Make `HasAbslStringify` public.

PiperOrigin-RevId: 565050503
Change-Id: I8f4c463be4ef513a2788745d1b454a7ede489152

8 files changed, 147 insertions, 33 deletions

diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel
index e226a27d..6d0ed698 100644
--- a/absl/strings/BUILD.bazel
+++ b/absl/strings/BUILD.bazel
@@ -70,6 +70,7 @@ cc_library(
         "ascii.h",
         "charconv.h",
         "escaping.h",
+        "has_absl_stringify.h",
         "internal/damerau_levenshtein_distance.h",
         "internal/has_absl_stringify.h",
         "internal/string_constant.h",
@@ -180,6 +181,18 @@ cc_test(
 )
 
 cc_test(
+    name = "has_absl_stringify_test",
+    size = "small",
+    srcs = ["has_absl_stringify_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
     name = "ascii_test",
     size = "small",
     srcs = ["ascii_test.cc"],
diff --git a/absl/strings/CMakeLists.txt b/absl/strings/CMakeLists.txt
index 8bd93271..ebf085db 100644
--- a/absl/strings/CMakeLists.txt
+++ b/absl/strings/CMakeLists.txt
@@ -38,6 +38,7 @@ absl_cc_library(
     "ascii.h"
     "charconv.h"
     "escaping.h"
+    "has_absl_stringify.h"
     "internal/damerau_levenshtein_distance.h"
     "internal/string_constant.h"
     "internal/has_absl_stringify.h"
@@ -156,6 +157,18 @@ absl_cc_test(
 
 absl_cc_test(
   NAME
+    has_absl_stringify_test
+  SRCS
+    "has_absl_stringify_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    GTest::gmock_main
+)
+
+absl_cc_test(
+  NAME
     ascii_test
   SRCS
     "ascii_test.cc"
diff --git a/absl/strings/has_absl_stringify.h b/absl/strings/has_absl_stringify.h
new file mode 100644
index 00000000..274a7865
--- /dev/null
+++ b/absl/strings/has_absl_stringify.h
@@ -0,0 +1,63 @@
+// Copyright 2022 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_
+#define ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_
+
+#include <type_traits>
+#include <utility>
+
+#include "absl/strings/string_view.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace strings_internal {
+
+// This is an empty class not intended to be used. It exists so that
+// `HasAbslStringify` can reference a universal class rather than needing to be
+// copied for each new sink.
+class UnimplementedSink {
+ public:
+  void Append(size_t count, char ch);
+
+  void Append(string_view v);
+
+  // Support `absl::Format(&sink, format, args...)`.
+  friend void AbslFormatFlush(UnimplementedSink* sink, absl::string_view v);
+};
+
+}  // namespace strings_internal
+
+// `HasAbslStringify<T>` detects if type `T` supports the `AbslStringify()`
+// customization point (see
+// https://abseil.io/docs/cpp/guides/format#abslstringify for the
+// documentation).
+//
+// Note that there are types that can be `StrCat`-ed that do not use the
+// `AbslStringify` customization point (for example, `int`).
+
+template <typename T, typename = void>
+struct HasAbslStringify : std::false_type {};
+
+template <typename T>
+struct HasAbslStringify<
+    T, std::enable_if_t<std::is_void<decltype(AbslStringify(
+           std::declval<strings_internal::UnimplementedSink&>(),
+           std::declval<const T&>()))>::value>> : std::true_type {};
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_
diff --git a/absl/strings/has_absl_stringify_test.cc b/absl/strings/has_absl_stringify_test.cc
new file mode 100644
index 00000000..e9915c66
--- /dev/null
+++ b/absl/strings/has_absl_stringify_test.cc
@@ -0,0 +1,37 @@
+// Copyright 2023 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/has_absl_stringify.h"
+
+#include <string>
+
+#include "gtest/gtest.h"
+
+namespace {
+
+struct TypeWithoutAbslStringify {};
+
+struct TypeWithAbslStringify {
+  template <typename Sink>
+  friend void AbslStringify(Sink&, const TypeWithAbslStringify&) {}
+};
+
+TEST(HasAbslStringifyTest, Works) {
+  EXPECT_FALSE(absl::HasAbslStringify<int>::value);
+  EXPECT_FALSE(absl::HasAbslStringify<std::string>::value);
+  EXPECT_FALSE(absl::HasAbslStringify<TypeWithoutAbslStringify>::value);
+  EXPECT_TRUE(absl::HasAbslStringify<TypeWithAbslStringify>::value);
+}
+
+}  // namespace
diff --git a/absl/strings/internal/has_absl_stringify.h b/absl/strings/internal/has_absl_stringify.h
index 55a08508..5eaddad1 100644
--- a/absl/strings/internal/has_absl_stringify.h
+++ b/absl/strings/internal/has_absl_stringify.h
@@ -18,31 +18,20 @@
 #include <type_traits>
 #include <utility>
 
