[Dwarf-discuss] Proposal: Define a language version scheme for Swift

[Adrian Prantl]

# Swift Language version scheme

## Background

The list of languages at https://dwarfstd.org/languages-v6.html does not list a version scheme for the Swift language. This proposal adds one.

## Overview

The Swift programming language does not have a version scheme defined for DW_AT_language_version. This proposal defines it to use the `VVMM` version scheme. This way "Swift 5.10" would be

```
DW_AT_language(DW_LANG_Swift)
DW_AT_language_version(510)
```

and "Swift 6" would be `DW_AT_language_version(600)`. Even though Swift package releases usually have a Major.Minor.Patch version scheme (e.g., Swift 5.9.2), the Swift compiler frontend's LangOptions data structure only uses Major.Minor to distinguish syntax changes in the parser (see References). This version scheme is designed to match what the compiler does.

## Proposed Changes

Augment the table of language encodings to say

```
Swift DW_LNAME_Swift 0x001a 0 VVMM
```

## Dependencies

Issue 210419.1 

## References

https://www.swift.org/download/ (see older releases for a history of versions).
https://github.com/apple/swift/blob/3d32f5fc8a9087add424a2704ef1dcd89c9307ff/include/swift/Basic/LangOptions.h#L174