clang-cl: Accept MSVC 2015's `/source-charset:utf-8` flag.

[thakis]

Summary

clang already treats all inputs as utf-8. Warn if anything but utf-8 is passed.

Do this by mapping source-charset to finput-charset, which already behaves like this. Slightly tweak finput-charset to accept "utf-8" case-insensitively. This matches gcc's and cl.exe's behavior, and IANA says that character set names are case-insensitive.

[hans]

lgtm

[thakis]

279531, thanks!

include/clang/Driver/CLCompatOptions.td

def _SLASH_QUESTION : CLFlag<"?">, Alias<help>,
   HelpText<"Display available options">;
 def _SLASH_Qvec : CLFlag<"Qvec">,
   HelpText<"Enable the loop vectorization passes">, Alias<fvectorize>;
 def _SLASH_Qvec_ : CLFlag<"Qvec-">,
   HelpText<"Disable the loop vectorization passes">, Alias<fno_vectorize>;
 def _SLASH_showIncludes : CLFlag<"showIncludes">,
   HelpText<"Print info about included files to stderr">,
   Alias<show_includes>;
+def _SLASH_source_charset : CLCompileJoined<"source-charset:">,
+  HelpText<"Source encoding, supports only UTF-8">, Alias<finput_charset_EQ>;
 def _SLASH_std : CLCompileJoined<"std:">,
   HelpText<"Language standard to compile for">;
 def _SLASH_U : CLJoinedOrSeparate<"U">, HelpText<"Undefine macro">,
   MetaVarName<"<macro>">, Alias<U>;
 def _SLASH_W0 : CLFlag<"W0">, HelpText<"Disable all warnings">, Alias<w>;
 def _SLASH_W1 : CLFlag<"W1">, HelpText<"Enable -Wall">, Alias<Wall>;
 def _SLASH_W2 : CLFlag<"W2">, HelpText<"Enable -Wall">, Alias<Wall>;
 def _SLASH_W3 : CLFlag<"W3">, HelpText<"Enable -Wall">, Alias<Wall>;

lib/Driver/Tools.cpp

   // -fsigned-bitfields is default, and clang doesn't support -fno-for-scope.
   if (!Args.hasFlag(options::OPT_ffor_scope, options::OPT_fno_for_scope))
     D.Diag(diag::err_drv_clang_unsupported)
         << Args.getLastArg(options::OPT_fno_for_scope)->getAsString(Args);
 
   // -finput_charset=UTF-8 is default. Reject others
   if (Arg *inputCharset = Args.getLastArg(options::OPT_finput_charset_EQ)) {
     StringRef value = inputCharset->getValue();
-    if (value != "UTF-8")
+    if (value.lower() != "utf-8")
       D.Diag(diag::err_drv_invalid_value) << inputCharset->getAsString(Args)
                                           << value;
   }
 
   // -fexec_charset=UTF-8 is default. Reject others
   if (Arg *execCharset = Args.getLastArg(options::OPT_fexec_charset_EQ)) {
     StringRef value = execCharset->getValue();
     if (value != "UTF-8")

test/Driver/cl-options.c

 
 // RUN: %clang_cl /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes %s
 // showIncludes: --show-includes
 
 // RUN: %clang_cl /E /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes_E %s
 // RUN: %clang_cl /EP /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes_E %s
 // showIncludes_E: warning: argument unused during compilation: '--show-includes'
 
+// /source-charset: should warn on everything except UTF-8.
+// RUN: %clang_cl /source-charset:utf-16 -### -- %s 2>&1 | FileCheck -check-prefix=source-charset-utf-16 %s
+// source-charset-utf-16: invalid value 'utf-16'
+
 // RUN: %clang_cl /Umymacro -### -- %s 2>&1 | FileCheck -check-prefix=U %s
 // RUN: %clang_cl /U mymacro -### -- %s 2>&1 | FileCheck -check-prefix=U %s
 // U: "-U" "mymacro"
 
 // RUN: %clang_cl /vd2 -### -- %s 2>&1 | FileCheck -check-prefix=VD2 %s
 // VD2: -vtordisp-mode=2
 
 // RUN: %clang_cl /vmg -### -- %s 2>&1 | FileCheck -check-prefix=VMG %s

 // RUN:    /GF \
 // RUN:    /GS- \
 // RUN:    /kernel- \
 // RUN:    /nologo \
 // RUN:    /openmp- \
 // RUN:    /RTC1 \
 // RUN:    /sdl \
 // RUN:    /sdl- \
+// RUN:    /source-charset:utf-8 \
 // RUN:    /vmg \
 // RUN:    /volatile:iso \
 // RUN:    /w12345 \
 // RUN:    /wd1234 \
 // RUN:    /Zo \
 // RUN:    /Zo- \
 // RUN:    -### -- %s 2>&1 | FileCheck -check-prefix=IGNORED %s
 // IGNORED-NOT: argument unused during compilation