how does meson generate a build file when fetching a subproject with a .wrap file

[BruceLi686]

In a meson project, i found it seems to automatically generate a meson.build file for a downloaded subproject according to the subproject's .wrap file. Is it true? How does meson achieve that? I'm a newbie to meson, could anyone guide me?

[QuLogic]

There is no automatic generation; that project has a meson.build: https://github.com/nlohmann/json/blob/develop/meson.build

[BruceLi686]

I take a bad example. Below is a new example to illustrate my question.

In original socket.io-client-cpp.git, no meson.build file. But you can note there's a 'patch_directory' entry in .wrap file. Then meson will copy the meson.build file from sioclient in packagefiles. This is the overlay mechanism of meson, details see https://mesonbuild.com/Wrap-dependency-system-manual.html#accepted-configuration-properties-for-wraps .

Thanks @QuLogic for your reply.

[eli-schwartz]

it seems to automatically generate a meson.build file for a downloaded subproject according to the subproject's .wrap file. Is it true? How does meson achieve that?

No. A wrap file indicates that the entire source code for the subproject is downloaded from elsewhere. This includes both the .hpp / .cpp / '.h' / '.c' files (and others) as well as the meson.build itself. In cases where the upstream project doesn't have a meson.build file in their source code tarball, a .wrap file may specify two archives to download, one of which contains the upstream source code and the other containing the meson.build file(s).

[BruceLi686]

Yes. The .wrap file defines a patch_directory entry, then any files/archive placed in subprojects/packagefiles/%patch_directory% will be overlayed.

Thank you 😊 @eli-schwartz .