Bring Meson build definition more in line with CMake by dcbaker · Pull Request #4452 · nlohmann/json

dcbaker · 2024-09-09T17:53:40Z

Update the Meson build definition to use Meson best practices, and bring into alignment with the CMake build files.

Particularly, This changes the meson build to only expose a single target, like the CMake does, controlled by an option with the same name. It additionally exposes the GlobalUDLs and ImplicitConversions options, which have behavioral implementations a consumer may wish to control. I have not exposed other options as they don't seem to be important for behavior.

The options names do not have the JSON_ prefix, and Meson already has (sub)project option namespaces, so adding JSON_ would worse (-Dnlohmann_json:ImplicitConversions vs -Dnlohmann_json:JSON_ImplicitConversions).

Pull request checklist

Read the Contribution Guidelines for detailed information.

Changes are described in the pull request, or an existing issue is referenced.
The test suite compiles and runs without error.
Code coverage is 100%. Test cases can be added by editing the test suite.
The source code is amalgamated; that is, after making changes to the sources in the include/nlohmann directory, run make amalgamate to create the single-header files single_include/nlohmann/json.hpp and single_include/nlohmann/json_fwd.hpp. The whole process is described here.

nlohmann · 2024-09-13T12:23:12Z

Is meson_options.txt really needed? If so, can it be moved into a subdirectory?

dcbaker · 2024-09-13T16:24:39Z

Meson options must be specified in a meson_options.txt (or for fairly new versions of Meson in a meson.options file), and that file has to be in the same directory as the root meson.build file. Meson options are read-only from the meson.build files, and are read in before the parsing of the meson.build file starts.

github-actions · 2025-01-19T00:12:01Z

This pull request has been marked as stale because it has had no activity for 30 days. While we won’t close it automatically, we encourage you to update or comment if it is still relevant. Keeping pull requests active and up-to-date helps us review and merge changes more efficiently. Thank you for your contributions!

dcbaker · 2025-01-19T01:27:02Z

I know that the meson_options.txt seems to be a blocker here, if I opened a new PR with the patches up until meson_options.txt is added, would that allow those changes to move faster?

nlohmann · 2025-01-19T15:31:06Z

How is this related to #3885?

dcbaker · 2025-01-19T18:24:59Z

It's not at all. I can comment there.

nlohmann · 2025-01-19T18:27:56Z

Please do - I don't know Meson and will not be able to solve any of these issues.

heitbaum · 2025-01-20T02:00:55Z

This PR improves the meson build significantly. All the headers are now being installed. It doesn’t address the .cmake files (but that is a seperate issue.)

it would be good to see this merged.

#3885 (comment)

./usr/lib/pkgconfig/nlohmann_json.pc
./usr/include/nlohmann/detail/string_concat.hpp
./usr/include/nlohmann/detail/string_escape.hpp
./usr/include/nlohmann/detail/value_t.hpp
./usr/include/nlohmann/detail/macro_scope.hpp
./usr/include/nlohmann/detail/abi_macros.hpp
./usr/include/nlohmann/detail/iterators/iter_impl.hpp
./usr/include/nlohmann/detail/iterators/primitive_iterator.hpp
./usr/include/nlohmann/detail/iterators/json_reverse_iterator.hpp
./usr/include/nlohmann/detail/iterators/iteration_proxy.hpp
./usr/include/nlohmann/detail/iterators/iterator_traits.hpp
./usr/include/nlohmann/detail/iterators/internal_iterator.hpp
./usr/include/nlohmann/detail/hash.hpp
./usr/include/nlohmann/detail/input/lexer.hpp
./usr/include/nlohmann/detail/input/json_sax.hpp
./usr/include/nlohmann/detail/input/input_adapters.hpp
./usr/include/nlohmann/detail/input/position_t.hpp
./usr/include/nlohmann/detail/input/binary_reader.hpp
./usr/include/nlohmann/detail/input/parser.hpp
./usr/include/nlohmann/detail/exceptions.hpp
./usr/include/nlohmann/detail/json_custom_base_class.hpp
./usr/include/nlohmann/detail/conversions/to_json.hpp
./usr/include/nlohmann/detail/conversions/from_json.hpp
./usr/include/nlohmann/detail/conversions/to_chars.hpp
./usr/include/nlohmann/detail/json_ref.hpp
./usr/include/nlohmann/detail/output/serializer.hpp
./usr/include/nlohmann/detail/output/binary_writer.hpp
./usr/include/nlohmann/detail/output/output_adapters.hpp
./usr/include/nlohmann/detail/json_pointer.hpp
./usr/include/nlohmann/detail/meta/is_sax.hpp
./usr/include/nlohmann/detail/meta/type_traits.hpp
./usr/include/nlohmann/detail/meta/identity_tag.hpp
./usr/include/nlohmann/detail/meta/detected.hpp
./usr/include/nlohmann/detail/meta/cpp_future.hpp
./usr/include/nlohmann/detail/meta/void_t.hpp
./usr/include/nlohmann/detail/meta/call_std/end.hpp
./usr/include/nlohmann/detail/meta/call_std/begin.hpp
./usr/include/nlohmann/detail/meta/std_fs.hpp
./usr/include/nlohmann/detail/macro_unscope.hpp
./usr/include/nlohmann/adl_serializer.hpp
./usr/include/nlohmann/json_fwd.hpp
./usr/include/nlohmann/thirdparty/hedley/hedley_undef.hpp
./usr/include/nlohmann/thirdparty/hedley/hedley.hpp
./usr/include/nlohmann/ordered_map.hpp
./usr/include/nlohmann/json.hpp
./usr/include/nlohmann/byte_container_with_subtype.hpp

