Enabling installation by default breaks projects using unity as meson subproject

[nirs]

Since #658, when a project is consuming unity via meson subproject, installing the project
also install unity headers, static library, and pkgconfig file. I think this is always
unwanted since unity is a testing tool and never a runtime requirement.

A minimal reproducer

$ tree
.
├── meson.build
└── subprojects
    └── unity.wrap

$ cat meson.build 
project('unity-repr', 'c')
dependency('unity', fallback: ['unity', 'unity_dep'])

$ cat subprojects/unity.wrap 
[wrap-git]
url = https://github.com/ThrowTheSwitch/Unity.git
revision = head

Example build and install:

$ meson setup build
The Meson build system
Version: 1.0.0
Source dir: /home/nsoffer/tmp/unity-repr
Build dir: /home/nsoffer/tmp/unity-repr/build
Build type: native build
Project name: unity-repr
Project version: undefined
C compiler for the host machine: ccache cc (gcc 12.2.1 "cc (GCC) 12.2.1 20221121 (Red Hat 12.2.1-4)")
C linker for the host machine: cc ld.bfd 2.38-25
Host machine cpu family: x86_64
Host machine cpu: x86_64
Found pkg-config: /usr/bin/pkg-config (1.8.0)
Found CMake: /usr/bin/cmake (3.25.2)
Run-time dependency unity found: NO (tried pkgconfig and cmake)
Looking for a fallback subproject for the dependency unity
Cloning into 'unity'...
remote: Enumerating objects: 6463, done.
remote: Counting objects: 100% (686/686), done.
remote: Compressing objects: 100% (340/340), done.
remote: Total 6463 (delta 421), reused 553 (delta 342), pack-reused 5777
Receiving objects: 100% (6463/6463), 6.79 MiB | 4.98 MiB/s, done.
Resolving deltas: 100% (4005/4005), done.

Executing subproject unity 

unity| Project name: unity
unity| Project version: 2.5.4
unity| C compiler for the host machine: ccache cc (gcc 12.2.1 "cc (GCC) 12.2.1 20221121 (Red Hat 12.2.1-4)")
unity| C linker for the host machine: cc ld.bfd 2.38-25
unity| Program auto/generate_test_runner.rb found: YES (/home/nsoffer/tmp/unity-repr/subprojects/unity/auto/generate_test_runner.rb)
unity| Build targets in project: 1
unity| Subproject unity finished.

Dependency unity from subproject subprojects/unity found: YES 2.5.4
Build targets in project: 1

unity-repr undefined

  Subprojects
    unity: YES

Found ninja-1.10.2 at /usr/bin/ninja

$ meson compile -C build
INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /usr/bin/ninja -C /home/nsoffer/tmp/unity-repr/build
ninja: Entering directory `/home/nsoffer/tmp/unity-repr/build'
[2/2] Linking static target subprojects/unity/libunity.a

$ meson install --dry-run -C build
ninja: Entering directory `/home/nsoffer/tmp/unity-repr/build'
ninja: no work to do.
Installing subprojects/unity/libunity.a to /usr/local/lib64
Installing /home/nsoffer/tmp/unity-repr/subprojects/unity/src/unity.h to /usr/local/include/unity/
Installing /home/nsoffer/tmp/unity-repr/subprojects/unity/src/unity_internals.h to /usr/local/include/unity/
Installing /home/nsoffer/tmp/unity-repr/build/meson-private/unity.pc to /usr/local/lib64/pkgconfig

Expected behavior

The expected behavior is not installing anything when unity is built as a subproject.

Workaround

There is a workaround, installing with:

meson install --skip-subprojects unity

But this workaround need to be repeated in every distro packaging your project.

See also

• subproject installs when project using it installs mesonbuild/meson#2550
• minstall: Add --skip-subprojects option mesonbuild/meson#8356