https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100493
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:1420ff3efcff98df0e8c6f021a7ff24b5fc65043 commit r12-5578-g1420ff3efcff98df0e8c6f021a7ff24b5fc65043 Author: Patrick Palka <ppa...@redhat.com> Date: Mon Nov 29 07:52:47 2021 -0500 c++: redundant explicit 'this' capture before C++20 [PR100493] As described in detail in the PR, in C++20 implicitly capturing 'this' via a '=' capture default is deprecated, and in C++17 adding an explicit 'this' capture alongside a '=' capture default is diagnosed as redundant (and is strictly speaking ill-formed). This means it's impossible to write, in a forward-compatible way, a C++17 lambda that has a '=' capture default and that also captures 'this' (implicitly or explicitly): [=] { this; } // #1 deprecated in C++20, OK in C++17 // GCC issues a -Wdeprecated warning in C++20 mode [=, this] { } // #2 ill-formed in C++17, OK in C++20 // GCC issues an unconditional warning in C++17 mode This patch resolves this dilemma by downgrading the warning for #2 into a -pedantic one. In passing, move it into the -Wc++20-extensions class of warnings and adjust its wording accordingly. PR c++/100493 gcc/cp/ChangeLog: * parser.c (cp_parser_lambda_introducer): In C++17, don't diagnose a redundant 'this' capture alongside a by-copy capture default unless -pedantic. Move the diagnostic into -Wc++20-extensions and adjust wording accordingly. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/lambda-this1.C: Adjust expected diagnostics. * g++.dg/cpp1z/lambda-this8.C: New test. * g++.dg/cpp2a/lambda-this3.C: Compile with -pedantic in C++17 to continue to diagnose redundant 'this' captures.
