[SwayamInSync]

Apple's <AssertMacros.h>, which some of Apple's framework headers include, defines check(assertion) as __Check(assertion) unless __ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORES is 0, and defaults it to 1. In production builds __Check expands to nothing. The macro is function-like and the preprocessor runs before the parser sees a construct, so every cppverify::check(...) after the header breaks. With Apple's latest published copy of the header (CarbonHeaders-18.1, apple-oss-distributions) and an arm64-apple-macosx14.0 target, main reports:

uses_check.cpp:8:19: error: expected unqualified-id
    8 |   cv::check(x > 0);
      |                   ^

The header's own comment names the fix: define the switch to 0, and it defines only its __Check, __Require, and __Verify names, which Apple recommends over the old ones.

The change: with -fverify-contracts on a Darwin target, InitializePreprocessor defines __ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORES to 0 before the implicit <cppverify.h>, unless the command line defines it. It comes after the command line's -D options, so -D__ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORES=1 keeps the old names. A #define of 1 in the source also takes effect, with a -Wmacro-redefined warning. Other targets and compilations without the flag are unaffected.

Docs: the syntax page gains a section on macros named like a construct. It has a checked example of a check macro breaking the construct, with its exact error and the #undef that restores it, and explains Apple's header and how a file that uses the old macro names keeps them. DESIGN records the predefinition. The release notes get an entry under "C++ that compiles now".

Testing: Verify/assert_macros_darwin.cpp, with a mock Inputs/apple/AssertMacros.h that keeps the header's logic, runs:

• on macOS and iOS triples, with -verify and no diagnostics;
• with the switch at 1 from the command line, which gives the old error;
• the final value of the switch, which is 0 with the flag on Apple, and 1 without the flag or on Linux.

On main exactly the three Apple-with-flag lines fail and the three control lines pass. With Apple's real header the function verifies through cpp-verify -- -target arm64-apple-macosx14.0 (main: the error above). I could not run it on macOS itself; the macOS CI job runs the Verify suite there.

Checked: the Verify and Preprocessor suites (813 tests) pass in a release build, except Preprocessor/llvm-windres.rc, which needs llvm-windres and that build does not have it. In a build with assertions they pass (800 passed, 13 unsupported). After the rebase onto #39, the documentation examples pass and the site builds with -W.