3 files changed, 47 insertions, 5 deletions
diff --git a/absl/strings/internal/str_format/extension_test.cc b/absl/strings/internal/str_format/extension_test.cc
index 4e23fefbd5b0..dc5576b6337e 100644
--- a/absl/strings/internal/str_format/extension_test.cc
+++ b/absl/strings/internal/str_format/extension_test.cc
@@ -19,9 +19,27 @@
 #include <random>
 #include <string>
 
+#include "absl/strings/cord.h"
+#include "gtest/gtest.h"
 #include "absl/strings/str_format.h"
+#include "absl/strings/string_view.h"
 
-#include "gtest/gtest.h"
+namespace my_namespace {
+class UserDefinedType {
+ public:
+  UserDefinedType() = default;
+
+  void Append(absl::string_view str) { value_.append(str.data(), str.size()); }
+  const std::string& Value() const { return value_; }
+
+  friend void AbslFormatFlush(UserDefinedType* x, absl::string_view str) {
+    x->Append(str);
+  }
+
+ private:
+  std::string value_;
+};
+}  // namespace my_namespace
 
 namespace {
 
@@ -63,4 +81,21 @@ TEST(FormatExtensionTest, SinkAppendChars) {
     EXPECT_EQ(actual, expected);
   }
 }
+
+TEST(FormatExtensionTest, CordSink) {
+  absl::Cord c;
+  absl::Format(&c, "There were %04d little %s.", 3, "pigs");
+  EXPECT_EQ(c, "There were 0003 little pigs.");
+  absl::Format(&c, "And %-3llx bad wolf!", 1);
+  EXPECT_EQ(c, "There were 0003 little pigs.And 1   bad wolf!");
+}
+
+TEST(FormatExtensionTest, CustomSink) {
+  my_namespace::UserDefinedType sink;
+  absl::Format(&sink, "There were %04d little %s.", 3, "pigs");
+  EXPECT_EQ("There were 0003 little pigs.", sink.Value());
+  absl::Format(&sink, "And %-3llx bad wolf!", 1);
+  EXPECT_EQ("There were 0003 little pigs.And 1   bad wolf!", sink.Value());
+}
+
 }  // namespace
diff --git a/absl/strings/internal/str_format/output.h b/absl/strings/internal/str_format/output.h
index 28b288b7dde3..c3168d208590 100644
--- a/absl/strings/internal/str_format/output.h
+++ b/absl/strings/internal/str_format/output.h
@@ -91,10 +91,11 @@ inline void AbslFormatFlush(BufferRawSink* sink, string_view v) {
   sink->Write(v);
 }
 
+// This is a SFINAE to get a better compiler error message when the type
+// is not supported.
 template <typename T>
-auto InvokeFlush(T* out, string_view s)
-    -> decltype(str_format_internal::AbslFormatFlush(out, s)) {
-  str_format_internal::AbslFormatFlush(out, s);
+auto InvokeFlush(T* out, string_view s) -> decltype(AbslFormatFlush(out, s)) {
+  AbslFormatFlush(out, s);
 }
 
 }  // namespace str_format_internal
diff --git a/absl/strings/internal/str_format/output_test.cc b/absl/strings/internal/str_format/output_test.cc
index e54e6f70a511..ce2e91a0bbe8 100644
--- a/absl/strings/internal/str_format/output_test.cc
+++ b/absl/strings/internal/str_format/output_test.cc
@@ -19,6 +19,7 @@
 
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
+#include "absl/strings/cord.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
@@ -37,6 +38,12 @@ TEST(InvokeFlush, Stream) {
   EXPECT_EQ(str.str(), "ABCDEF");
 }
 
+TEST(InvokeFlush, Cord) {
+  absl::Cord str("ABC");
+  str_format_internal::InvokeFlush(&str, "DEF");
+  EXPECT_EQ(str, "ABCDEF");
+}
+
 TEST(BufferRawSink, Limits) {
   char buf[16];
   {
@@ -70,4 +77,3 @@ TEST(BufferRawSink, Limits) {
 }  // namespace
 ABSL_NAMESPACE_END
 }  // namespace absl
-