split mesonlib into a package

Currently mesonlib does some import tricks to figure out whether it
needs to use windows or posix specific functions. This is a little
hacky, but works fine. However, the way the typing stubs are implemented
for the msvcrt and fnctl modules will cause mypy to fail on the other
platform, since the functions are not implemented.

To aleviate this (and for slightly cleaner design), I've split mesonlib
into a pacakge with three modules. A universal module contains all of
the platform agnositc code, a win32 module contains window specific
code, a posix module contains the posix specific code, and a platform
module contains no-op implementations. Then the package's __init__ file
imports all of the universal functions and all of the functions from the
approriate platform module, or the no-op versions as fallbacks. This
makes mypy happy, and avoids `if`ing all over the code to switch between
the platform specific code.

1 files changed, 39 insertions, 0 deletions

diff --git a/mesonbuild/mesonlib/win32.py b/mesonbuild/mesonlib/win32.py
new file mode 100644
index 0000000..0919ef7
--- /dev/null
+++ b/mesonbuild/mesonlib/win32.py
@@ -0,0 +1,39 @@
+# SPDX-license-identifier: Apache-2.0
+# Copyright 2012-2021 The Meson development team
+# Copyright © 2021 Intel Corporation
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Windows specific implementations of mesonlib functionality."""
+
+import msvcrt
+import typing as T
+
+from .universal import MesonException
+from .platform import BuildDirLock as BuildDirLockBase
+
+__all__ = ['BuildDirLock']
+
+class BuildDirLock(BuildDirLockBase):
+
+    def __enter__(self) -> None:
+        self.lockfile = open(self.lockfilename, 'w')
+        try:
+            msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_NBLCK, 1)
+        except (BlockingIOError, PermissionError):
+            self.lockfile.close()
+            raise MesonException('Some other Meson process is already using this build directory. Exiting.')
+
+    def __exit__(self, *args: T.Any) -> None:
+        msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_UNLCK, 1)
+        self.lockfile.close()