dcbaker · 2025-01-20T19:53:18Z

I've rebased on the current develop branch to fix conflicts and added my signed-off-by

coveralls · 2025-01-20T20:21:32Z

coverage: 99.191%. remained the same
when pulling 30c24bf on dcbaker:submit/meson-updates
into 034f3ec on nlohmann:develop.

nlohmann

Please also document meson.build and meson_options.txt in FILES.md.

nlohmann · 2025-01-22T20:58:19Z

+    'MultipleHeaders',
+    type: 'boolean',
+    value: true,
+    description: 'Use non-amalgomated version of the library',


Suggested change

description: 'Use non-amalgomated version of the library',

description: 'Use non-amalgamated version of the library',

nlohmann · 2025-01-22T20:59:29Z

+    type: 'boolean',
+    value: true,
+    description: 'Enable implicit conversions',
+)


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.

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.

@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?

Sounds plausible, but I would not know how :)

github-actions · 2025-02-28T00:11:14Z

This pull request has been marked as stale because it has had no activity for 30 days. While we won’t close it automatically, we encourage you to update or comment if it is still relevant. Keeping pull requests active and up-to-date helps us review and merge changes more efficiently. Thank you for your contributions!

for better readability Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

Without a version set meson will give no developer warnings, including deprecations. 0.64 was selected as it's quite old, it's the newest version supported by muon (a pure C Meson implementation), and there's nothing complicated going on here. Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

This simplifies the use of json as a subproject. Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

This makes a single call to install the entire directory, and doesn't need an update if any new headers are added. It also will simplify bringing the Meson and CMake builds into allignment on how they handle the multi-header vs single-header setups. Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

Matching the CMake as closely as possible, as Meson doesn't have C++11 feature checks like CMAke does. Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

This uses a meson option (set in `meson_options.txt`) to control whether multi-header or single-header setup is wanted. Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

dcbaker · 2025-10-31T19:27:17Z

I had forgotten about this, oops.

This still needs more work, but I've rebased on the devel branch and added some Meson information to the FILES.md file.

I want to look at the pkg config file thing some more as there is some discrepency between the .pc file and the cmake export files.

Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

github-actions · 2025-12-01T00:16:22Z

This pull request has been marked as stale because it has had no activity for 30 days. While we won’t close it automatically, we encourage you to update or comment if it is still relevant. Keeping pull requests active and up-to-date helps us review and merge changes more efficiently. Thank you for your contributions!

