[Dwarf-discuss] Proposal: C standard release dates for DW_AT_language_version, clarify semantics

[Jakub Jelinek]

On Wed, Apr 24, 2024 at 02:25:37PM -0700, Adrian Prantl via Dwarf-discuss wrote:
> # C standard release dates for DW_AT_language_version, clarify semantics
> 
> ## Background
> 
> The list of languages at https://dwarfstd.org/languages-v6.html does not list release dates for the ISO C standard. Producers need to know what version numbers they should produce though. I scanned the ISO website for appropriate dates to use.
> 
> ## Proposed Changes
> 
> Augment the table of language encodings to add
> C (K&R and ISO) DW_LNAME_C 0x0003 0 YYYYMM 
> 
> K&R 000000
> C89 198912
> C99 199912
> C11 201112
> C17 201806 (sic!)
> C2x >201806

That is not correct.
C99 199901
C11 201112
C17 201710
C23 202311

C89 with ammendment 1 would be
199409
C89 likely that 198912 indeed.

As for C++, the above page is missing
C++23 202302
> 
> Add the following non-normative wording: 
> 
> To convert a version number to a specific release, it is good practice to treat the YYYMM version numbers listed in this document as the maximum version that is interpreted as belonging to a specific release.

> This way consumers can emit version numbers for unreleased upcoming specifications, by using, e.g., the date the compiler was built.

That is not a good suggestion.
If a compiler supports some part of e.g. C23 but not everything, it should
be something larger than 201710 but smaller than 202311, even when the date
the compiler was built could be 202404 or later.
GCC and Clang up to 17 used e.g. 202000 for C23 partial implementations,
GCC still does, Clang 18+ now uses 202311.

	Jakub