mesonlib: handle meson exe wrappers

There are cases when it is useful to wrap the main meson executable with
a script that sets up environment variables, passes --cross-file, etc.
For example, in a Yocto SDK, we need to point to the right meson.cross
so that everything "just works", and we need to alter CC, CXX, etc. In
such cases, it can happen that the "meson" found in the path is actually
a wrapper script that invokes the real meson, which may be in another
location (e.g. "meson.real" or similar).

Currently, in such a situation, meson gets confused because it tries to
invoke itself using the "meson" executable (which points to the wrapper
script) instead of the actual meson (which may be called "meson.real" or
similar). In fact, the wrapper script is not necessarily even Python, so
the whole thing fails.

Fix this by using Python imports to directly find mesonmain.py instead
of trying to detect it heuristically. In addition to fixing the wrapper
issue, this should make the detection logic much more robust.

1 files changed, 22 insertions, 0 deletions

diff --git a/run_tests.py b/run_tests.py
index 648e6ce..731d864 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -42,6 +42,28 @@ if mesonlib.is_windows() or mesonlib.is_cygwin():
 else:
     exe_suffix = ''
 
+def setup_pythonpath():
+    # Make sure python can import mesonbuild, even if we change directories as
+    # some tests do. Since sys.path is the final product of fairly complex code
+    # in site.py, it's hard to tell where each entry came from just by looking
+    # at sys.path, so we don't know if a given entry was set from a relative or
+    # absolute path. If an entry was set from a relative path, it won't
+    # continue to work if we change directories.  Instead of trying to guess
+    # where a given entry came from, just add the known-good mesonbuild to
+    # PYTHONPATH so that it will continue to be importable from other
+    # directories.
+    import mesonbuild
+    meson_dir = os.path.dirname(os.path.abspath(mesonbuild.__file__))
+    meson_root = os.path.realpath(os.path.join(meson_dir, os.pardir))
+    try:
+        python_path = os.environ['PYTHONPATH']
+    except KeyError:
+        python_path = meson_root
+    else:
+        paths = python_path.split(os.pathsep) + [meson_root]
+        python_path = os.pathsep.join(paths)
+    os.environ['PYTHONPATH'] = python_path
+
 def get_backend_args_for_dir(backend, builddir):
     '''
     Visual Studio backend needs to be given the solution to build