clang-cl: Make /Za disable oldnames.lib dependency

[hans]

Summary

This makes the /Za command-line flag disable inclusion of oldnames.lib as a dependency in object files. It's possible this flag should be doing more stuff, and therefore I haven't given it a HelpText, but this is a start.

[rnk]

LGTM

[cdavis5x]

This flag should be doing more stuff. This flag is supposed to request strict ANSI conformance (according to Microsoft's, uh... "unique" interpretation of that). That means at least (in GCC terms) -fno-ms-extensions, in addition to not auto-linking OLDNAMES.LIB. (The /Ze flag undoes the effects of /Za.)

I seem to recall someone from MS on cfe-dev (and yes, they do exist!) saying that /Za is broken and shouldn't be used (cf. "/Za considered harmful" or some such). Are you sure you want to implement it, given that?

[hans]

Closed by commit rL187991 (authored by @hans).

include/clang/Driver/CLCompatOptions.td

 def _SLASH_MT : CLFlag<"MT">, HelpText<"Use static run-time">;
 def _SLASH_MTd : CLFlag<"MTd">, HelpText<"Use static debug run-time">;
 def _SLASH_Tc : CLJoinedOrSeparate<"Tc">, HelpText<"Specify a C source file">,
   MetaVarName<"<filename>">;
 def _SLASH_TC : CLFlag<"TC">, HelpText<"Treat all source files as C">;
 def _SLASH_Tp : CLJoinedOrSeparate<"Tp">, HelpText<"Specify a C++ source file">,
   MetaVarName<"<filename>">;
 def _SLASH_TP : CLFlag<"TP">, HelpText<"Treat all source files as C++">;
+def _SLASH_Za : CLFlag<"Za">;
 
 
 // Ignored:
 
 def _SLASH_analyze_ : CLIgnoredFlag<"analyze-">;
 def _SLASH_errorReport : CLIgnoredJoined<"errorReport">;
 def _SLASH_nologo : CLIgnoredFlag<"nologo">;
 def _SLASH_Ob1 : CLIgnoredFlag<"Ob1">;

lib/Driver/Tools.cpp

case options::OPT__SLASH_MTd:
       CmdArgs.push_back("-D_DEBUG");
       CmdArgs.push_back("-D_MT");
       CmdArgs.push_back("--dependent-lib=libcmtd");
       break;
     default:
       llvm_unreachable("Unexpected option ID.");
   }
 
-  // This provides POSIX compatibility (maps 'open' to '_open'), which most users
-  // want.  MSVC has a switch to turn off this autolinking, but it's not
-  // implemented in clang yet.
+  if (!Args.hasArg(options::OPT__SLASH_Za)) {
+    // This provides POSIX compatibility (maps 'open' to '_open'),
+    // which most users want.
     CmdArgs.push_back("--dependent-lib=oldnames");
   }
+}
 
 void ClangAs::ConstructJob(Compilation &C, const JobAction &JA,
                            const InputInfo &Output,
                            const InputInfoList &Inputs,
                            const ArgList &Args,
                            const char *LinkingOutput) const {
   ArgStringList CmdArgs;
 

test/Driver/cl-Za.c

+// Don't attempt slash switches on msys bash.
+// REQUIRES: shell-preserves-root
+
+// 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 -### -- %s 2>&1 | FileCheck -check-prefix=DEFAULT %s
+// DEFAULT: "--dependent-lib=oldnames"
+
+// RUN: %clang_cl /Za -### -- %s 2>&1 | FileCheck -check-prefix=Za %s
+// Za-NOT: "--dependent-lib=oldnames"