Export of internal Abseil changes

--
34c0d521b11ed4191ea3e071a864a84e5e5941b7 by Matthew Brown <matthewbr@google.com>:

Release absl::StrFormat custom type extensions
 - Allows StrFormat methods to be extended to accept types which implement
   AbslFormatConvert()
 - NOLINTNEXTLINE(readability-redundant-declaration) used, declarations are
   required in some compilers.

PiperOrigin-RevId: 316963065

--
4d475b5ad02d41057447d722ad35573fc4f48d1f by Evan Brown <ezb@google.com>:

Small fix to previous change: the first overload of insert_iterator_unique wasn't actually being selected. Fix that issue and add tests to verify that it actually works.

Note: couldn't use TestInstanceTracker here because that counts instances (and decrements in destructor) rather than counting all constructor calls.
PiperOrigin-RevId: 316927690
GitOrigin-RevId: 34c0d521b11ed4191ea3e071a864a84e5e5941b7
Change-Id: If8bbb8317b93af4084ac4cc55b752b99b1581b58

1 files changed, 32 insertions, 2 deletions

diff --git a/absl/strings/internal/str_format/arg.h b/absl/strings/internal/str_format/arg.h
index d441e87f..3dbc1526 100644
--- a/absl/strings/internal/str_format/arg.h
+++ b/absl/strings/internal/str_format/arg.h
@@ -25,10 +25,12 @@ class Cord;
 class FormatCountCapture;
 class FormatSink;
 
-namespace str_format_internal {
-
+template <absl::FormatConversionCharSet C>
+struct FormatConvertResult;
 class FormatConversionSpec;
 
+namespace str_format_internal {
+
 template <typename T, typename = void>
 struct HasUserDefinedConvert : std::false_type {};
 
@@ -39,6 +41,22 @@ struct HasUserDefinedConvert<T, void_t<decltype(AbslFormatConvert(
                                     std::declval<FormatSink*>()))>>
     : std::true_type {};
 
+void AbslFormatConvert();  // Stops the lexical name lookup
+template <typename T>
+auto FormatConvertImpl(const T& v, FormatConversionSpecImpl conv,
+                       FormatSinkImpl* sink)
+    -> decltype(AbslFormatConvert(v,
+                                  std::declval<const FormatConversionSpec&>(),
+                                  std::declval<FormatSink*>())) {
+  using FormatConversionSpecT =
+      absl::enable_if_t<sizeof(const T& (*)()) != 0, FormatConversionSpec>;
+  using FormatSinkT =
+      absl::enable_if_t<sizeof(const T& (*)()) != 0, FormatSink>;
+  auto fcs = conv.Wrap<FormatConversionSpecT>();
+  auto fs = sink->Wrap<FormatSinkT>();
+  return AbslFormatConvert(v, fcs, &fs);
+}
+
 template <typename T>
 class StreamedWrapper;
 
@@ -46,6 +64,13 @@ class StreamedWrapper;
 // then convert it, appending to `sink` and return `true`.
 // Otherwise fail and return `false`.
 
+// AbslFormatConvert(v, conv, sink) is intended to be found by ADL on 'v'
+// as an extension mechanism. These FormatConvertImpl functions are the default
+// implementations.
+// The ADL search is augmented via the 'Sink*' parameter, which also
+// serves as a disambiguator to reject possible unintended 'AbslFormatConvert'
+// functions in the namespaces associated with 'v'.
+
 // Raw pointers.
 struct VoidPtr {
   VoidPtr() = default;
@@ -62,6 +87,11 @@ struct ArgConvertResult {
 };
 
 template <FormatConversionCharSet C>
+constexpr FormatConversionCharSet ExtractCharSet(FormatConvertResult<C>) {
+  return C;
+}
+
+template <FormatConversionCharSet C>
 constexpr FormatConversionCharSet ExtractCharSet(ArgConvertResult<C>) {
   return C;
 }