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-rw-r--r--absl/strings/internal/str_format/arg.cc28
-rw-r--r--absl/strings/internal/str_format/arg.h85
-rw-r--r--absl/strings/internal/str_format/bind.h5
-rw-r--r--absl/strings/internal/str_format/checker.h24
-rw-r--r--absl/strings/internal/str_format/extension.h277
-rw-r--r--absl/strings/internal/str_format/extension_test.cc9
-rw-r--r--absl/strings/internal/str_format/float_conversion.cc110
-rw-r--r--absl/strings/internal/str_format/parser.cc10
-rw-r--r--absl/strings/internal/str_format/parser.h12
-rw-r--r--absl/strings/internal/str_format/parser_test.cc27
10 files changed, 359 insertions, 228 deletions
diff --git a/absl/strings/internal/str_format/arg.cc b/absl/strings/internal/str_format/arg.cc
index 12842276a8e0..a112071c43a7 100644
--- a/absl/strings/internal/str_format/arg.cc
+++ b/absl/strings/internal/str_format/arg.cc
@@ -315,7 +315,7 @@ bool ConvertFloatArg(T v, const ConversionSpec conv, FormatSinkImpl *sink) {
 
 inline bool ConvertStringArg(string_view v, const ConversionSpec conv,
                              FormatSinkImpl *sink) {
-  if (conv.conversion_char() != ConversionChar::s) return false;
+  if (conv.conversion_char() != FormatConversionCharInternal::s) return false;
   if (conv.is_basic()) {
     sink->Append(v);
     return true;
@@ -327,22 +327,22 @@ inline bool ConvertStringArg(string_view v, const ConversionSpec conv,
 }  // namespace
 
 // ==================== Strings ====================
-ConvertResult<Conv::s> FormatConvertImpl(const std::string &v,
-                                         const ConversionSpec conv,
-                                         FormatSinkImpl *sink) {
+StringConvertResult FormatConvertImpl(const std::string &v,
+                                      const ConversionSpec conv,
+                                      FormatSinkImpl *sink) {
   return {ConvertStringArg(v, conv, sink)};
 }
 
-ConvertResult<Conv::s> FormatConvertImpl(string_view v,
-                                         const ConversionSpec conv,
-                                         FormatSinkImpl *sink) {
+StringConvertResult FormatConvertImpl(string_view v, const ConversionSpec conv,
+                                      FormatSinkImpl *sink) {
   return {ConvertStringArg(v, conv, sink)};
 }
 
-ConvertResult<Conv::s | Conv::p> FormatConvertImpl(const char *v,
-                                                   const ConversionSpec conv,
-                                                   FormatSinkImpl *sink) {
-  if (conv.conversion_char() == ConversionChar::p)
+ArgConvertResult<FormatConversionCharSetUnion(
+    FormatConversionCharSetInternal::s, FormatConversionCharSetInternal::p)>
+FormatConvertImpl(const char *v, const ConversionSpec conv,
+                  FormatSinkImpl *sink) {
+  if (conv.conversion_char() == FormatConversionCharInternal::p)
     return {FormatConvertImpl(VoidPtr(v), conv, sink).value};
   size_t len;
   if (v == nullptr) {
@@ -357,9 +357,9 @@ ConvertResult<Conv::s | Conv::p> FormatConvertImpl(const char *v,
 }
 
 // ==================== Raw pointers ====================
-ConvertResult<Conv::p> FormatConvertImpl(VoidPtr v, const ConversionSpec conv,
-                                         FormatSinkImpl *sink) {
-  if (conv.conversion_char() != ConversionChar::p) return {false};
+ArgConvertResult<FormatConversionCharSetInternal::p> FormatConvertImpl(
+    VoidPtr v, const ConversionSpec conv, FormatSinkImpl *sink) {
+  if (conv.conversion_char() != FormatConversionCharInternal::p) return {false};
   if (!v.value) {
     sink->Append("(nil)");
     return {true};
diff --git a/absl/strings/internal/str_format/arg.h b/absl/strings/internal/str_format/arg.h
index 1c36e3098c49..f4ac940ab43f 100644
--- a/absl/strings/internal/str_format/arg.h
+++ b/absl/strings/internal/str_format/arg.h
@@ -31,10 +31,11 @@ template <typename T, typename = void>
 struct HasUserDefinedConvert : std::false_type {};
 
 template <typename T>
-struct HasUserDefinedConvert<
-    T, void_t<decltype(AbslFormatConvert(
-           std::declval<const T&>(), std::declval<ConversionSpec>(),
-           std::declval<FormatSink*>()))>> : std::true_type {};
+struct HasUserDefinedConvert<T, void_t<decltype(AbslFormatConvert(
+                                    std::declval<const T&>(),
+                                    std::declval<const FormatConversionSpec&>(),
+                                    std::declval<FormatSink*>()))>>
+    : std::true_type {};
 
 template <typename T>
 class StreamedWrapper;
@@ -52,25 +53,36 @@ struct VoidPtr {
       : value(ptr ? reinterpret_cast<uintptr_t>(ptr) : 0) {}
   uintptr_t value;
 };
-ConvertResult<Conv::p> FormatConvertImpl(VoidPtr v, ConversionSpec conv,
-                                         FormatSinkImpl* sink);
+
+template <FormatConversionCharSet C>
+struct ArgConvertResult {
+  bool value;
+};
+
+template <FormatConversionCharSet C>
+constexpr FormatConversionCharSet ExtractCharSet(ArgConvertResult<C>) {
+  return C;
+}
+
+using StringConvertResult =
+    ArgConvertResult<FormatConversionCharSetInternal::s>;
+ArgConvertResult<FormatConversionCharSetInternal::p> FormatConvertImpl(
+    VoidPtr v, ConversionSpec conv, FormatSinkImpl* sink);
 
