[NFC][libc++][format] Generalizes bracket parsing.

Both the tuple formatter and range formatter parse a bracket. Instead of
implementing this twice do it in the generic parser. This is preparation
to improve the diagnostics in the format library.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D155264

3 files changed, 50 insertions, 45 deletions

diff --git a/libcxx/include/__format/formatter_tuple.h b/libcxx/include/__format/formatter_tuple.h
index 18d41d3..e06f945 100644
--- a/libcxx/include/__format/formatter_tuple.h
+++ b/libcxx/include/__format/formatter_tuple.h
@@ -51,18 +51,16 @@ struct _LIBCPP_TEMPLATE_VIS __formatter_tuple {
     auto __begin = __parser_.__parse(__ctx, __format_spec::__fields_tuple);
 
     auto __end = __ctx.end();
-    if (__begin != __end) {
-      if (*__begin == _CharT('m')) {
-        if constexpr (sizeof...(_Args) == 2) {
-          set_separator(_LIBCPP_STATICALLY_WIDEN(_CharT, ": "));
-          set_brackets({}, {});
-          ++__begin;
-        } else
-          std::__throw_format_error("The format specifier m requires a pair or a two-element tuple");
-      } else if (*__begin == _CharT('n')) {
+    // Note 'n' is part of the type here
+    if (__parser_.__clear_brackets_)
+      set_brackets({}, {});
+    else if (__begin != __end && *__begin == _CharT('m')) {
+      if constexpr (sizeof...(_Args) == 2) {
+        set_separator(_LIBCPP_STATICALLY_WIDEN(_CharT, ": "));
         set_brackets({}, {});
         ++__begin;
-      }
+      } else
+        std::__throw_format_error("The format specifier m requires a pair or a two-element tuple");
     }
 
     if (__begin != __end && *__begin != _CharT('}'))
diff --git a/libcxx/include/__format/parser_std_format_spec.h b/libcxx/include/__format/parser_std_format_spec.h
index 2f7ccdf..6f60ba8 100644
--- a/libcxx/include/__format/parser_std_format_spec.h
+++ b/libcxx/include/__format/parser_std_format_spec.h
@@ -119,42 +119,47 @@ __substitute_arg_id(basic_format_arg<_Context> __format_arg) {
 /// explicitly.
 // TODO FMT Use an ABI tag for this struct.
 struct __fields {
-  uint8_t __sign_ : 1 {false};
-  uint8_t __alternate_form_ : 1 {false};
-  uint8_t __zero_padding_ : 1 {false};
-  uint8_t __precision_ : 1 {false};
-  uint8_t __locale_specific_form_ : 1 {false};
-  uint8_t __type_ : 1 {false};
+  uint16_t __sign_                 : 1 {false};
+  uint16_t __alternate_form_       : 1 {false};
+  uint16_t __zero_padding_         : 1 {false};
+  uint16_t __precision_            : 1 {false};
+  uint16_t __locale_specific_form_ : 1 {false};
+  uint16_t __type_                 : 1 {false};
   // Determines the valid values for fill.
   //
   // Originally the fill could be any character except { and }. Range-based
   // formatters use the colon to mark the beginning of the
   // underlying-format-spec. To avoid parsing ambiguities these formatter
   // specializations prohibit the use of the colon as a fill character.
-  uint8_t __use_range_fill_ : 1 {false};
+  uint16_t __use_range_fill_ : 1 {false};
+  uint16_t __clear_brackets_ : 1 {false};
+  uint16_t __consume_all_    : 1 {false};
 };
 
 // By not placing this constant in the formatter class it's not duplicated for
 // char and wchar_t.
+inline constexpr __fields __fields_bool{.__locale_specific_form_ = true, .__type_ = true, .__consume_all_ = true};
 inline constexpr __fields __fields_integral{
     .__sign_                 = true,
     .__alternate_form_       = true,
     .__zero_padding_         = true,
     .__locale_specific_form_ = true,
-    .__type_                 = true};
+    .__type_                 = true,
+    .__consume_all_          = true};
 inline constexpr __fields __fields_floating_point{
     .__sign_                 = true,
     .__alternate_form_       = true,
     .__zero_padding_         = true,
     .__precision_            = true,
     .__locale_specific_form_ = true,
-    .__type_                 = true};
-inline constexpr __fields __fields_string{.__precision_ = true, .__type_ = true};
-inline constexpr __fields __fields_pointer{.__zero_padding_ = true, .__type_ = true};
+    .__type_                 = true,
+    .__consume_all_          = true};
+inline constexpr __fields __fields_string{.__precision_ = true, .__type_ = true, .__consume_all_ = true};
+inline constexpr __fields __fields_pointer{.__zero_padding_ = true, .__type_ = true, .__consume_all_ = true};
 
