[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

clang/include/clang/Driver/Options.td

@@ -6099,6 +6099,10 @@ def _SLASH_o : CLJoinedOrSeparate<"o">,
   HelpText<"Deprecated (set output file name); use /Fe or /Fe">,
   MetaVarName<"<file or dir/>">;
 def _SLASH_P : CLFlag<"P">, HelpText<"Preprocess to file">;
+def _SLASH_permissive : CLFlag<"permissive">,
+  HelpText<"Enable some non conforming code to compile">;
+def _SLASH_permissive_ : CLFlag<"permissive-">,
+  HelpText<"Disable non conforming code from compiling (default)">;
 def _SLASH_Tc : CLCompileJoinedOrSeparate<"Tc">,
   HelpText<"Treat <file> as C source file">, MetaVarName<"<file>">;
 def _SLASH_TC : CLCompileFlag<"TC">, HelpText<"Treat all source files as C">;
@@ -6180,7 +6184,6 @@ def _SLASH_FS : CLIgnoredFlag<"FS">;
 def _SLASH_JMC : CLIgnoredFlag<"JMC">;
 def _SLASH_kernel_ : CLIgnoredFlag<"kernel-">;
 def _SLASH_nologo : CLIgnoredFlag<"nologo">;
-def _SLASH_permissive_ : CLIgnoredFlag<"permissive-">;
 def _SLASH_RTC : CLIgnoredJoined<"RTC">;
 def _SLASH_sdl : CLIgnoredFlag<"sdl">;
 def _SLASH_sdl_ : CLIgnoredFlag<"sdl-">;

clang/lib/Driver/ToolChains/MSVC.cpp

@@ -1523,6 +1523,20 @@ static void TranslateDArg(Arg *A, llvm::opt::DerivedArgList &DAL,
   DAL.AddJoinedArg(A, Opts.getOption(options::OPT_D), NewVal);
 }
 
+static void TranslatePermissive(Arg *A, llvm::opt::DerivedArgList &DAL,
+                                const OptTable &Opts) {
+  DAL.AddFlagArg(A, Opts.getOption(options::OPT__SLASH_Zc_twoPhase_));
+  DAL.AddFlagArg(A, Opts.getOption(options::OPT_fno_operator_names));
+  // There is currently no /Zc:strictStrings- in clang-cl
+}
+
+static void TranslatePermissiveMinus(Arg *A, llvm::opt::DerivedArgList &DAL,
+                                     const OptTable &Opts) {
+  DAL.AddFlagArg(A, Opts.getOption(options::OPT__SLASH_Zc_twoPhase));
+  DAL.AddFlagArg(A, Opts.getOption(options::OPT_foperator_names));
+  DAL.AddFlagArg(A, Opts.getOption(options::OPT__SLASH_Zc_strictStrings));
+}
+
 llvm::opt::DerivedArgList *
 MSVCToolChain::TranslateArgs(const llvm::opt::DerivedArgList &Args,
                              StringRef BoundArch,
@@ -1565,6 +1579,12 @@ MSVCToolChain::TranslateArgs(const llvm::opt::DerivedArgList &Args,
     } else if (A->getOption().matches(options::OPT_D)) {
       // Translate -Dfoo#bar into -Dfoo=bar.
       TranslateDArg(A, *DAL, Opts);
+    } else if (A->getOption().matches(options::OPT__SLASH_permissive)) {
+      // Expand /permissive
+      TranslatePermissive(A, *DAL, Opts);
+    } else if (A->getOption().matches(options::OPT__SLASH_permissive_)) {
+      // Expand /permissive-
+      TranslatePermissiveMinus(A, *DAL, Opts);
     } else if (OFK != Action::OFK_HIP) {
       // HIP Toolchain translates input args by itself.
       DAL->append(A);

clang/test/Driver/cl-permissive.c

@@ -0,0 +1,17 @@
+// Note: %s must be preceded by --, otherwise it may be interpreted as a
+// command-line option, e.g. on Mac where %s is commonly under /Users.
+
+// RUN: %clang_cl /permissive -### -- %s 2>&1 | FileCheck -check-prefix=PERMISSIVE %s
+// PERMISSIVE: "-fno-operator-names"
+// PERMISSIVE: "-fdelayed-template-parsing"
+// RUN: %clang_cl /permissive- -### -- %s 2>&1 | FileCheck -check-prefix=PERMISSIVE-MINUS %s
+// PERMISSIVE-MINUS-NOT: "-fno-operator-names"
+// PERMISSIVE-MINUS-NOT: "-fdelayed-template-parsing"
+
+// The switches set by permissive may then still be manually enabled or disabled
+// RUN: %clang_cl /permissive /Zc:twoPhase -### -- %s 2>&1 | FileCheck -check-prefix=PERMISSIVE-OVERWRITE %s
+// PERMISSIVE-OVERWRITE: "-fno-operator-names"
+// PERMISSIVE-OVERWRITE-NOT: "-fdelayed-template-parsing"
+// RUN: %clang_cl /permissive- /Zc:twoPhase- -### -- %s 2>&1 | FileCheck -check-prefix=PERMISSIVE-MINUS-OVERWRITE %s
+// PERMISSIVE-MINUS-OVERWRITE-NOT: "-fno-operator-names"
+// PERMISSIVE-MINUS-OVERWRITE: "-fdelayed-template-parsing"