Bazel client: add blaze_util::IsDevNull

Add a method to test if a path is /dev/null (or
case-insensitive "NUL" on Windows), and use it in
blaze::MakeAbsolute.

In this commit:
- implement blaze_util::IsDevNull with POSIX and
  Windows semantics + add tests
- blaze::MakeAbsolute calls blaze::ConvertPath
  on its input to convert MSYS paths on Windows
- blaze_util::GetCwdW (thus GetCwd) always returns
  a lowercase path so that it is deterministic
- blaze_util::GetCurrentDrive returns lowercase
  letter to be consisent with blaze::ConvertPath,
  which also returns a lowercase path

Fixes https://github.com/bazelbuild/bazel/issues/3440

Change-Id: I3af5ba0a033d542fe64a676d67f27472298d1089
PiperOrigin-RevId: 163038503

1 files changed, 1 insertions, 0 deletions

diff --git a/src/test/cpp/blaze_util_test.cc b/src/test/cpp/blaze_util_test.cc
index a06e8e0a01..ac3165c642 100644
--- a/src/test/cpp/blaze_util_test.cc
+++ b/src/test/cpp/blaze_util_test.cc
@@ -264,6 +264,7 @@ TEST_F(BlazeUtilTest, MakeAbsolute) {
   EXPECT_EQ(MakeAbsolute("foo"), blaze_util::GetCwd() + "/foo");
 #endif
   EXPECT_EQ(MakeAbsolute(std::string()), blaze_util::GetCwd());
+  EXPECT_EQ(MakeAbsolute("/dev/null"), "/dev/null");
 }
 
 }  // namespace blaze