Reuse old build dir on Windows

Summary:
getdeps.py's find_existing_win32_subst_for_path function tries to reuse an existing build directory alias. (On Windows, the build directory is aliased to a drive letter to shorten paths.) If this function does not find and existing build directory alias, getdeps.py invalidates many of its caches.

On my Windows machine, find_existing_win32_subst_for_path always fails, so all of my builds are super slow. This happens because find_existing_win32_subst_for_path is given a path with a lower-case drive letter ("c:\users\..."), but the subst command returns paths with an upper-case drive letter ("C:\users\...").

When comparing paths, use ntpath.normpath. This makes the comparison case-insensitive for drive letters. (It also makes the comparison case-insensitive for other path components.)

On Linux and macOS, this diff should not change behavior.

Reviewed By: wez

Differential Revision: D15466096

fbshipit-source-id: 1669aa0a6eaeb6012154f3a9e24eba3f835262c6

build/fbcode_builder/getdeps/test/scratch_test.py

@@ -0,0 +1,83 @@
+#!/usr/bin/env python
+# Copyright (c) 2019-present, Facebook, Inc.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree. An additional grant
+# of patent rights can be found in the PATENTS file in the same directory.
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import unittest
+
+from ..buildopts import find_existing_win32_subst_for_path
+
+
+class Win32SubstTest(unittest.TestCase):
+    def test_no_existing_subst(self):
+        self.assertIsNone(
+            find_existing_win32_subst_for_path(
+                r"C:\users\alice\appdata\local\temp\fbcode_builder_getdeps",
+                subst_mapping={},
+            )
+        )
+        self.assertIsNone(
+            find_existing_win32_subst_for_path(
+                r"C:\users\alice\appdata\local\temp\fbcode_builder_getdeps",
+                subst_mapping={"X:\\": r"C:\users\alice\appdata\local\temp\other"},
+            )
+        )
+
+    def test_exact_match_returns_drive_path(self):
+        self.assertEqual(
+            find_existing_win32_subst_for_path(
+                r"C:\temp\fbcode_builder_getdeps",
+                subst_mapping={"X:\\": r"C:\temp\fbcode_builder_getdeps"},
+            ),
+            "X:\\",
+        )
+        self.assertEqual(
+            find_existing_win32_subst_for_path(
+                r"C:/temp/fbcode_builder_getdeps",
+                subst_mapping={"X:\\": r"C:/temp/fbcode_builder_getdeps"},
+            ),
+            "X:\\",
+        )
+
+    def test_multiple_exact_matches_returns_arbitrary_drive_path(self):
+        self.assertIn(
+            find_existing_win32_subst_for_path(
+                r"C:\temp\fbcode_builder_getdeps",
+                subst_mapping={
+                    "X:\\": r"C:\temp\fbcode_builder_getdeps",
+                    "Y:\\": r"C:\temp\fbcode_builder_getdeps",
+                    "Z:\\": r"C:\temp\fbcode_builder_getdeps",
+                },
+            ),
+            ("X:\\", "Y:\\", "Z:\\"),
+        )
+
+    def test_drive_letter_is_case_insensitive(self):
+        self.assertEqual(
+            find_existing_win32_subst_for_path(
+                r"C:\temp\fbcode_builder_getdeps",
+                subst_mapping={"X:\\": r"c:\temp\fbcode_builder_getdeps"},
+            ),
+            "X:\\",
+        )
+
+    def test_path_components_are_case_insensitive(self):
+        self.assertEqual(
+            find_existing_win32_subst_for_path(
+                r"C:\TEMP\FBCODE_builder_getdeps",
+                subst_mapping={"X:\\": r"C:\temp\fbcode_builder_getdeps"},
+            ),
+            "X:\\",
+        )
+        self.assertEqual(
+            find_existing_win32_subst_for_path(
+                r"C:\temp\fbcode_builder_getdeps",
+                subst_mapping={"X:\\": r"C:\TEMP\FBCODE_builder_getdeps"},
+            ),
+            "X:\\",
+        )