Add a formatter for folly::StringPiece

CMakeLists.txt

@@ -148,8 +148,8 @@ function(add_headers VAR)
 endfunction()
 
 # Define the fmt library, its includes and the needed defines.
-add_headers(FMT_HEADERS core.h format.h format-inl.h ostream.h printf.h time.h
-                        ranges.h)
+add_headers(FMT_HEADERS core.h folly.h format.h format-inl.h ostream.h printf.h
+                        time.h ranges.h)
 set(FMT_SOURCES src/format.cc)
 if (HAVE_OPEN)
   add_headers(FMT_HEADERS posix.h)

include/fmt/folly.h

+// Formatting library for C++ - folly::StringPiece formatter
+//
+// Copyright (c) 2012 - present, Victor Zverovich
+// All rights reserved.
+//
+// For the license information refer to format.h.
+
+#ifndef FMT_FOLLY_H_
+#define FMT_FOLLY_H_
+
+#include <folly/Range.h>
+#include "core.h"
+
+FMT_BEGIN_NAMESPACE
+template <typename Ctx>
+inline internal::typed_value<Ctx, internal::string_type>
+    make_value(folly::StringPiece s) {
+  return string_view(s.data(), s.size());
+}
+FMT_END_NAMESPACE
+
+#endif  // FMT_FOLLY_H_

test/CMakeLists.txt

@@ -86,6 +86,7 @@ endfunction()
 
 add_fmt_test(assert-test)
 add_fmt_test(gtest-extra-test)
+add_fmt_test(folly-test)
 add_fmt_test(format-test)
 add_fmt_test(format-impl-test)
 add_fmt_test(ostream-test)

test/folly-test.cc

+// Formatting library for C++ - folly::StringPiece formatter tests
+//
+// Copyright (c) 2012 - present, Victor Zverovich
+// All rights reserved.
+//
+// For the license information refer to format.h.
+
+#include <fmt/folly.h>
+#include "gtest.h"
+
+TEST(FollyTest, FormatStringPiece) {
+  EXPECT_EQ(fmt::format("{}", "foo"), "foo");
+  EXPECT_EQ(fmt::format("{:>5}", "foo"), "  foo");
+}

test/folly/Range.h

+// A folly::StringPiece stub.
+
+#include <cstring>
+
+namespace folly {
+class StringPiece {
+ public:
+  explicit StringPiece(const char *s) : data_(s), size_(std::strlen(s)) {}
+
+  const char* data() const { return "foo"; }
+  size_t size() const { return 3; }
+
+ private:
+  const char *data_;
+  size_t size_;
+};
+}