 // Strings.
-ConvertResult<Conv::s> FormatConvertImpl(const std::string& v,
-                                         ConversionSpec conv,
-                                         FormatSinkImpl* sink);
-ConvertResult<Conv::s> FormatConvertImpl(string_view v, ConversionSpec conv,
-                                         FormatSinkImpl* sink);
-ConvertResult<Conv::s | Conv::p> FormatConvertImpl(const char* v,
-                                                   ConversionSpec conv,
-                                                   FormatSinkImpl* sink);
-template <class AbslCord,
-          typename std::enable_if<
-              std::is_same<AbslCord, absl::Cord>::value>::type* = nullptr>
-ConvertResult<Conv::s> FormatConvertImpl(const AbslCord& value,
-                                         ConversionSpec conv,
-                                         FormatSinkImpl* sink) {
-  if (conv.conversion_char() != ConversionChar::s) {
+StringConvertResult FormatConvertImpl(const std::string& v, ConversionSpec conv,
+                                      FormatSinkImpl* sink);
+StringConvertResult FormatConvertImpl(string_view v, ConversionSpec conv,
+                                      FormatSinkImpl* sink);
+ArgConvertResult<FormatConversionCharSetUnion(
+    FormatConversionCharSetInternal::s, FormatConversionCharSetInternal::p)>
+FormatConvertImpl(const char* v, ConversionSpec conv, FormatSinkImpl* sink);
+template <class AbslCord, typename std::enable_if<std::is_same<
+                              AbslCord, absl::Cord>::value>::type* = nullptr>
+StringConvertResult FormatConvertImpl(const AbslCord& value,
+                                      ConversionSpec conv,
+                                      FormatSinkImpl* sink) {
+  if (conv.conversion_char() != FormatConversionCharInternal::s) {
     return {false};
   }
 
@@ -107,9 +119,12 @@ ConvertResult<Conv::s> FormatConvertImpl(const AbslCord& value,
   return {true};
 }
 
-using IntegralConvertResult =
-    ConvertResult<Conv::c | Conv::kNumeric | Conv::kStar>;
-using FloatingConvertResult = ConvertResult<Conv::kFloating>;
+using IntegralConvertResult = ArgConvertResult<FormatConversionCharSetUnion(
+    FormatConversionCharSetInternal::c,
+    FormatConversionCharSetInternal::kNumeric,
+    FormatConversionCharSetInternal::kStar)>;
+using FloatingConvertResult =
+    ArgConvertResult<FormatConversionCharSetInternal::kFloating>;
 
 // Floats.
 FloatingConvertResult FormatConvertImpl(float v, ConversionSpec conv,
@@ -169,9 +184,9 @@ typename std::enable_if<std::is_enum<T>::value &&
 FormatConvertImpl(T v, ConversionSpec conv, FormatSinkImpl* sink);
 
 template <typename T>
-ConvertResult<Conv::s> FormatConvertImpl(const StreamedWrapper<T>& v,
-                                         ConversionSpec conv,
-                                         FormatSinkImpl* out) {
+StringConvertResult FormatConvertImpl(const StreamedWrapper<T>& v,
+                                      ConversionSpec conv,
+                                      FormatSinkImpl* out) {
   std::ostringstream oss;
   oss << v.v_;
   if (!oss) return {false};
@@ -182,12 +197,12 @@ ConvertResult<Conv::s> FormatConvertImpl(const StreamedWrapper<T>& v,
 // until after FormatCountCapture is fully defined.
 struct FormatCountCaptureHelper {
   template <class T = int>
-  static ConvertResult<Conv::n> ConvertHelper(const FormatCountCapture& v,
-                                              ConversionSpec conv,
-                                              FormatSinkImpl* sink) {
+  static ArgConvertResult<FormatConversionCharSetInternal::n> ConvertHelper(
+      const FormatCountCapture& v, ConversionSpec conv, FormatSinkImpl* sink) {
     const absl::enable_if_t<sizeof(T) != 0, FormatCountCapture>& v2 = v;
 
-    if (conv.conversion_char() != str_format_internal::ConversionChar::n) {
+    if (conv.conversion_char() !=
+        str_format_internal::FormatConversionCharInternal::n) {
       return {false};
     }
     *v2.p_ = static_cast<int>(sink->size());
@@ -196,9 +211,8 @@ struct FormatCountCaptureHelper {
 };
 
 template <class T = int>
-ConvertResult<Conv::n> FormatConvertImpl(const FormatCountCapture& v,
-                                         ConversionSpec conv,
-                                         FormatSinkImpl* sink) {
+ArgConvertResult<FormatConversionCharSetInternal::n> FormatConvertImpl(
+    const FormatCountCapture& v, ConversionSpec conv, FormatSinkImpl* sink) {
   return FormatCountCaptureHelper::ConvertHelper(v, conv, sink);
 }
 
