[C++2b] Implement multidimentional subscript operator

Implement P2128R6 in C++23 mode.

Unlike GCC's implementation, this doesn't try to recover when a user
meant to use a comma expression.

Because the syntax changes meaning in C++23, the patch is *NOT*
implemented as an extension. Instead, declaring an array with not
exactly 1 parameter is an error in older languages modes. There is an
off-by-default extension warning in C++23 mode.

Unlike the standard, we supports default arguments;

Ie, we assume, based on conversations in WG21, that the proposed
resolution to CWG2507 will be accepted.

We allow arrays OpenMP sections and C++23 multidimensional array to
coexist:

[a , b] multi dimensional array
[a : b] open mp section
[a, b: c] // error

The rest of the patch is relatively straight forward: we take care to
support an arbitrary number of arguments everywhere.

1 files changed, 2 insertions, 2 deletions

diff --git a/clang-tools-extra/clang-tidy/modernize/LoopConvertUtils.cpp b/clang-tools-extra/clang-tidy/modernize/LoopConvertUtils.cpp
index d29e631..5d4f3b8 100644
--- a/clang-tools-extra/clang-tidy/modernize/LoopConvertUtils.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/LoopConvertUtils.cpp
@@ -398,8 +398,8 @@ static bool isAliasDecl(ASTContext *Context, const Decl *TheDecl,
     if (OpCall->getOperator() == OO_Star)
       return isDereferenceOfOpCall(OpCall, IndexVar);
     if (OpCall->getOperator() == OO_Subscript) {
-      assert(OpCall->getNumArgs() == 2);
-      return isIndexInSubscriptExpr(OpCall->getArg(1), IndexVar);
+      return OpCall->getNumArgs() == 2 &&
+             isIndexInSubscriptExpr(OpCall->getArg(1), IndexVar);
     }
     break;
   }