From 696bbb8ed07706fef46e826c3a90eaffddf4589a Mon Sep 17 00:00:00 2001
From: Dylan Baker <dylan@pnwbakers.com>
Date: Thu, 7 Dec 2023 11:51:40 -0800
Subject: [PATCH] python: attempt to make dependency work correctly when cross
 compiling

TODO: write helpful message
---
 mesonbuild/dependencies/python.py | 41 ++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/mesonbuild/dependencies/python.py b/mesonbuild/dependencies/python.py
index 9aea6bda83fb..300abc939b21 100644
--- a/mesonbuild/dependencies/python.py
+++ b/mesonbuild/dependencies/python.py
@@ -25,7 +25,7 @@
 from .framework import ExtraFrameworkDependency
 from .pkgconfig import PkgConfigDependency
 from ..environment import detect_cpu_family
-from ..programs import ExternalProgram
+from ..programs import ExternalProgram, find_external_program
 
 if T.TYPE_CHECKING:
     from typing_extensions import TypedDict
@@ -193,8 +193,11 @@ def __init__(self, name: str, environment: 'Environment',
 class PythonSystemDependency(SystemDependency, _PythonDependencyBase):
 
     def __init__(self, name: str, environment: 'Environment',
-                 kwargs: T.Dict[str, T.Any], installation: 'BasicPythonExternalProgram'):
+                 kwargs: T.Dict[str, T.Any], installation: T.Optional[BasicPythonExternalProgram]):
         SystemDependency.__init__(self, name, environment, kwargs)
+        if installation is None:
+            self.is_found = False
+            return
         _PythonDependencyBase.__init__(self, installation, kwargs.get('embed', False))
 
         # match pkg-config behavior
@@ -358,15 +361,27 @@ def python_factory(env: 'Environment', for_machine: 'MachineChoice',
     methods = process_method_kw({DependencyMethods.PKGCONFIG, DependencyMethods.SYSTEM}, kwargs)
     embed = kwargs.get('embed', False)
     candidates: T.List['DependencyGenerator'] = []
-    from_installation = installation is not None
-    # When not invoked through the python module, default installation.
+
+    # when we're not running from a provided installation, create one using the
+    # appropriate python from the cross file or native file, or fall back to the
+    # running python for the host machine.
     if installation is None:
-        installation = BasicPythonExternalProgram('python3', mesonlib.python_command)
-        installation.sanity()
-    pkg_version = installation.info['variables'].get('LDVERSION') or installation.info['version']
+        if not (env.is_cross_build() and env.need_exe_wrapper() and env.exe_wrapper is None):
+            cmd: T.List[str] = []
+            for prog in find_external_program(env, for_machine, 'python3', 'python3', ['python3', 'python'], allow_default_for_cross=False):
+                if prog.found():
+                    cmd = T.cast('T.List[str]', prog.command)
+                    break
+            else:
+                if not (env.is_cross_build() and for_machine is mesonlib.MachineChoice.HOST):
+                    cmd = mesonlib.python_command
+            if cmd:
+                installation = BasicPythonExternalProgram('python3', cmd)
+                installation.sanity()
 
     if DependencyMethods.PKGCONFIG in methods:
-        if from_installation:
+        if installation is not None:
+            pkg_version = installation.info['variables'].get('LDVERSION') or installation.info['version']
             pkg_libdir = installation.info['variables'].get('LIBPC')
             pkg_embed = '-embed' if embed and mesonlib.version_compare(installation.info['version'], '>=3.8') else ''
             pkg_name = f'python-{pkg_version}{pkg_embed}'
@@ -407,10 +422,12 @@ def set_env(name: str, value: str) -> None:
 
     if DependencyMethods.EXTRAFRAMEWORK in methods:
         nkwargs = kwargs.copy()
-        if mesonlib.version_compare(pkg_version, '>= 3'):
-            # There is a python in /System/Library/Frameworks, but that's python 2.x,
-            # Python 3 will always be in /Library
-            nkwargs['paths'] = ['/Library/Frameworks']
+        if installation is not None:
+            pkg_version = installation.info['variables'].get('LDVERSION') or installation.info['version']
+            if mesonlib.version_compare(pkg_version, '>= 3'):
+                # There is a python in /System/Library/Frameworks, but that's python 2.x,
+                # Python 3 will always be in /Library
+                nkwargs['paths'] = ['/Library/Frameworks']
         candidates.append(functools.partial(PythonFrameworkDependency, 'Python', env, nkwargs, installation))
 
     return candidates