meson.is_subproject()
install_headers('single_include/nlohmann/json.hpp', subdir: 'nlohmann')
install_headers('single_include/nlohmann/json_fwd.hpp', subdir: 'nlohmann')
install_subdir(
incdir / 'nlohmann',
install_dir: get_option('includedir'),
install_tag: 'devel',
)

pkgc = import('pkgconfig')
pkgc.generate(name: 'nlohmann_json',
version: meson.project_version(),
description: 'JSON for Modern C++'
)
pkgc = import('pkgconfig')
pkgc.generate(name: 'nlohmann_json',
version: meson.project_version(),
description: 'JSON for Modern C++'
)
endif
18 changes: 18 additions & 0 deletions meson_options.txt
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@@ -0,0 +1,18 @@
option(
'MultipleHeaders',
type: 'boolean',
value: true,
description: 'Use non-amalgomated version of the library',
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Suggested change
description: 'Use non-amalgomated version of the library',
description: 'Use non-amalgamated version of the library',

)
option(
'GlobalUDLs',
type: 'boolean',
value: true,
description: 'Place user-defined string literals in the global namespace',
)
option(
'ImplicitConversions',
type: 'boolean',
value: true,
description: 'Enable implicit conversions',
)
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There are more flags, see https://json.nlohmann.me/integration/cmake/#cmake-options for example. Though not are equally interesting, I wonder why here only theres three have been selected.

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It's been a while, I remember for sure that the MultipleHeaders option is essential to get the same behavior out of Meson and CMake, especially when using the Meson definitions in an embedded project. I don't remember why I added the other two.

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@dcbaker dcbaker Jan 27, 2025 •
edited
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@nlohmann: I looked more, and I'm pretty sure that the reason that I added those two options in particular is that the related defines are exposed publicly in the pkg-config file. So for Meson and CMake to generate equivalent .pc files we'd need that.

Now that I'm looking at the generated CMake Target, it looks like JSON_DISABLE_ENUM_SERIALIZATION, JSON_DIAGNOSTICS, JSON_DIAGNOSTIC_POSITIONS, and JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON are exposed in CMake, so maybe we should update the pkg-config CMake generates to expose those as well?

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Sounds plausible, but I would not know how :)

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