dcbaker requested a review from nlohmann as a code owner September 9, 2024 17:53

github-actions Bot added M CMake labels Sep 9, 2024

dcbaker mentioned this pull request Sep 9, 2024

Provide nlohmann/json dependency with multiple headers mesonbuild/wrapdb#1678

Closed

dcbaker force-pushed the submit/meson-updates branch from 138d391 to 641e353 Compare September 9, 2024 18:39

gregmarr reviewed Sep 9, 2024

View reviewed changes

Comment thread meson.build Outdated

dcbaker force-pushed the submit/meson-updates branch 2 times, most recently from 5b5adfe to b65e362 Compare September 9, 2024 20:20

github-actions Bot added the state: stale the issue has not been updated in a while and will be closed automatically soon unless it is updated label Jan 19, 2025

github-actions Bot removed the state: stale the issue has not been updated in a while and will be closed automatically soon unless it is updated label Jan 20, 2025

nlohmann added the please rebase Please rebase your branch to origin/develop label Jan 20, 2025

heitbaum mentioned this pull request Jan 20, 2025

meson build does not install nlohmann_json*.cmake files #3885

Open

2 tasks

dcbaker force-pushed the submit/meson-updates branch from b65e362 to 7f44940 Compare January 20, 2025 19:50

github-actions Bot removed the CMake label Jan 20, 2025

dcbaker force-pushed the submit/meson-updates branch from 7f44940 to e40b32d Compare January 20, 2025 19:52

nlohmann removed the please rebase Please rebase your branch to origin/develop label Jan 20, 2025

nlohmann requested changes Jan 22, 2025

View reviewed changes

github-actions Bot added the state: stale the issue has not been updated in a while and will be closed automatically soon unless it is updated label Feb 28, 2025

meson: Indent code inside an if block

7188a4a

for better readability Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

dcbaker added 7 commits October 31, 2025 12:23

meson: use override_dependency() to set dependencies

42f30ff

This simplifies the use of json as a subproject. Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

meson: set the C++ standard to C++11

76d91cd

Matching the CMake as closely as possible, as Meson doesn't have C++11 feature checks like CMAke does. Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

meson: handle single header and multiheader the same way CMake does

da826f1

This uses a meson option (set in `meson_options.txt`) to control whether multi-header or single-header setup is wanted. Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

meson: add support for the GlobalUDLs option

6664d32

Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

meson: add support for the ImplictConversions option

1836685

Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

dcbaker force-pushed the submit/meson-updates branch from e40b32d to 56d1f64 Compare October 31, 2025 19:25

Add meson information to FILES.md

30c24bf

Signed-off-by: Dylan Baker <dylan@pnwbakers.com>

dcbaker force-pushed the submit/meson-updates branch from 56d1f64 to 30c24bf Compare October 31, 2025 19:27

nlohmann removed the state: stale the issue has not been updated in a while and will be closed automatically soon unless it is updated label Oct 31, 2025

github-actions Bot added the state: stale the issue has not been updated in a while and will be closed automatically soon unless it is updated label Dec 1, 2025

	description: 'Use non-amalgomated version of the library',
	description: 'Use non-amalgamated version of the library',

Uh oh!

Conversation

dcbaker commented Sep 9, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Pull request checklist

Uh oh!

Uh oh!

nlohmann commented Sep 13, 2024

Uh oh!

dcbaker commented Sep 13, 2024

Uh oh!

github-actions Bot commented Jan 19, 2025

Uh oh!

dcbaker commented Jan 19, 2025

Uh oh!

nlohmann commented Jan 19, 2025

Uh oh!

dcbaker commented Jan 19, 2025

Uh oh!

nlohmann commented Jan 19, 2025

Uh oh!

heitbaum commented Jan 20, 2025

Uh oh!

dcbaker commented Jan 20, 2025

Uh oh!

coveralls commented Jan 20, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

nlohmann left a comment

Choose a reason for hiding this comment

Uh oh!

nlohmann Jan 22, 2025

Choose a reason for hiding this comment

Uh oh!

nlohmann Jan 22, 2025

Choose a reason for hiding this comment

Uh oh!

dcbaker Jan 23, 2025

Choose a reason for hiding this comment

Uh oh!

dcbaker Jan 27, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

nlohmann Jan 28, 2025

Choose a reason for hiding this comment

Uh oh!

github-actions Bot commented Feb 28, 2025

Uh oh!

dcbaker commented Oct 31, 2025

Uh oh!

github-actions Bot commented Dec 1, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

dcbaker commented Sep 9, 2024 •

edited

Loading

coveralls commented Jan 20, 2025 •

edited

Loading

dcbaker Jan 27, 2025 •

edited

Loading