@@ -381,7 +395,8 @@ class FormatArgImpl {
   template <typename T>
   static bool Dispatch(Data arg, ConversionSpec spec, void* out) {
     // A `none` conv indicates that we want the `int` conversion.
-    if (ABSL_PREDICT_FALSE(spec.conversion_char() == ConversionChar::kNone)) {
+    if (ABSL_PREDICT_FALSE(spec.conversion_char() ==
+                           FormatConversionCharInternal::kNone)) {
       return ToInt<T>(arg, static_cast<int*>(out), std::is_integral<T>(),
                       std::is_enum<T>());
     }
diff --git a/absl/strings/internal/str_format/bind.h b/absl/strings/internal/str_format/bind.h
index d30fdf5078d4..05105d8d5c9c 100644
--- a/absl/strings/internal/str_format/bind.h
+++ b/absl/strings/internal/str_format/bind.h
@@ -189,9 +189,8 @@ class StreamedWrapper {
 
  private:
   template <typename S>
-  friend ConvertResult<Conv::s> FormatConvertImpl(const StreamedWrapper<S>& v,
-                                                  ConversionSpec conv,
-                                                  FormatSinkImpl* out);
+  friend ArgConvertResult<FormatConversionCharSetInternal::s> FormatConvertImpl(
+      const StreamedWrapper<S>& v, ConversionSpec conv, FormatSinkImpl* out);
   const T& v_;
 };
 
diff --git a/absl/strings/internal/str_format/checker.h b/absl/strings/internal/str_format/checker.h
index 8993a79b9580..73ef05ff44b3 100644
--- a/absl/strings/internal/str_format/checker.h
+++ b/absl/strings/internal/str_format/checker.h
@@ -25,10 +25,12 @@ constexpr bool AllOf(bool b, T... t) {
 }
 
 template <typename Arg>
-constexpr Conv ArgumentToConv() {
-  return decltype(str_format_internal::FormatConvertImpl(
-      std::declval<const Arg&>(), std::declval<const ConversionSpec&>(),
-      std::declval<FormatSinkImpl*>()))::kConv;
+constexpr FormatConversionCharSet ArgumentToConv() {
+  return absl::str_format_internal::ExtractCharSet(
+      decltype(str_format_internal::FormatConvertImpl(
+          std::declval<const Arg&>(),
+          std::declval<const FormatConversionSpecImpl&>(),
+          std::declval<FormatSinkImpl*>())){});
 }
 
 #ifdef ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
@@ -39,14 +41,14 @@ constexpr bool ContainsChar(const char* chars, char c) {
 
 // A constexpr compatible list of Convs.
 struct ConvList {
-  const Conv* array;
+  const FormatConversionCharSet* array;
   int count;
 
   // We do the bound check here to avoid having to do it on the callers.
-  // Returning an empty Conv has the same effect as short circuiting because it
-  // will never match any conversion.
-  constexpr Conv operator[](int i) const {
-    return i < count ? array[i] : Conv{};
+  // Returning an empty FormatConversionCharSet has the same effect as
+  // short circuiting because it will never match any conversion.
+  constexpr FormatConversionCharSet operator[](int i) const {
+    return i < count ? array[i] : FormatConversionCharSet{};
   }
 
   constexpr ConvList without_front() const {
@@ -57,7 +59,7 @@ struct ConvList {
 template <size_t count>
 struct ConvListT {
   // Make sure the array has size > 0.
-  Conv list[count ? count : 1];
+  FormatConversionCharSet list[count ? count : 1];
 };
 
 constexpr char GetChar(string_view str, size_t index) {
@@ -310,7 +312,7 @@ class FormatParser {
   ConvList args_;
 };
 
-template <Conv... C>
+template <FormatConversionCharSet... C>
 constexpr bool ValidFormatImpl(string_view format) {
   return FormatParser(format,
                       {ConvListT<sizeof...(C)>{{C...}}.list, sizeof...(C)})
diff --git a/absl/strings/internal/str_format/extension.h b/absl/strings/internal/str_format/extension.h
index fb31a9db415e..f0cffe1e6d6c 100644
--- a/absl/strings/internal/str_format/extension.h
+++ b/absl/strings/internal/str_format/extension.h
@@ -30,7 +30,10 @@
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
+
 namespace str_format_internal {
+enum class FormatConversionCharSet : uint64_t;
+enum class FormatConversionChar : uint8_t;
 
 class FormatRawSinkImpl {
  public:
@@ -149,13 +152,39 @@ struct Flags {
   X_VAL(g) X_SEP X_VAL(G) X_SEP X_VAL(a) X_SEP X_VAL(A) X_SEP \
   /* misc */ \
   X_VAL(n) X_SEP X_VAL(p)
+// clang-format on
 
-enum class FormatConversionChar : uint8_t {
+// This type should not be referenced, it exists only to provide labels
+// internally that match the values declared in FormatConversionChar in
+// str_format.h. This is meant to allow internal libraries to use the same
+// declared interface type as the public interface
+// (absl::StrFormatConversionChar) while keeping the definition in a public
+// header.
+// Internal libraries should use the form
+// `FormatConversionCharInternal::c`, `FormatConversionCharInternal::kNone` for
+// comparisons.  Use in switch statements is not recommended due to a bug in how
+// gcc 4.9 -Wswitch handles declared but undefined enums.
+struct FormatConversionCharInternal {
+  FormatConversionCharInternal() = delete;
+
+ private:
+  // clang-format off
+  enum class Enum : uint8_t {
     c, C, s, S,              // text
     d, i, o, u, x, X,        // int
     f, F, e, E, g, G, a, A,  // float
     n, p,                    // misc
     kNone
+  };
+  // clang-format on
+ public:
+#define ABSL_INTERNAL_X_VAL(id)              \
+  static constexpr FormatConversionChar id = \
+      static_cast<FormatConversionChar>(Enum::id);
+  ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_X_VAL, )
+#undef ABSL_INTERNAL_X_VAL
+  static constexpr FormatConversionChar kNone =
+      static_cast<FormatConversionChar>(Enum::kNone);
 };
 // clang-format on
 