-#include "absl/strings/string_view.h"
+#include "absl/base/attributes.h"
+#include "absl/strings/has_absl_stringify.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 
 namespace strings_internal {
 
-// This is an empty class not intended to be used. It exists so that
-// `HasAbslStringify` can reference a universal class rather than needing to be
-// copied for each new sink.
-class UnimplementedSink {
- public:
-  void Append(size_t count, char ch);
-
-  void Append(string_view v);
-
-  // Support `absl::Format(&sink, format, args...)`.
-  friend void AbslFormatFlush(UnimplementedSink* sink, absl::string_view v);
-};
-
 template <typename T, typename = void>
-struct HasAbslStringify : std::false_type {};
+struct ABSL_DEPRECATED("Use absl::HasAbslStringify") HasAbslStringify
+    : std::false_type {};
 
 template <typename T>
-struct HasAbslStringify<
+struct ABSL_DEPRECATED("Use absl::HasAbslStringify") HasAbslStringify<
     T, std::enable_if_t<std::is_void<decltype(AbslStringify(
            std::declval<strings_internal::UnimplementedSink&>(),
            std::declval<const T&>()))>::value>> : std::true_type {};
diff --git a/absl/strings/internal/str_format/arg.h b/absl/strings/internal/str_format/arg.h
index 3ce30feb..2e017549 100644
--- a/absl/strings/internal/str_format/arg.h
+++ b/absl/strings/internal/str_format/arg.h
@@ -31,7 +31,7 @@
 #include "absl/base/port.h"
 #include "absl/meta/type_traits.h"
 #include "absl/numeric/int128.h"
-#include "absl/strings/internal/has_absl_stringify.h"
+#include "absl/strings/has_absl_stringify.h"
 #include "absl/strings/internal/str_format/extension.h"
 #include "absl/strings/string_view.h"
 
@@ -333,7 +333,7 @@ IntegralConvertResult FormatConvertImpl(T v, FormatConversionSpecImpl conv,
 template <typename T>
 typename std::enable_if<std::is_enum<T>::value &&
                             !HasUserDefinedConvert<T>::value &&
-                            !strings_internal::HasAbslStringify<T>::value,
+                            !HasAbslStringify<T>::value,
                         IntegralConvertResult>::type
 FormatConvertImpl(T v, FormatConversionSpecImpl conv, FormatSinkImpl* sink);
 
@@ -447,7 +447,7 @@ class FormatArgImpl {
   struct DecayType {
     static constexpr bool kHasUserDefined =
         str_format_internal::HasUserDefinedConvert<T>::value ||
-        strings_internal::HasAbslStringify<T>::value;
+        HasAbslStringify<T>::value;
     using type = typename std::conditional<
         !kHasUserDefined && std::is_convertible<T, const char*>::value,
         const char*,
@@ -456,11 +456,10 @@ class FormatArgImpl {
                                   VoidPtr, const T&>::type>::type;
   };
   template <typename T>
-  struct DecayType<T,
-                   typename std::enable_if<
-                       !str_format_internal::HasUserDefinedConvert<T>::value &&
-                       !strings_internal::HasAbslStringify<T>::value &&
-                       std::is_enum<T>::value>::type> {
+  struct DecayType<
+      T, typename std::enable_if<
+             !str_format_internal::HasUserDefinedConvert<T>::value &&
+             !HasAbslStringify<T>::value && std::is_enum<T>::value>::type> {
     using type = decltype(+typename std::underlying_type<T>::type());
   };
 
