[clang] [Clang][C++26] Implement Pack Indexing (P2662R3). (PR #72644)

[Nikolas Klauser via cfe-commits]

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@@ -978,6 +978,20 @@ bool Parser::ConsumeAndStoreFunctionPrologue(CachedTokens &Toks) {
       } else {
         break;
       }
+      // Pack indexing
+      if (getLangOpts().CPlusPlus26 && Tok.is(tok::ellipsis) &&
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philnik777 wrote:

> @philnik777 This would require GCC to also support that as an extension in C++11 (and above). Otherwise we wouldn't be able to use it in our tuple implementation.

Yeah, obviously. But if one implementation adds it, it becomes a lot more likely that others do it too. I also suspect that libstdc++ may also really like this.



> Would a change like that be possible without being an ABI break?

I don't know, but IMO it would even be worth just adding it in ABIv2 if we can get it as an extension. I expect this to bring a _lot_ of improvement in terms of compile times and debug binary size.

https://github.com/llvm/llvm-project/pull/72644