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, 10 insertions, 1 deletions

diff --git a/src/test/cpp/util/file_test.cc b/src/test/cpp/util/file_test.cc
index ab943a7bf9..21b0afca51 100644
--- a/src/test/cpp/util/file_test.cc
+++ b/src/test/cpp/util/file_test.cc
@@ -206,7 +206,7 @@ class CollectingDirectoryEntryConsumer : public DirectoryEntryConsumer {
   void Consume(const string& name, bool is_directory) override {
     // Strip the path prefix up to the `rootname` to ease testing on all
     // platforms.
-    int index = name.rfind(rootname);
+    size_t index = name.rfind(rootname);
     string key = (index == string::npos) ? name : name.substr(index);
     // Replace backslashes with forward slashes (necessary on Windows only).
     std::replace(key.begin(), key.end(), '\\', '/');
@@ -248,4 +248,13 @@ TEST(FileTest, ForEachDirectoryEntryTest) {
   ASSERT_EQ(consumer.entries, expected);
 }
 
+TEST(FileTest, IsDevNullTest) {
+  ASSERT_TRUE(IsDevNull("/dev/null"));
+  ASSERT_FALSE(IsDevNull("dev/null"));
+  ASSERT_FALSE(IsDevNull("/dev/nul"));
+  ASSERT_FALSE(IsDevNull("/dev/nulll"));
+  ASSERT_FALSE(IsDevNull(NULL));
+  ASSERT_FALSE(IsDevNull(""));
+}
+
 }  // namespace blaze_util