 #  if _LIBCPP_STD_VER >= 23
-inline constexpr __fields __fields_tuple{.__use_range_fill_ = true};
-inline constexpr __fields __fields_range{.__use_range_fill_ = true};
+inline constexpr __fields __fields_tuple{.__use_range_fill_ = true, .__clear_brackets_ = true};
+inline constexpr __fields __fields_range{.__use_range_fill_ = true, .__clear_brackets_ = true};
 inline constexpr __fields __fields_fill_align_width{};
 #  endif
 
@@ -330,15 +335,17 @@ public:
     if (__fields.__locale_specific_form_ && __parse_locale_specific_form(__begin) && __begin == __end)
       return __begin;
 
-    if (__fields.__type_) {
+    if (__fields.__clear_brackets_ && __parse_clear_brackets(__begin) && __begin == __end)
+      return __begin;
+
+    if (__fields.__type_)
       __parse_type(__begin);
 
-      // When __type_ is false the calling parser is expected to do additional
-      // parsing. In that case that parser should do the end of format string
-      // validation.
-      if (__begin != __end && *__begin != _CharT('}'))
-        std::__throw_format_error("The format-spec should consume the input or end with a '}'");
-    }
+    if (!__fields.__consume_all_)
+      return __begin;
+
+    if (__begin != __end && *__begin != _CharT('}'))
+      std::__throw_format_error("The format-spec should consume the input or end with a '}'");
 
     return __begin;
   }
@@ -377,7 +384,7 @@ public:
   __sign __sign_ : 2 {__sign::__default};
   bool __alternate_form_ : 1 {false};
   bool __locale_specific_form_ : 1 {false};
-  bool __reserved_0_ : 1 {false};
+  bool __clear_brackets_       : 1 {false};
   __type __type_{__type::__default};
 
   // These flags are only used for formatting chrono. Since the struct has
@@ -392,8 +399,8 @@ public:
 
   bool __month_name_ : 1 {false};
 
-  uint8_t __reserved_1_ : 2 {0};
-  uint8_t __reserved_2_ : 6 {0};
+  uint8_t __reserved_0_ : 2 {0};
+  uint8_t __reserved_1_ : 6 {0};
   // These two flags are only used internally and not part of the
   // __parsed_specifications. Therefore put them at the end.
   bool __width_as_arg_ : 1 {false};
@@ -625,6 +632,16 @@ private:
   }
 
   template <contiguous_iterator _Iterator>
+  _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_clear_brackets(_Iterator& __begin) {
+    if (*__begin != _CharT('n'))
+      return false;
+
+    __clear_brackets_ = true;
+    ++__begin;
+    return true;
+  }
+
+  template <contiguous_iterator _Iterator>
   _LIBCPP_HIDE_FROM_ABI constexpr void __parse_type(_Iterator& __begin) {
     // Determines the type. It does not validate whether the selected type is
     // valid. Most formatters have optional fields that are only allowed for
diff --git a/libcxx/include/__format/range_formatter.h b/libcxx/include/__format/range_formatter.h
index ca3ee9a..30d3a98 100644
--- a/libcxx/include/__format/range_formatter.h
+++ b/libcxx/include/__format/range_formatter.h
@@ -64,18 +64,8 @@ struct _LIBCPP_TEMPLATE_VIS range_formatter {
 
     // The n field overrides a possible m type, therefore delay applying the
     // effect of n until the type has been procesed.
-    bool __clear_brackets = (*__begin == _CharT('n'));
-    if (__clear_brackets) {
-      ++__begin;
-      if (__begin == __end) [[unlikely]] {
-        // Since there is no more data, clear the brackets before returning.
-        set_brackets({}, {});
-        return __parse_empty_range_underlying_spec(__ctx, __begin);
-      }
-    }
-
     __parse_type(__begin, __end);
-    if (__clear_brackets)
+    if (__parser_.__clear_brackets_)
       set_brackets({}, {});
     if (__begin == __end) [[unlikely]]
       return __parse_empty_range_underlying_spec(__ctx, __begin);
@@ -110,7 +100,7 @@ struct _LIBCPP_TEMPLATE_VIS range_formatter {
       // [format.range.formatter]/6
       //   If the range-type is s or ?s, then there shall be no n option and no
       //   range-underlying-spec.
-      if (__clear_brackets) {
+      if (__parser_.__clear_brackets_) {
         if (__parser_.__type_ == __format_spec::__type::__string)
           std::__throw_format_error("The n option and type s can't be used together");
         std::__throw_format_error("The n option and type ?s can't be used together");