clang-cl: Ignore /Zc:externConstexpr and /Zc:throwingNew

[ki.stfu]

Summary

The first option tells the compiler to use external linkage for constexpr variables, and the second one prevents null checks after operator new which can throw.

See https://docs.microsoft.com/en-us/cpp/build/reference/zc-externconstexpr and https://docs.microsoft.com/en-us/cpp/build/reference/zc-throwingnew-assume-operator-new-throws

[ki.stfu]

Not sure, but I'd be surprised if Clang behaves like MSVC in one of these cases.

[ki.stfu]

@rsmith Friendly ping.

[hans]

I'm not sure ignoring these is the right thing to do. Maybe they should be "Unsupported but parsed options" instead?

[ki.stfu]

@hans they are ignored because Clang behaves like MSVC with these options
enabled (C++ standard conformance mode)

[hans]

In D87372#2376305, @ki.stfu wrote:

@hans they are ignored because Clang behaves like MSVC with these options
enabled (C++ standard conformance mode)

Ah, I got it backwards. Yeah, ignoring these makes sense.

Can you add the variants with trailing dash (e.g. /Zc:externConstexpr-) as parsed but unsupported?

clang/include/clang/Driver/Options.td

 def _SLASH_RTC : CLIgnoredJoined<"RTC">;
 def _SLASH_sdl : CLIgnoredFlag<"sdl">;
 def _SLASH_sdl_ : CLIgnoredFlag<"sdl-">;
 def _SLASH_utf8 : CLIgnoredFlag<"utf-8">,
   HelpText<"Set source and runtime encoding to UTF-8 (default)">;
 def _SLASH_w : CLIgnoredJoined<"w">;
 def _SLASH_Zc___cplusplus : CLIgnoredFlag<"Zc:__cplusplus">;
 def _SLASH_Zc_auto : CLIgnoredFlag<"Zc:auto">;
+def _SLASH_Zc_externConstexpr : CLIgnoredFlag<"Zc:externConstexpr">;
 def _SLASH_Zc_forScope : CLIgnoredFlag<"Zc:forScope">;
 def _SLASH_Zc_inline : CLIgnoredFlag<"Zc:inline">;
 def _SLASH_Zc_rvalueCast : CLIgnoredFlag<"Zc:rvalueCast">;
 def _SLASH_Zc_ternary : CLIgnoredFlag<"Zc:ternary">;
+def _SLASH_Zc_throwingNew : CLIgnoredFlag<"Zc:throwingNew">;
 def _SLASH_Zc_wchar_t : CLIgnoredFlag<"Zc:wchar_t">;
 def _SLASH_ZH_MD5 : CLIgnoredFlag<"ZH:MD5">;
 def _SLASH_ZH_SHA1 : CLIgnoredFlag<"ZH:SHA1">;
 def _SLASH_ZH_SHA_256 : CLIgnoredFlag<"ZH:SHA_256">;
 def _SLASH_Zm : CLIgnoredJoined<"Zm">;
 def _SLASH_Zo : CLIgnoredFlag<"Zo">;
 def _SLASH_Zo_ : CLIgnoredFlag<"Zo-">;
 

clang/test/Driver/cl-options.c

 // RUN:    /source-charset:utf-8 \
 // RUN:    /utf-8 \
 // RUN:    /vmg \
 // RUN:    /volatile:iso \
 // RUN:    /w12345 \
 // RUN:    /wd1234 \
 // RUN:    /Zc:__cplusplus \
 // RUN:    /Zc:auto \
+// RUN:    /Zc:externConstexpr \
 // RUN:    /Zc:forScope \
 // RUN:    /Zc:inline \
 // RUN:    /Zc:rvalueCast \
 // RUN:    /Zc:ternary \
+// RUN:    /Zc:throwingNew \
 // RUN:    /Zc:wchar_t \
 // RUN:    /ZH:MD5 \
 // RUN:    /ZH:SHA1 \
 // RUN:    /ZH:SHA_256 \
 // RUN:    /Zm \
 // RUN:    /Zo \
 // RUN:    /Zo- \
 // RUN:    -### -- %s 2>&1 | FileCheck -check-prefix=IGNORED %s