@@ -163,56 +192,56 @@ inline FormatConversionChar FormatConversionCharFromChar(char c) {
   switch (c) {
 #define ABSL_INTERNAL_X_VAL(id) \
   case #id[0]:                  \
-    return FormatConversionChar::id;
+    return FormatConversionCharInternal::id;
     ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_X_VAL, )
 #undef ABSL_INTERNAL_X_VAL
   }
-  return FormatConversionChar::kNone;
+  return FormatConversionCharInternal::kNone;
 }
 
 inline bool FormatConversionCharIsUpper(FormatConversionChar c) {
-  switch (c) {
-    case FormatConversionChar::X:
-    case FormatConversionChar::F:
-    case FormatConversionChar::E:
-    case FormatConversionChar::G:
-    case FormatConversionChar::A:
-      return true;
-    default:
-      return false;
+  if (c == FormatConversionCharInternal::X ||
+      c == FormatConversionCharInternal::F ||
+      c == FormatConversionCharInternal::E ||
+      c == FormatConversionCharInternal::G ||
+      c == FormatConversionCharInternal::A) {
+    return true;
+  } else {
+    return false;
   }
 }
 
 inline bool FormatConversionCharIsFloat(FormatConversionChar c) {
-  switch (c) {
-    case FormatConversionChar::a:
-    case FormatConversionChar::e:
-    case FormatConversionChar::f:
-    case FormatConversionChar::g:
-    case FormatConversionChar::A:
-    case FormatConversionChar::E:
-    case FormatConversionChar::F:
-    case FormatConversionChar::G:
-      return true;
-    default:
-      return false;
+  if (c == FormatConversionCharInternal::a ||
+      c == FormatConversionCharInternal::e ||
+      c == FormatConversionCharInternal::f ||
+      c == FormatConversionCharInternal::g ||
+      c == FormatConversionCharInternal::A ||
+      c == FormatConversionCharInternal::E ||
+      c == FormatConversionCharInternal::F ||
+      c == FormatConversionCharInternal::G) {
+    return true;
+  } else {
+    return false;
   }
 }
 
 inline char FormatConversionCharToChar(FormatConversionChar c) {
-  switch (c) {
-#define ABSL_INTERNAL_X_VAL(e)  \
-  case FormatConversionChar::e: \
+  if (c == FormatConversionCharInternal::kNone) {
+    return '\0';
+
+#define ABSL_INTERNAL_X_VAL(e)                       \
+  } else if (c == FormatConversionCharInternal::e) { \
     return #e[0];
 #define ABSL_INTERNAL_X_SEP
-    ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_X_VAL,
-                                           ABSL_INTERNAL_X_SEP)
-    case FormatConversionChar::kNone:
-      return '\0';
+  ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_X_VAL,
+                                         ABSL_INTERNAL_X_SEP)
+  } else {
+    return '\0';
+  }
+
 #undef ABSL_INTERNAL_X_VAL
 #undef ABSL_INTERNAL_X_SEP
-  }
-  return '\0';
 }
 
 // The associated char.
@@ -224,7 +253,7 @@ inline std::ostream& operator<<(std::ostream& os, FormatConversionChar v) {
 
 struct FormatConversionSpecImplFriend;
 
-class FormatConversionSpec {
+class FormatConversionSpecImpl {
  public:
   // Width and precison are not specified, no flags are set.
   bool is_basic() const { return flags_.basic; }
@@ -237,7 +266,7 @@ class FormatConversionSpec {
   FormatConversionChar conversion_char() const {
     // Keep this field first in the struct . It generates better code when
     // accessing it when ConversionSpec is passed by value in registers.
-    static_assert(offsetof(FormatConversionSpec, conv_) == 0, "");
+    static_assert(offsetof(FormatConversionSpecImpl, conv_) == 0, "");
     return conv_;
   }
 
@@ -248,37 +277,62 @@ class FormatConversionSpec {
   // negative value.
   int precision() const { return precision_; }
 
+  template <typename T>
+  T Wrap() {
+    return T(*this);
+  }
+
  private:
   friend struct str_format_internal::FormatConversionSpecImplFriend;
-  FormatConversionChar conv_ = FormatConversionChar::kNone;
+  FormatConversionChar conv_ = FormatConversionCharInternal::kNone;
   Flags flags_;
   int width_;
   int precision_;
 };
 
 struct FormatConversionSpecImplFriend final {
-  static void SetFlags(Flags f, FormatConversionSpec* conv) {
+  static void SetFlags(Flags f, FormatConversionSpecImpl* conv) {
     conv->flags_ = f;
   }
   static void SetConversionChar(FormatConversionChar c,
-                                FormatConversionSpec* conv) {
+                                FormatConversionSpecImpl* conv) {
     conv->conv_ = c;
   }
-  static void SetWidth(int w, FormatConversionSpec* conv) { conv->width_ = w; }
-  static void SetPrecision(int p, FormatConversionSpec* conv) {
+  static void SetWidth(int w, FormatConversionSpecImpl* conv) {
+    conv->width_ = w;
+  }
+  static void SetPrecision(int p, FormatConversionSpecImpl* conv) {
     conv->precision_ = p;
   }
-  static std::string FlagsToString(const FormatConversionSpec& spec) {
+  static std::string FlagsToString(const FormatConversionSpecImpl& spec) {
     return spec.flags_.ToString();
   }
 };
 
