dependencies: add pybind11 custom factory

This works with pkg-config and cmake without any special support. The
custom factory adds further support for config-tool, via
`pybind11-config`. This is useful because the config-tool will work out
of the box when pybind11 is installed, but the pkg-config and cmake
files are shoved into python's site-packages, which is an unfortunate
distribution model and makes it impossible to use in an out of the box
manner.

It's possible to manually set up the PKG_CONFIG_PATH to detect it
anyway, but in case that does not happen, having the config-tool
fallback is extremely useful.

docs/markdown/Dependencies.md

@@ -659,6 +659,12 @@ The `language` keyword may used.
 
 `method` may be `auto`, `config-tool` or `pkg-config`.
 
+## Pybind11
+
+*(added 1.1.0)*
+
+`method` may be `auto`, `pkg-config`, `config-tool`, or `cmake`.
+
 ## Python3
 
 Python3 is handled specially by Meson:

docs/markdown/snippets/pybind11_dep.md

@@ -0,0 +1,9 @@
+## New pybind11 custom dependency
+
+`dependency('pybind11')` works with pkg-config and cmake without any special
+support, but did not handle the `pybind11-config` script.
+
+This is useful because the config-tool will work out of the box when pybind11
+is installed, but the pkg-config and cmake files are shoved into python's
+site-packages, which makes it impossible to use in an out of the box manner.
+

mesonbuild/dependencies/__init__.py

@@ -39,7 +39,7 @@
     dl_factory, openssl_factory, libcrypto_factory, libssl_factory,
 )
 from .platform import AppleFrameworks
-from .python import python_factory as python3_factory
+from .python import python_factory as python3_factory, pybind11_factory
 from .qt import qt4_factory, qt5_factory, qt6_factory
 from .ui import GnuStepDependency, WxDependency, gl_factory, sdl2_factory, vulkan_factory
 
@@ -270,6 +270,7 @@ def __init__(self, name: str, environment: 'Environment', kwargs: T.Dict[str, T.
 
     # from python:
     'python3': python3_factory,
+    'pybind11': pybind11_factory,
 
     # From ui:
     'gl': gl_factory,

mesonbuild/dependencies/python.py

@@ -19,6 +19,8 @@
 
 from .. import mesonlib, mlog
 from .base import process_method_kw, DependencyMethods, DependencyTypeName, ExternalDependency, SystemDependency
+from .configtool import ConfigToolDependency
+from .factory import DependencyFactory
 from .framework import ExtraFrameworkDependency
 from .pkgconfig import PkgConfigDependency
 from ..environment import detect_cpu_family
@@ -49,6 +51,21 @@ class PythonIntrospectionDict(TypedDict):
     _Base = object
 
 
+class Pybind11ConfigToolDependency(ConfigToolDependency):
+
+    tools = ['pybind11-config']
+
+    # pybind11 in 2.10.4 added --version, sanity-check another flag unique to it
+    # in the meantime
+    skip_version = '--pkgconfigdir'
+
+    def __init__(self, name: str, environment: Environment, kwargs: T.Dict[str, T.Any]):
+        super().__init__(name, environment, kwargs)
+        if not self.is_found:
+            return
+        self.compile_args = self.get_config_value(['--includes'], 'compile_args')
+
+
 class BasicPythonExternalProgram(ExternalProgram):
     def __init__(self, name: str, command: T.Optional[T.List[str]] = None,
                  ext_prog: T.Optional[ExternalProgram] = None):
@@ -371,3 +388,9 @@ def set_env(name: str, value: str) -> None:
         candidates.append(functools.partial(PythonFrameworkDependency, 'Python', env, nkwargs, installation))
 
     return candidates
+
+pybind11_factory = DependencyFactory(
+    'pybind11',
+    [DependencyMethods.PKGCONFIG, DependencyMethods.CONFIG_TOOL, DependencyMethods.CMAKE],
+    configtool_class=Pybind11ConfigToolDependency,
+)