[all-commits] [llvm/llvm-project] c70b0e: [clang-cl] Add /permissive and /permissive-

[zero9178 via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c70b0e808da8e1650f3ee426698a8b87c94b8910
      https://github.com/llvm/llvm-project/commit/c70b0e808da8e1650f3ee426698a8b87c94b8910
  Author: Markus Böck <markus.boeck02 at gmail.com>
  Date:   2021-06-10 (Thu, 10 Jun 2021)

  Changed paths:
    M clang/include/clang/Driver/Options.td
    M clang/lib/Driver/ToolChains/MSVC.cpp
    A clang/test/Driver/cl-permissive.c

  Log Message:
  -----------
  [clang-cl] Add /permissive and /permissive-

This patch adds the command line options /permissive and /permissive- to clang-cl. These flags are used in MSVC to enable various /Zc language conformance options at once. In particular, /permissive is used to enable the various non standard behaviour of MSVC, while /permissive- is the opposite.

When either of two command lines are specified they are simply expanded to the various underlying /Zc options. In particular when /permissive is passed it currently expands to:

/Zc:twoPhase- (disable two phase lookup)
-fno-operator-names (disable C++ operator keywords)
/permissive- expands to the opposites of these flags + /Zc:strictStrings (/Zc:strictStrings- does not currently exist). In the future, if any more MSVC workarounds are ever added they can easily be added to the expansion. One is also able to override settings done by permissive. Specifying /permissive- /Zc:twoPhase- will apply the settings from permissive minus, but disables two phase lookup.

Motivation for this patch was mainly parity with MSVC as well as compatibility with Windows SDK headers. The /permissive page from MSVC documents various workarounds that have to be done for the Windows SDK headers [1], when MSVC is used with /permissive-. In these, Microsoft often recommends simply compiling with /permissive for the specified source files. Since some of these also apply to clang-cl (which acts like /permissive- by default mostly), and some are currently implemented as "hacks" within clang that I'd like to remove, adding /permissive and /permissive- to be in full parity with MSVC and Microsofts documentation made sense to me.

[1] https://docs.microsoft.com/en-us/cpp/build/reference/permissive-standards-conformance?view=msvc-160#windows-header-issues

Differential Revision: https://reviews.llvm.org/D103773