-constexpr uint64_t FormatConversionCharToConvValue(char conv) {
+// Type safe OR operator.
+// We need this for two reasons:
+//  1. operator| on enums makes them decay to integers and the result is an
+//     integer. We need the result to stay as an enum.
+//  2. We use "enum class" which would not work even if we accepted the decay.
+constexpr FormatConversionCharSet FormatConversionCharSetUnion(
+    FormatConversionCharSet a) {
+  return a;
+}
+
+template <typename... CharSet>
+constexpr FormatConversionCharSet FormatConversionCharSetUnion(
+    FormatConversionCharSet a, CharSet... rest) {
+  return static_cast<FormatConversionCharSet>(
+      static_cast<uint64_t>(a) |
+      static_cast<uint64_t>(FormatConversionCharSetUnion(rest...)));
+}
+
+constexpr uint64_t FormatConversionCharToConvInt(char conv) {
   return
-#define ABSL_INTERNAL_CHAR_SET_CASE(c)                                       \
-  conv == #c[0]                                                              \
-      ? (uint64_t{1} << (1 + static_cast<uint8_t>(FormatConversionChar::c))) \
-      :
+#define ABSL_INTERNAL_CHAR_SET_CASE(c)                                        \
+  conv == #c[0] ? (uint64_t{1} << (1 + static_cast<uint8_t>(                  \
+                                           FormatConversionCharInternal::c))) \
+                :
       ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_CHAR_SET_CASE, )
 #undef ABSL_INTERNAL_CHAR_SET_CASE
                   conv == '*'
@@ -286,20 +340,31 @@ constexpr uint64_t FormatConversionCharToConvValue(char conv) {
           : 0;
 }
 
-enum class FormatConversionCharSet : uint64_t {
-#define ABSL_INTERNAL_CHAR_SET_CASE(c) \
-  c = FormatConversionCharToConvValue(#c[0]),
+constexpr FormatConversionCharSet FormatConversionCharToConvValue(char conv) {
+  return static_cast<FormatConversionCharSet>(
+      FormatConversionCharToConvInt(conv));
+}
+
+struct FormatConversionCharSetInternal {
+#define ABSL_INTERNAL_CHAR_SET_CASE(c)         \
+  static constexpr FormatConversionCharSet c = \
+      FormatConversionCharToConvValue(#c[0]);
   ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_CHAR_SET_CASE, )
 #undef ABSL_INTERNAL_CHAR_SET_CASE
 
   // Used for width/precision '*' specification.
-  kStar = FormatConversionCharToConvValue('*'),
-  // Some predefined values:
-  kIntegral = d | i | u | o | x | X,
-  kFloating = a | e | f | g | A | E | F | G,
-  kNumeric = kIntegral | kFloating,
-  kString = s,
-  kPointer = p
+  static constexpr FormatConversionCharSet kStar =
+      FormatConversionCharToConvValue('*');
+
+  // Some predefined values (TODO(matthewbr), delete any that are unused).
+  static constexpr FormatConversionCharSet kIntegral =
+      FormatConversionCharSetUnion(d, i, u, o, x, X);
+  static constexpr FormatConversionCharSet kFloating =
+      FormatConversionCharSetUnion(a, e, f, g, A, E, F, G);
+  static constexpr FormatConversionCharSet kNumeric =
+      FormatConversionCharSetUnion(kIntegral, kFloating);
+  static constexpr FormatConversionCharSet kString = s;
+  static constexpr FormatConversionCharSet kPointer = p;
 };
 
 // Type safe OR operator.
@@ -309,8 +374,7 @@ enum class FormatConversionCharSet : uint64_t {
 //  2. We use "enum class" which would not work even if we accepted the decay.
 constexpr FormatConversionCharSet operator|(FormatConversionCharSet a,
                                             FormatConversionCharSet b) {
-  return FormatConversionCharSet(static_cast<uint64_t>(a) |
-                                 static_cast<uint64_t>(b));
+  return FormatConversionCharSetUnion(a, b);
 }
 
 // Overloaded conversion functions to support absl::ParsedFormat.
@@ -331,7 +395,8 @@ void ToFormatConversionCharSet(T) = delete;
 
 // Checks whether `c` exists in `set`.
 constexpr bool Contains(FormatConversionCharSet set, char c) {
-  return (static_cast<uint64_t>(set) & FormatConversionCharToConvValue(c)) != 0;
+  return (static_cast<uint64_t>(set) &
+          static_cast<uint64_t>(FormatConversionCharToConvValue(c))) != 0;
 }
 
 // Checks whether all the characters in `c` are contained in `set`
@@ -341,19 +406,6 @@ constexpr bool Contains(FormatConversionCharSet set,
          static_cast<uint64_t>(c);
 }
 
-// Return type of the AbslFormatConvert() functions.
-// The FormatConversionCharSet template parameter is used to inform the
-// framework of what conversion characters are supported by that
-// AbslFormatConvert routine.
-template <FormatConversionCharSet C>
-struct FormatConvertResult {
-  static constexpr FormatConversionCharSet kConv = C;
-  bool value;
-};
-
-template <FormatConversionCharSet C>
-constexpr FormatConversionCharSet FormatConvertResult<C>::kConv;
-
 // Return capacity - used, clipped to a minimum of 0.
 inline size_t Excess(size_t used, size_t capacity) {
   return used < capacity ? capacity - used : 0;
@@ -361,10 +413,85 @@ inline size_t Excess(size_t used, size_t capacity) {
 
