symlinks: make watchman report symlinks

Summary:
This diff makes Watchman report the proper filemode for symlinks on Windows, which makes `hg status` and other related commands work for the old Python status. Note that some additional changes are still needed to make the new Rust status command work with watchman.

This change also makes `test-symlinks.t` work with watchman on Windows

Reviewed By: quark-zju

Differential Revision: D47451133

fbshipit-source-id: c9f93ea7a2add7684983f92b9daec0846c766f5d

watchman/fs/FileInformation.cpp

@@ -36,11 +36,9 @@ FileInformation::FileInformation(uint32_t dwFileAttributes)
     mode = 0666;
   }
   if (fileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) {
-    // It's a symlink, but to be msvc compatible, we report
-    // this as a file.  Note that a reparse point can also
-    // have FILE_ATTRIBUTE_DIRECTORY set if the symlink was
-    // created with the intention of it appearing as a file.
-    mode |= _S_IFREG;
+    // Report it as a symlink. This is used by source control
+    // to detect symlinks.
+    mode |= S_IFLNK;
   } else if (fileAttributes & FILE_ATTRIBUTE_DIRECTORY) {
     mode |= _S_IFDIR | 0111 /* executable/searchable */;
   } else {

watchman/fs/FileInformation.h

@@ -36,6 +36,7 @@ static_assert(S_IFMT == 0xF000, "The S_IFMT on Windows should be 0xF000");
 #define DT_CHR ((_S_IFCHR) >> 12)
 #define DT_DIR ((_S_IFDIR) >> 12)
 #define DT_REG ((_S_IFREG) >> 12)
+#define S_IFLNK 0xA000
 
 #endif