C23 feature support checklist

[Vexu]

Based on https://en.cppreference.com/w/c/23

• _Static_asert with no message
• [[nodiscard]]
• [[maybe_unused]]
• [[deprecated]]
• Attributes
  - [ ] IEEE 754 decimal floating-point types
  • Add IEEE 754 interchange and extended types #552
• [[fallthrough]]
• u8 character constants
• Removal of function definitions without prototype
• [[nodiscard]] with message
• Unnamed parameters in function definitions
• Labels before declarations and end of blocks
• Binary integer constants
• __has_c_attribute in preprocessor conditionals
• __has_c_attribute(vendor::attribute)
• Allow duplicate attributes
  - [ ] IEEE 754 interchange and extended types
  • Add IEEE 754 interchange and extended types #552
• Digit separators
• #elifdef and #elifndef
• Type change of u8 string literals
• [[maybe_unused]] for labels
• #warning
• Bit-precise integer types (_BitInt)
• [[noreturn]]
• Suffixes for bit-precise integer constants
• __has_include in preprocessor conditionals
• Removal of function declarations without prototype
• Empty initializers
• typeof ...
• ... and typeof_unqual
• New spelling of keywords
• Predefined true and false
• [[unsequenced]]
• [[reproducible]]
• Relax requirements for variadic parameter list
• Type inference in object definitions (auto)
• constexpr objects
• nullptr
• #embed
• #embed parameters limit, suffix, prefix, if_empty
• __has_embed
• Storage-class specifiers for compound literals
• __VA_OPT__
• Identifier Syntax using Unicode Standard Annex 31
• Check identifier NFC normalized
• Type change of u8 string literals
• u8 character constants (already implemented, should be an error for older versions)

[ehaas]

This list may also be helpful for test cases: https://htmlpreview.github.io/?https://icube-forge.unistra.fr/icps/c23-library/-/raw/main/README.html

[Vexu]

@ehaas Do you want to handle the Unicode identifier change?

[ehaas]

Sure. The list of acceptable start/continuation characters should be straightforward. I've never done anything with unicode normalization so I don't know how much work that will be, but I think it will fit nicely with the string interner and there won't be too much incidental complexity around adding it.