 // Type alias for use during migration.
 using ConversionChar = FormatConversionChar;
-using ConversionSpec = FormatConversionSpec;
+using ConversionSpec = FormatConversionSpecImpl;
 using Conv = FormatConversionCharSet;
-template <FormatConversionCharSet C>
-using ConvertResult = FormatConvertResult<C>;
+
+class FormatConversionSpec {
+ public:
+  // Width and precison are not specified, no flags are set.
+  bool is_basic() const { return impl_.is_basic(); }
+  bool has_left_flag() const { return impl_.has_left_flag(); }
+  bool has_show_pos_flag() const { return impl_.has_show_pos_flag(); }
+  bool has_sign_col_flag() const { return impl_.has_sign_col_flag(); }
+  bool has_alt_flag() const { return impl_.has_alt_flag(); }
+  bool has_zero_flag() const { return impl_.has_zero_flag(); }
+
+  FormatConversionChar conversion_char() const {
+    return impl_.conversion_char();
+  }
+
+  // Returns the specified width. If width is unspecfied, it returns a negative
+  // value.
+  int width() const { return impl_.width(); }
+  // Returns the specified precision. If precision is unspecfied, it returns a
+  // negative value.
+  int precision() const { return impl_.precision(); }
+
+ private:
+  explicit FormatConversionSpec(
+      str_format_internal::FormatConversionSpecImpl impl)
+      : impl_(impl) {}
+
+  friend str_format_internal::FormatConversionSpecImpl;
+
+  absl::str_format_internal::FormatConversionSpecImpl impl_;
+};
+
+// clang-format off
+enum class FormatConversionChar : uint8_t {
+  c, C, s, S,              // text
+  d, i, o, u, x, X,        // int
+  f, F, e, E, g, G, a, A,  // float
+  n, p                     // misc
+};
+// clang-format on
+
+enum class FormatConversionCharSet : uint64_t {
+  // text
+  c = str_format_internal::FormatConversionCharToConvInt('c'),
+  C = str_format_internal::FormatConversionCharToConvInt('C'),
+  s = str_format_internal::FormatConversionCharToConvInt('s'),
+  S = str_format_internal::FormatConversionCharToConvInt('S'),
+  // integer
+  d = str_format_internal::FormatConversionCharToConvInt('d'),
+  i = str_format_internal::FormatConversionCharToConvInt('i'),
+  o = str_format_internal::FormatConversionCharToConvInt('o'),
+  u = str_format_internal::FormatConversionCharToConvInt('u'),
+  x = str_format_internal::FormatConversionCharToConvInt('x'),
+  X = str_format_internal::FormatConversionCharToConvInt('X'),
+  // Float
+  f = str_format_internal::FormatConversionCharToConvInt('f'),
+  F = str_format_internal::FormatConversionCharToConvInt('F'),
+  e = str_format_internal::FormatConversionCharToConvInt('e'),
+  E = str_format_internal::FormatConversionCharToConvInt('E'),
+  g = str_format_internal::FormatConversionCharToConvInt('g'),
+  G = str_format_internal::FormatConversionCharToConvInt('G'),
+  a = str_format_internal::FormatConversionCharToConvInt('a'),
+  A = str_format_internal::FormatConversionCharToConvInt('A'),
+  // misc
+  n = str_format_internal::FormatConversionCharToConvInt('n'),
+  p = str_format_internal::FormatConversionCharToConvInt('p'),
+
+  // Used for width/precision '*' specification.
+  kStar = str_format_internal::FormatConversionCharToConvInt('*'),
+
+  // Some predefined values:
+  kIntegral = d | i | u | o | x | X,
+  kFloating = a | e | f | g | A | E | F | G,
+  kNumeric = kIntegral | kFloating,
+  kString = s,
+  kPointer = p,
+};
 
 }  // namespace str_format_internal
 
diff --git a/absl/strings/internal/str_format/extension_test.cc b/absl/strings/internal/str_format/extension_test.cc
index 561eaa36b845..0a023f9c0333 100644
--- a/absl/strings/internal/str_format/extension_test.cc
+++ b/absl/strings/internal/str_format/extension_test.cc
@@ -80,13 +80,4 @@ TEST(FormatExtensionTest, SinkAppendChars) {
     EXPECT_EQ(actual, expected);
   }
 }
-
-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/float_conversion.cc b/absl/strings/internal/str_format/float_conversion.cc
index d5a1ee40bc67..d6858cfffd95 100644
--- a/absl/strings/internal/str_format/float_conversion.cc
+++ b/absl/strings/internal/str_format/float_conversion.cc
@@ -403,70 +403,62 @@ bool FloatToSink(const Float v, const ConversionSpec &conv,
 
   Buffer buffer;
 
-  switch (conv.conversion_char()) {
-    case ConversionChar::f:
-    case ConversionChar::F:
-      if (!FloatToBuffer<FormatStyle::Fixed>(decomposed, precision, &buffer,
-                                             nullptr)) {
-        return FallbackToSnprintf(v, conv, sink);
-      }
-      if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back();
-      break;
+  FormatConversionChar c = conv.conversion_char();
 
