clang-cl: Support the /Zc:twoPhase[-] command-line option (PR32680)

[hans]

Summary

It sounds like MSVC is adding support for two-phase name lookup in a future version, enabled by this flag (see bug).

[hans]

We could wait until a version of MSVC ships with this, in case they decide to change the name, or we could just land it now.

[rnk]

Let's add it now. If we don't add this, some user will run into it first and have to wait for a fix. If we add it and get the meaning wrong, we'll still need to fix it and push a new release, so we're no worse off.

lgtm

include/clang/Driver/CLCompatOptions.td

def _SLASH_Zc_threadSafeInit : CLFlag<"Zc:threadSafeInit">,
   Alias<fthreadsafe_statics>;
 def _SLASH_Zc_threadSafeInit_ : CLFlag<"Zc:threadSafeInit-">,
   HelpText<"Disable thread-safe initialization of static variables">,
   Alias<fno_threadsafe_statics>;
 def _SLASH_Zc_trigraphs : CLFlag<"Zc:trigraphs">,
   HelpText<"Enable trigraphs">, Alias<ftrigraphs>;
 def _SLASH_Zc_trigraphs_off : CLFlag<"Zc:trigraphs-">,
   HelpText<"Disable trigraphs (default)">, Alias<fno_trigraphs>;
+def _SLASH_Zc_twoPhase : CLFlag<"Zc:twoPhase">,
+  HelpText<"Enable two-phase name lookup in templates">,
+  Alias<fno_delayed_template_parsing>;
+def _SLASH_Zc_twoPhase_ : CLFlag<"Zc:twoPhase-">,
+  HelpText<"Disable two-phase name lookup in templates">,
+  Alias<fdelayed_template_parsing>;
 def _SLASH_Z7 : CLFlag<"Z7">,
   HelpText<"Enable CodeView debug information in object files">;
 def _SLASH_Zd : CLFlag<"Zd">,
   HelpText<"Emit debug line number tables only">;
 def _SLASH_Zi : CLFlag<"Zi">, Alias<_SLASH_Z7>,
   HelpText<"Alias for /Z7. Does not produce PDBs.">;
 def _SLASH_Zp : CLJoined<"Zp">,
   HelpText<"Specify the default maximum struct packing alignment">,

test/Driver/cl-options.c

 // RUN: %clang_cl -c -### -- %s 2>&1 | FileCheck -check-prefix=DEFAULTSTRICT %s
 // DEFAULTSTRICT: "-relaxed-aliasing"
 // RUN: %clang_cl -c -fstrict-aliasing -### -- %s 2>&1 | FileCheck -check-prefix=STRICT %s
 // STRICT-NOT: "-relaxed-aliasing"
 // RUN: %clang_cl -c -fno-strict-aliasing -### -- %s 2>&1 | FileCheck -check-prefix=NOSTRICT %s
 // NOSTRICT: "-relaxed-aliasing"
 
 // We recognize -f[no-]delayed-template-parsing.
+// /Zc:twoPhase[-] has the opposite meaning.
 // RUN: %clang_cl -c -### -- %s 2>&1 | FileCheck -check-prefix=DELAYEDDEFAULT %s
 // DELAYEDDEFAULT: "-fdelayed-template-parsing"
 // RUN: %clang_cl -c -fdelayed-template-parsing -### -- %s 2>&1 | FileCheck -check-prefix=DELAYEDON %s
+// RUN: %clang_cl -c /Zc:twoPhase- -### -- %s 2>&1 | FileCheck -check-prefix=DELAYEDON %s
 // DELAYEDON: "-fdelayed-template-parsing"
 // RUN: %clang_cl -c -fno-delayed-template-parsing -### -- %s 2>&1 | FileCheck -check-prefix=DELAYEDOFF %s
+// RUN: %clang_cl -c /Zc:twoPhase -### -- %s 2>&1 | FileCheck -check-prefix=DELAYEDOFF %s
 // DELAYEDOFF-NOT: "-fdelayed-template-parsing"
 
 // For some warning ids, we can map from MSVC warning to Clang warning.
 // RUN: %clang_cl -wd4005 -wd4100 -wd4910 -wd4996 -### -- %s 2>&1 | FileCheck -check-prefix=Wno %s
 // Wno: "-cc1"
 // Wno: "-Wno-macro-redefined"
 // Wno: "-Wno-unused-parameter"
 // Wno: "-Wno-dllexport-explicit-instantiation-decl"