add a fmt formatter for Hash20

Summary: We're migrating to fmt, so add a formatter for Hash20.

Reviewed By: xavierd

Differential Revision: D41104916

fbshipit-source-id: 51ecbd61f1b5ba2fe257cd6ef5835bc9030b1a0a

eden/fs/model/Hash.h

@@ -156,5 +156,13 @@ struct hash<facebook::eden::Hash20> {
     return hash.getHashCode();
   }
 };
-
 } // namespace std
+
+template <>
+struct fmt::formatter<facebook::eden::Hash20> : formatter<string_view> {
+  template <typename Context>
+  auto format(const facebook::eden::Hash20& h, Context& ctx) const {
+    // TODO: Avoid allocation here.
+    return formatter<string_view>::format(h.toString(), ctx);
+  }
+};

eden/fs/model/test/HashTest.cpp

@@ -219,3 +219,10 @@ TEST(Hash20, getHashCode) {
   // using 64 bits of data to contribute to the hash code.
   EXPECT_EQ(folly::Endian::big(0xfaceb00cdeadbeef), testHash.getHashCode());
 }
+
+TEST(Hash20, formatting) {
+  Hash20 h("0123456789abcdeffedcba987654321076543210");
+  EXPECT_EQ(
+      "0123456789abcdeffedcba987654321076543210", folly::to<std::string>(h));
+  EXPECT_EQ("0123456789abcdeffedcba987654321076543210", fmt::to_string(h));
+}

eden/fs/store/hg/HgImporter.cpp

@@ -22,9 +22,7 @@
 #include <folly/lang/Bits.h>
 #include <folly/logging/xlog.h>
 #include <folly/portability/GFlags.h>
-#ifndef _WIN32
 #include <folly/portability/Unistd.h>
-#endif
 
 #include <mutex>