-    case ConversionChar::e:
-    case ConversionChar::E:
-      if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
-                                                 &exp)) {
-        return FallbackToSnprintf(v, conv, sink);
+  if (c == FormatConversionCharInternal::f ||
+      c == FormatConversionCharInternal::F) {
+    if (!FloatToBuffer<FormatStyle::Fixed>(decomposed, precision, &buffer,
+                                           nullptr)) {
+      return FallbackToSnprintf(v, conv, sink);
+    }
+    if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back();
+  } else if (c == FormatConversionCharInternal::e ||
+             c == FormatConversionCharInternal::E) {
+    if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
+                                               &exp)) {
+      return FallbackToSnprintf(v, conv, sink);
+    }
+    if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back();
+    PrintExponent(
+        exp, FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e',
+        &buffer);
+  } else if (c == FormatConversionCharInternal::g ||
+             c == FormatConversionCharInternal::G) {
+    precision = std::max(0, precision - 1);
+    if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
+                                               &exp)) {
+      return FallbackToSnprintf(v, conv, sink);
+    }
+    if (precision + 1 > exp && exp >= -4) {
+      if (exp < 0) {
+        // Have 1.23456, needs 0.00123456
+        // Move the first digit
+        buffer.begin[1] = *buffer.begin;
+        // Add some zeros
+        for (; exp < -1; ++exp) *buffer.begin-- = '0';
+        *buffer.begin-- = '.';
+        *buffer.begin = '0';
+      } else if (exp > 0) {
+        // Have 1.23456, needs 1234.56
+        // Move the '.' exp positions to the right.
+        std::rotate(buffer.begin + 1, buffer.begin + 2, buffer.begin + exp + 2);
       }
-      if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back();
+      exp = 0;
+    }
+    if (!conv.has_alt_flag()) {
+      while (buffer.back() == '0') buffer.pop_back();
+      if (buffer.back() == '.') buffer.pop_back();
+    }
+    if (exp) {
       PrintExponent(
           exp, FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e',
           &buffer);
-      break;
-
-    case ConversionChar::g:
-    case ConversionChar::G:
-      precision = std::max(0, precision - 1);
-      if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
-                                                 &exp)) {
-        return FallbackToSnprintf(v, conv, sink);
-      }
-      if (precision + 1 > exp && exp >= -4) {
-        if (exp < 0) {
-          // Have 1.23456, needs 0.00123456
-          // Move the first digit
-          buffer.begin[1] = *buffer.begin;
-          // Add some zeros
-          for (; exp < -1; ++exp) *buffer.begin-- = '0';
-          *buffer.begin-- = '.';
-          *buffer.begin = '0';
-        } else if (exp > 0) {
-          // Have 1.23456, needs 1234.56
-          // Move the '.' exp positions to the right.
-          std::rotate(buffer.begin + 1, buffer.begin + 2,
-                      buffer.begin + exp + 2);
-        }
-        exp = 0;
-      }
-      if (!conv.has_alt_flag()) {
-        while (buffer.back() == '0') buffer.pop_back();
-        if (buffer.back() == '.') buffer.pop_back();
-      }
-      if (exp) {
-        PrintExponent(
-            exp,
-            FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e',
-            &buffer);
-      }
-      break;
-
-    case ConversionChar::a:
-    case ConversionChar::A:
-      return FallbackToSnprintf(v, conv, sink);
-
-    default:
-      return false;
+    }
+  } else if (c == FormatConversionCharInternal::a ||
+             c == FormatConversionCharInternal::A) {
+    return FallbackToSnprintf(v, conv, sink);
+  } else {
+    return false;
   }
 
   WriteBufferToSink(sign_char,
diff --git a/absl/strings/internal/str_format/parser.cc b/absl/strings/internal/str_format/parser.cc
index aab68db94bca..61132739b875 100644
--- a/absl/strings/internal/str_format/parser.cc
+++ b/absl/strings/internal/str_format/parser.cc
@@ -17,7 +17,7 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace str_format_internal {
 
-using CC = ConversionChar;
+using CC = FormatConversionCharInternal;
 using LM = LengthMod;
 
 ABSL_CONST_INIT const ConvTag kTags[256] = {
@@ -296,15 +296,17 @@ struct ParsedFormatBase::ParsedFormatConsumer {
   char* data_pos;
 };
 
-ParsedFormatBase::ParsedFormatBase(string_view format, bool allow_ignored,
-                                   std::initializer_list<Conv> convs)
+ParsedFormatBase::ParsedFormatBase(
+    string_view format, bool allow_ignored,
+    std::initializer_list<FormatConversionCharSet> convs)
     : data_(format.empty() ? nullptr : new char[format.size()]) {
   has_error_ = !ParseFormatString(format, ParsedFormatConsumer(this)) ||
                !MatchesConversions(allow_ignored, convs);
 }
 
 bool ParsedFormatBase::MatchesConversions(
-    bool allow_ignored, std::initializer_list<Conv> convs) const {
+    bool allow_ignored,
+    std::initializer_list<FormatConversionCharSet> convs) const {
   std::unordered_set<int> used;
   auto add_if_valid_conv = [&](int pos, char c) {
       if (static_cast<size_t>(pos) > convs.size() ||
diff --git a/absl/strings/internal/str_format/parser.h b/absl/strings/internal/str_format/parser.h
index 7d966517256b..fd2dc9704507 100644
--- a/absl/strings/internal/str_format/parser.h
+++ b/absl/strings/internal/str_format/parser.h
@@ -67,7 +67,7 @@ struct UnboundConversion {
 
   Flags flags;
   LengthMod length_mod = LengthMod::none;
-  ConversionChar conv = FormatConversionChar::kNone;
+  FormatConversionChar conv = FormatConversionCharInternal::kNone;
 };
 
