python dependency: fix embed handling for system dependency

Only search for and provide linkage to libpython, if the dependency
expects to be linked to it. Fixes overlinking on Linux / macOS when
pkg-config isn't installed and the sysconfig lookup is used instead.

This was correctly handled for pkg-config rather than deferring it until
use, since commit bf832743441a1171518d7a436164c989be679410 -- but that
handling neglected to cover sysconfig dependencies. And sysconfig would
always try to link to libpython, it just respected the dependency
configuration barely enough to allow falling back to "don't link" if
both link_libpython=False and the library wasn't found.

(cherry picked from commit d3148efe4f469412fbd1d7771b36e3082467979d)
[backported to apply pre-code move]

# Conflicts:
#	mesonbuild/dependencies/python.py

1 files changed, 15 insertions, 10 deletions

diff --git a/mesonbuild/modules/python.py b/mesonbuild/modules/python.py
index 7e4469e..9aa7705 100644
--- a/mesonbuild/modules/python.py
+++ b/mesonbuild/modules/python.py
@@ -96,7 +96,15 @@ class _PythonDependencyBase(_Base):
         self.platform = python_holder.platform
         self.variables = python_holder.variables
         self.paths = python_holder.paths
-        self.link_libpython = python_holder.link_libpython
+        # The "-embed" version of python.pc / python-config was introduced in 3.8,
+        # and distutils extension linking was changed to be considered a non embed
+        # usage. Before then, this dependency always uses the embed=True handling
+        # because that is the only one that exists.
+        #
+        # On macOS and some Linux distros (Debian) distutils doesn't link extensions
+        # against libpython, even on 3.7 and below. We call into distutils and
+        # mirror its behavior. See https://github.com/mesonbuild/meson/issues/4117
+        self.link_libpython = python_holder.link_libpython or embed
         self.info: T.Optional[T.Dict[str, str]] = None
         if mesonlib.version_compare(self.version, '>= 3.0'):
             self.major_version = 3
@@ -120,15 +128,8 @@ class PythonPkgConfigDependency(PkgConfigDependency, _PythonDependencyBase):
         if libpc and not self.is_found:
             mlog.debug(f'"python-{self.version}" could not be found in LIBPC, this is likely due to a relocated python installation')
 
-        # The "-embed" version of python.pc was introduced in 3.8, and distutils
-        # extension linking was changed to be considered a non embed usage. Before
-        # then, this dependency always uses the embed=True file because that is the
-        # only one that exists,
-        #
-        # On macOS and some Linux distros (Debian) distutils doesn't link extensions
-        # against libpython, even on 3.7 and below. We call into distutils and
-        # mirror its behavior. See https://github.com/mesonbuild/meson/issues/4117
-        if not self.embed and not self.link_libpython and mesonlib.version_compare(self.version, '< 3.8'):
+        # pkg-config files are usually accurate starting with python 3.8
+        if not self.link_libpython and mesonlib.version_compare(self.version, '< 3.8'):
             self.link_args = []
 
 
@@ -152,6 +153,10 @@ class PythonSystemDependency(SystemDependency, _PythonDependencyBase):
         else:
             self._find_libpy(installation, environment)
 
+        if not self.link_libpython:
+            # match pkg-config behavior
+            self.link_args = []
+
         if not self.clib_compiler.has_header('Python.h', '', environment, extra_args=self.compile_args):
             self.is_found = False