@ldionne Thanks! Could you commit it for me (hyd-dev <yd-huang@outlook.com>)?

Update the test to use #if defineds and #error.

Add a test (libcxx/test/libcxx/libcpp_freestanding.sh.cpp).

I don't have commit access. @njames93 Could you please commit it for me (hyd-dev <yd-huang@outlook.com>)? Thanks!

Ping?

Address the comment: remove PathSize from BuiltinBitCastExpr's constructor and assert() it == 0.

If this is OK, please commit it with --author "hyd-dev <yd-huang@outlook.com>". Thanks.

Ping?

Ping?

Fix typos in the summary.

Format builtin-bit-cast.cpp and make it simpler.

Any reply?

In D79477#2028637, @njames93 wrote:

What I mean to say is, if the behaviour of the testing environment changes to pipe the result to a terminal that supports color, it could cause this test case to also fail.

The standard output is always piped to FileCheck's standard input. It will never become "a terminal that supports color".
Standard error is not redirected explicitly, but it is not used to detect color support.

Would a test case be needed?

clang::tidy::clangTidyMain() shows that clang-tidy reports all diagnostics by clang::tidy::handleErrors(), which constructs a clang::tidy::(anonymous namespace)::ErrorReporter, no matter where they come from, so I think a test case is not required.

Not a fan of this test case as it only demonstrates the color behaviour of the process running the check not the actual option itself

What does "option itself" mean?

Fair point, will this option also control the color of the diagnostics emitted by clang or just clang tidy specific diagnostics?

This option sets DiagOpts->ShowColors to true. As I known, it controls all diagnostics reported by the clang-tidy program (by clang::tidy::(anonymous namespace)::ErrorReporter), including clang-diagnostic-* and other clang-tidy checks.

None of the clang-tidy command line options are prefixed with -f.
This command line option used to be --color-diagnostics, but I've followed @hokein's advice to change it to --use-color.
If you mean to use the -fcolor-diagnostics option from compile_commands.json, clang-tidy and clang are two separate tools. The users may not want them to share the same setting, because they may invoke them in different environments.

Change incorrect detect to detected in the comment of UseColor option.

Say the --use-color command line option overrides the UseColor option in .clang-tidy file in its help text.

Rename clang-tools-extra/test/clang-tidy/infrastructure/color-diagnostics.cpp to use-color.cpp.

Address the comments above.
I also removed the incorrect DefaultOptions.ColorDiagnostics = ColorDiagnostics in ClangTidyMain.cpp. That produces incorrect UseColor: false with -dump-config.