 // Consume conversion spec prefix (not including '%') of [p, end) if valid.
@@ -186,8 +186,9 @@ constexpr bool EnsureConstexpr(string_view s) {
 
 class ParsedFormatBase {
  public:
-  explicit ParsedFormatBase(string_view format, bool allow_ignored,
-                            std::initializer_list<Conv> convs);
+  explicit ParsedFormatBase(
+      string_view format, bool allow_ignored,
+      std::initializer_list<FormatConversionCharSet> convs);
 
   ParsedFormatBase(const ParsedFormatBase& other) { *this = other; }
 
@@ -234,8 +235,9 @@ class ParsedFormatBase {
  private:
   // Returns whether the conversions match and if !allow_ignored it verifies
   // that all conversions are used by the format.
-  bool MatchesConversions(bool allow_ignored,
-                          std::initializer_list<Conv> convs) const;
+  bool MatchesConversions(
+      bool allow_ignored,
+      std::initializer_list<FormatConversionCharSet> convs) const;
 
   struct ParsedFormatConsumer;
 
diff --git a/absl/strings/internal/str_format/parser_test.cc b/absl/strings/internal/str_format/parser_test.cc
index 51eb53f5a4cf..26f5bec6bcff 100644
--- a/absl/strings/internal/str_format/parser_test.cc
+++ b/absl/strings/internal/str_format/parser_test.cc
@@ -46,13 +46,13 @@ TEST(ConversionCharTest, Names) {
   };
   // clang-format off
   const Expectation kExpect[] = {
-#define X(c) {ConversionChar::c, #c[0]}
+#define X(c) {FormatConversionCharInternal::c, #c[0]}
     X(c), X(C), X(s), X(S),                          // text
     X(d), X(i), X(o), X(u), X(x), X(X),              // int
     X(f), X(F), X(e), X(E), X(g), X(G), X(a), X(A),  // float
     X(n), X(p),                                      // misc
 #undef X
-    {ConversionChar::kNone, '\0'},
+    {FormatConversionCharInternal::kNone, '\0'},
   };
   // clang-format on
   for (auto e : kExpect) {
@@ -349,7 +349,8 @@ TEST_F(ParsedFormatTest, ValueSemantics) {
   ParsedFormatBase p2 = p1;  // copy construct (empty)
   EXPECT_EQ(SummarizeParsedFormat(p1), SummarizeParsedFormat(p2));
 
-  p1 = ParsedFormatBase("hello%s", true, {Conv::s});  // move assign
+  p1 = ParsedFormatBase("hello%s", true,
+                        {FormatConversionCharSetInternal::s});  // move assign
   EXPECT_EQ("[hello]{s:1$s}", SummarizeParsedFormat(p1));
 
   ParsedFormatBase p3 = p1;  // copy construct (nonempty)
@@ -377,9 +378,9 @@ TEST_F(ParsedFormatTest, Parsing) {
   const ExpectParse kExpect[] = {
       {"", {}, ""},
       {"ab", {}, "[ab]"},
-      {"a%d", {Conv::d}, "[a]{d:1$d}"},
-      {"a%+d", {Conv::d}, "[a]{+d:1$d}"},
-      {"a% d", {Conv::d}, "[a]{ d:1$d}"},
+      {"a%d", {FormatConversionCharSetInternal::d}, "[a]{d:1$d}"},
+      {"a%+d", {FormatConversionCharSetInternal::d}, "[a]{+d:1$d}"},
+      {"a% d", {FormatConversionCharSetInternal::d}, "[a]{ d:1$d}"},
       {"a%b %d", {}, "[a]!"},  // stop after error
   };
   for (const auto& e : kExpect) {
@@ -391,13 +392,13 @@ TEST_F(ParsedFormatTest, Parsing) {
 
 TEST_F(ParsedFormatTest, ParsingFlagOrder) {
   const ExpectParse kExpect[] = {
-      {"a%+ 0d", {Conv::d}, "[a]{+ 0d:1$d}"},
-      {"a%+0 d", {Conv::d}, "[a]{+0 d:1$d}"},
-      {"a%0+ d", {Conv::d}, "[a]{0+ d:1$d}"},
-      {"a% +0d", {Conv::d}, "[a]{ +0d:1$d}"},
-      {"a%0 +d", {Conv::d}, "[a]{0 +d:1$d}"},
-      {"a% 0+d", {Conv::d}, "[a]{ 0+d:1$d}"},
-      {"a%+   0+d", {Conv::d}, "[a]{+   0+d:1$d}"},
+      {"a%+ 0d", {FormatConversionCharSetInternal::d}, "[a]{+ 0d:1$d}"},
+      {"a%+0 d", {FormatConversionCharSetInternal::d}, "[a]{+0 d:1$d}"},
+      {"a%0+ d", {FormatConversionCharSetInternal::d}, "[a]{0+ d:1$d}"},
+      {"a% +0d", {FormatConversionCharSetInternal::d}, "[a]{ +0d:1$d}"},
+      {"a%0 +d", {FormatConversionCharSetInternal::d}, "[a]{0 +d:1$d}"},
+      {"a% 0+d", {FormatConversionCharSetInternal::d}, "[a]{ 0+d:1$d}"},
+      {"a%+   0+d", {FormatConversionCharSetInternal::d}, "[a]{+   0+d:1$d}"},
   };
   for (const auto& e : kExpect) {
     SCOPED_TRACE(e.in);