new custom dependency lookup for libdl

docs/markdown/Dependencies.md

@@ -393,6 +393,17 @@ foreach h : check_headers
 endforeach
 ```
 
+## dl (libdl)
+
+*(added 0.62.0)*
+
+Provides access to the dynamic link interface (functions: dlopen,
+dlclose, dlsym and others). On systems where this is not built
+into libc (mostly glibc < 2.34), tries to find an external library
+providing them instead.
+
+`method` may be `auto`, `builtin` or `system`.
+
 ## Fortran Coarrays
 
 *(added 0.50.0)*

docs/markdown/snippets/libdl-dependency.md

@@ -0,0 +1,8 @@
+## New custom dependency for libdl
+
+```
+dependency('dl')
+```
+
+will now check for the functionality of libdl.so, but first check if it is
+provided in the libc (for example in libc on OpenBSD or in musl libc on linux).

mesonbuild/dependencies/__init__.py

@@ -36,6 +36,7 @@ from .misc import (
     BlocksDependency, OpenMPDependency, cups_factory, curses_factory, gpgme_factory,
     libgcrypt_factory, libwmf_factory, netcdf_factory, pcap_factory, python3_factory,
     shaderc_factory, threads_factory, ThreadDependency, iconv_factory, intl_factory,
+    dl_factory
 )
 from .platform import AppleFrameworks
 from .qt import qt4_factory, qt5_factory, qt6_factory
@@ -254,6 +255,7 @@ packages.update({
     'shaderc': shaderc_factory,
     'iconv': iconv_factory,
     'intl': intl_factory,
+    'dl': dl_factory,
 
     # From platform:
     'appleframeworks': AppleFrameworks,

mesonbuild/dependencies/misc.py

@@ -60,6 +60,25 @@ def netcdf_factory(env: 'Environment',
     return candidates
 
 
+class DlBuiltinDependency(BuiltinDependency):
+    def __init__(self, name: str, env: 'Environment', kwargs: T.Dict[str, T.Any]):
+        super().__init__(name, env, kwargs)
+
+        if self.clib_compiler.has_function('dlopen', '#include <dlfcn.h>', env)[0]:
+            self.is_found = True
+
+
+class DlSystemDependency(SystemDependency):
+    def __init__(self, name: str, env: 'Environment', kwargs: T.Dict[str, T.Any]):
+        super().__init__(name, env, kwargs)
+
+        h = self.clib_compiler.has_header('dlfcn.h', '', env)
+        self.link_args = self.clib_compiler.find_library('dl', env, [], self.libtype)
+
+        if h[0] and self.link_args:
+            self.is_found = True
+
+
 class OpenMPDependency(SystemDependency):
     # Map date of specification release (which is the macro value) to a version.
     VERSIONS = {
@@ -559,6 +578,13 @@ cups_factory = DependencyFactory(
     cmake_name='Cups',
 )
 
+dl_factory = DependencyFactory(
+    'dl',
+    [DependencyMethods.BUILTIN, DependencyMethods.SYSTEM],
+    builtin_class=DlBuiltinDependency,
+    system_class=DlSystemDependency,
+)
+
 gpgme_factory = DependencyFactory(
     'gpgme',
     [DependencyMethods.PKGCONFIG, DependencyMethods.CONFIG_TOOL],