diff --git a/absl/strings/str_cat.h b/absl/strings/str_cat.h
index 554c89de..e7823683 100644
--- a/absl/strings/str_cat.h
+++ b/absl/strings/str_cat.h
@@ -102,7 +102,7 @@
 #include "absl/base/attributes.h"
 #include "absl/base/port.h"
 #include "absl/meta/type_traits.h"
-#include "absl/strings/internal/has_absl_stringify.h"
+#include "absl/strings/has_absl_stringify.h"
 #include "absl/strings/internal/resize_uninitialized.h"
 #include "absl/strings/internal/stringify_sink.h"
 #include "absl/strings/numbers.h"
@@ -357,7 +357,7 @@ class AlphaNum {
       : piece_(pc) {}
 
   template <typename T, typename = typename std::enable_if<
-                            strings_internal::HasAbslStringify<T>::value>::type>
+                            HasAbslStringify<T>::value>::type>
   AlphaNum(  // NOLINT(runtime/explicit)
       const T& v ABSL_ATTRIBUTE_LIFETIME_BOUND,
       strings_internal::StringifySink&& sink ABSL_ATTRIBUTE_LIFETIME_BOUND = {})
@@ -384,17 +384,17 @@ class AlphaNum {
   template <typename T,
             typename = typename std::enable_if<
                 std::is_enum<T>{} && std::is_convertible<T, int>{} &&
-                !strings_internal::HasAbslStringify<T>::value>::type>
+                !HasAbslStringify<T>::value>::type>
   AlphaNum(T e)  // NOLINT(runtime/explicit)
       : AlphaNum(+e) {}
 
   // This overload matches scoped enums.  We must explicitly cast to the
   // underlying type, but use integral promotion for the same reason as above.
   template <typename T,
-            typename std::enable_if<
-                std::is_enum<T>{} && !std::is_convertible<T, int>{} &&
-                    !strings_internal::HasAbslStringify<T>::value,
-                char*>::type = nullptr>
+            typename std::enable_if<std::is_enum<T>{} &&
+                                        !std::is_convertible<T, int>{} &&
+                                        !HasAbslStringify<T>::value,
+                                    char*>::type = nullptr>
   AlphaNum(T e)  // NOLINT(runtime/explicit)
       : AlphaNum(+static_cast<typename std::underlying_type<T>::type>(e)) {}
 
diff --git a/absl/strings/substitute.h b/absl/strings/substitute.h
index d6a5a690..0d6cb7c7 100644
--- a/absl/strings/substitute.h
+++ b/absl/strings/substitute.h
@@ -176,7 +176,7 @@ class Arg {
       : piece_(value ? "true" : "false") {}
 
   template <typename T, typename = typename std::enable_if<
-                            strings_internal::HasAbslStringify<T>::value>::type>
+                            HasAbslStringify<T>::value>::type>
   Arg(  // NOLINT(google-explicit-constructor)
       const T& v, strings_internal::StringifySink&& sink = {})
       : piece_(strings_internal::ExtractStringification(sink, v)) {}
@@ -204,7 +204,7 @@ class Arg {
   template <typename T,
             typename = typename std::enable_if<
                 std::is_enum<T>{} && !std::is_convertible<T, int>{} &&
-                !strings_internal::HasAbslStringify<T>::value>::type>
+                !HasAbslStringify<T>::value>::type>
   Arg(T value)  // NOLINT(google-explicit-constructor)
       : Arg(static_cast<typename std::underlying_type<T>::type>(value)) {}