3 files changed, 57 insertions, 7 deletions
diff --git a/src/main/cpp/util/file_posix.cc b/src/main/cpp/util/file_posix.cc
index f4890a0294..466bae499d 100644
--- a/src/main/cpp/util/file_posix.cc
+++ b/src/main/cpp/util/file_posix.cc
@@ -248,12 +248,12 @@ bool CanAccess(const string& path, bool read, bool write, bool exec) {
   return access(path.c_str(), mode) == 0;
 }
 
+#ifndef __CYGWIN__
 bool IsDirectory(const string& path) {
   struct stat buf;
   return stat(path.c_str(), &buf) == 0 && S_ISDIR(buf.st_mode);
 }
 
-#ifndef __CYGWIN__
 bool IsRootDirectory(const string &path) {
   return path.size() == 1 && path[0] == '/';
 }
diff --git a/src/main/cpp/util/file_windows.cc b/src/main/cpp/util/file_windows.cc
index 2b4a105f05..3a5b5ac8e4 100644
--- a/src/main/cpp/util/file_windows.cc
+++ b/src/main/cpp/util/file_windows.cc
@@ -38,6 +38,11 @@ using std::wstring;
 // The result may have a UNC prefix.
 static unique_ptr<WCHAR[]> GetCwdW();
 
+// Returns true if `path` refers to a directory or (non-dangling) junction.
+// `path` must be a normalized Windows path, with UNC prefix (and absolute) if
+// necessary.
+static bool IsDirectoryW(const wstring& path);
+
 // Like `AsWindowsPath` but the result is absolute and has UNC prefix if needed.
 static bool AsWindowsPathWithUncPrefix(const string& path, wstring* wpath);
 
@@ -551,14 +556,23 @@ bool CanAccess(const string& path, bool read, bool write, bool exec) {
 #else  // not COMPILER_MSVC
 #endif  // COMPILER_MSVC
 
-#ifdef COMPILER_MSVC
+static bool IsDirectoryW(const wstring& path) {
+  DWORD attrs = ::GetFileAttributesW(path.c_str());
+  return (attrs != INVALID_FILE_ATTRIBUTES) &&
+         (attrs & FILE_ATTRIBUTE_DIRECTORY) &&
+         JunctionResolver().Resolve(path.c_str(), nullptr);
+}
+
 bool IsDirectory(const string& path) {
-  // TODO(bazel-team): implement this.
-  pdie(255, "blaze_util::IsDirectory is not implemented on Windows");
-  return false;
+  if (path.empty()) {
+    return false;
+  }
+  wstring wpath;
+  if (!AsWindowsPathWithUncPrefix(path, &wpath)) {
+    return false;
+  }
+  return IsDirectoryW(wpath);
 }
-#else  // not COMPILER_MSVC
-#endif  // COMPILER_MSVC
 
 bool IsRootDirectory(const string& path) {
   return IsRootOrAbsolute(path, true);
diff --git a/src/test/cpp/util/file_windows_test.cc b/src/test/cpp/util/file_windows_test.cc
index 1cf49d88c5..5c2f68ee27 100644
--- a/src/test/cpp/util/file_windows_test.cc
+++ b/src/test/cpp/util/file_windows_test.cc
@@ -290,4 +290,40 @@ TEST(FileTest, TestPathExistsWindows) {
   ASSERT_FALSE(PathExists(JoinPath(tmpdir, "junc2")));
 }
 
+TEST(FileTest, TestIsDirectory) {
+  ASSERT_FALSE(IsDirectory(""));
+
+  string tmpdir(GetTestTmpDir());
+  ASSERT_LT(0, tmpdir.size());
+  ASSERT_TRUE(IsDirectory(tmpdir));
+  ASSERT_TRUE(IsDirectory("C:\\"));
+  ASSERT_TRUE(IsDirectory("C:/"));
+  ASSERT_TRUE(IsDirectory("/c"));
+
+  ASSERT_FALSE(IsDirectory("non.existent"));
+  // Create a directory under `tempdir`, verify that IsDirectory reports true.
+  // Call it msys_dir1 so we can also use it as a mock msys root.
+  string dir1(JoinPath(tmpdir, "msys_dir1"));
+  ASSERT_EQ(0, mkdir(dir1.c_str()));
+  ASSERT_TRUE(IsDirectory(dir1));
+
+  // Use dir1 as the mock msys root, verify that IsDirectory works for a MSYS
+  // path.
+  SetEnvironmentVariableA("BAZEL_SH", JoinPath(dir1, "bash.exe").c_str());
+  ResetMsysRootForTesting();
+  ASSERT_TRUE(IsDirectory("/"));
+
+  // Verify that IsDirectory works for a junction.
+  string junc1(JoinPath(tmpdir, "junc1"));
+  RunCommand(string("cmd.exe /C mklink /J \"") + junc1 + "\" \"" + dir1 +
+             "\" >NUL 2>NUL");
+  ASSERT_TRUE(IsDirectory(junc1));
+
+  ASSERT_EQ(0, rmdir(dir1.c_str()));
+  ASSERT_FALSE(IsDirectory(dir1));
+  ASSERT_FALSE(IsDirectory(junc1));
+
+  ASSERT_EQ(0, rmdir(junc1.c_str()));
+}
+
 }  // namespace blaze_util