[REVISED PATCH 2/9]: C++ P0482R5 char8_t: Core language support

Tom Honermann tom@honermann.net
Mon Dec 24 02:27:00 GMT 2018

Attached is a revised patch that addresses changes in P0482R6 as well as 
feedback provided by Jason.  Changes from the prior patch include:
- Updated the value of the __cpp_char8_t feature test macro to 201811
   per P0482R6.
- Enable char8_t support with -std=c++2a per adoption of P0482R6 in
   San Diego.
- Reverted the unnecessary changes to gcc/gcc/c/c-typeck.c as requested
   by Jason.
- Removed unnecessary checks of 'flag_char8_t' within the C++ front
   end as requested by Jason.
- Corrected the regression spotted by Jason regarding initialization of
   signed char and unsigned char arrays with string literals.
- Made minor changes to the error message emitted for ill-formed
   initialization of char arrays with UTF-8 string literals.  These
   changes do not yet implement Jason's suggestion; I'll follow up with a
   separate patch for that due to additional test impact.

Tested on x86_64-linux.


2018-11-04  Tom Honermann  <tom@honermann.net>

      * defaults.h: Define CHAR8_TYPE.


2018-11-04  Tom Honermann  <tom@honermann.net>
      * c-family/c-common.c (c_common_reswords): Add char8_t.
      (fix_string_type): Use char8_t for the type of u8 string literals.
      (c_common_get_alias_set): char8_t doesn't alias.
      (c_common_nodes_and_builtins): Define char8_t as a builtin type in
      (c_stddef_cpp_builtins): Add __CHAR8_TYPE__.
      (keyword_begins_type_specifier): Add RID_CHAR8.
      * c-family/c-common.h (rid): Add RID_CHAR8.
      (c_tree_index): Add CTI_CHAR8_TYPE and CTI_CHAR8_ARRAY_TYPE.
      Define D_CXX_CHAR8_T and D_CXX_CHAR8_T_FLAGS.
      Define char8_type_node and char8_array_type_node.
      * c-family/c-cppbuiltin.c (cpp_atomic_builtins): Predefine
      (c_cpp_builtins): Predefine __cpp_char8_t.
      * c-family/c-lex.c (lex_string): Use char8_array_type_node as the
      type of CPP_UTF8STRING.
      (lex_charconst): Use char8_type_node as the type of CPP_UTF8CHAR.
      * c-family/c-opts.c: If not otherwise specified, enable -fchar8_t
      when targeting C++2a.
      * c-family/c.opt: Add the -fchar8_t command line option.


2018-11-04  Tom Honermann  <tom@honermann.net>

      * cp/cvt.c (type_promotes_to): Handle char8_t promotion.
      * cp/decl.c (grokdeclarator): Handle invalid type specifier
      combinations involving char8_t.
      * cp/lex.c (init_reswords): Add char8_t as a reserved word.
      * cp/mangle.c (write_builtin_type): Add name mangling for char8_t
      * cp/parser.c (cp_keyword_starts_decl_specifier_p,
      cp_parser_simple_type_specifier): Recognize char8_t as a simple
      type specifier.
      (cp_parser_string_literal): Use char8_array_type_node for the type
      of CPP_UTF8STRING.
      (cp_parser_set_decl_spec_type): Tolerate char8_t typedefs in system
      * cp/rtti.c (emit_support_tinfos): type_info support for char8_t.
      * cp/tree.c (char_type_p): Recognize char8_t as a character type.
      * cp/typeck.c (string_conv_p): Handle conversions of u8 string
      literals of char8_t type.
      (check_literal_operator_args): Handle UDLs with u8 string literals
      of char8_t type.
      * cp/typeck2.c (digest_init_r): Disallow initializing a char array
      with a u8 string literal.


2018-10-31  Tom Honermann  <tom@honermann.net>
      * cp-demangle.c (cplus_demangle_builtin_types,
      cplus_demangle_type): Add name demangling for char8_t (Du).
      * cp-demangle.h: Increase D_BUILTIN_TYPE_COUNT to accommodate the
      new char8_t type.


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