rejects-valid if parenthesized temporary is followed by array indexing

[zygoloid]

Bugzilla Link	20349
Version	unspecified
OS	Linux
CC	@DougGregor

Extended Description

Clang rejects this valid code in C++11 onwards:

  struct S { S operator[](int); S operator()(); };
  int n;
  void f() { (S())[n](); }

The problem is that we commit to handling the [ as the start of a lambda-expression too early.

We also incorrectly reject the above testcase in Objective-C++ mode, because we think the [ is the start of a message send expression.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[Endilll]

Issue in C++11 mode is still there. Since Clang 6 this example is rejected in Objective-C++ mode for the same reason as in C++11 mode.
https://godbolt.org/z/hh6re75Wf

[shafik]

CC @rjmccall

[rjmccall]

This is weird because neither a lambda nor a message send is even legal in this position. Are we falling into a recovery path for some reason?

[cor3ntin]

EWG approved the resolution of CWG2228 as described here https://cplusplus.github.io/CWG/issues/2228.html, which would fix this issue