clang-cl: Remove -isystem, add -imsvc.

r260990 exposed -isystem in clang-cl. -isystem adds a directory to the front of
the system include search path. The idea was to use this to point to a hermetic
msvc install, but as it turns out this doesn't work: -isystem then adds the
hermetic headers in front of clang's builtin headers, and clang's headers that
are supposed to wrap msvc headers (say, stdarg.h) aren't picked up at all
anymore.

So revert that, and instead expose -imsvc which works as if the passed
directory was part of %INCLUDE%: The header is treated as a system header, but
it is searched after clang's lib/Header headers.

Fixes half of PRPR26751.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@266108 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Driver/CLCompatOptions.td

@@ -210,6 +210,9 @@ def _SLASH_GX : CLFlag<"GX">,
   HelpText<"Enable exception handling">;
 def _SLASH_GX_ : CLFlag<"GX-">,
   HelpText<"Enable exception handling">;
+def _SLASH_imsvc : CLJoinedOrSeparate<"imsvc">,
+  HelpText<"Add directory to system include search path, as if part of %INCLUDE%">,
+  MetaVarName<"<dir>">;
 def _SLASH_LD : CLFlag<"LD">, HelpText<"Create DLL">;
 def _SLASH_LDd : CLFlag<"LDd">, HelpText<"Create debug DLL">;
 def _SLASH_link : CLRemainingArgs<"link">,

include/clang/Driver/Options.td

@@ -1254,7 +1254,7 @@ def iquote : JoinedOrSeparate<["-"], "iquote">, Group<clang_i_Group>, Flags<[CC1
 def isysroot : JoinedOrSeparate<["-"], "isysroot">, Group<clang_i_Group>, Flags<[CC1Option]>,
   HelpText<"Set the system root directory (usually /)">, MetaVarName<"<dir>">;
 def isystem : JoinedOrSeparate<["-"], "isystem">, Group<clang_i_Group>,
-  Flags<[CC1Option, CoreOption]>,
+  Flags<[CC1Option]>,
   HelpText<"Add directory to SYSTEM include search path">, MetaVarName<"<directory>">;
 def iwithprefixbefore : JoinedOrSeparate<["-"], "iwithprefixbefore">, Group<clang_i_Group>,
   HelpText<"Set directory to include search path with prefix">, MetaVarName<"<dir>">,

lib/Driver/MSVCToolChain.cpp

@@ -527,6 +527,10 @@ void MSVCToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                   "include");
   }
 
+  // Add %INCLUDE%-like directories from the -imsvc flag.
+  for (const auto &Path : DriverArgs.getAllArgValues(options::OPT__SLASH_imsvc))
+    addSystemInclude(DriverArgs, CC1Args, Path);
+
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 

test/Driver/cl-options.c

@@ -82,6 +82,12 @@
 // RUN: %clang_cl /I myincludedir -### -- %s 2>&1 | FileCheck -check-prefix=SLASH_I %s
 // SLASH_I: "-I" "myincludedir"
 
+// RUN: %clang_cl /imsvcmyincludedir -### -- %s 2>&1 | FileCheck -check-prefix=SLASH_imsvc %s
+// RUN: %clang_cl /imsvc myincludedir -### -- %s 2>&1 | FileCheck -check-prefix=SLASH_imsvc %s
+// Clang's resource header directory should be first:
+// SLASH_imsvc: "-internal-isystem" "{{[^"]*}}lib{{.}}clang{{[^"]*}}include"
+// SLASH_imsvc: "-internal-isystem" "myincludedir"
+
 // RUN: %clang_cl /J -### -- %s 2>&1 | FileCheck -check-prefix=J %s
 // J: -fno-signed-char
 
@@ -452,7 +458,6 @@
 // RUN:     -fno-ms-compatibility \
 // RUN:     -fms-extensions \
 // RUN:     -fno-ms-extensions \
-// RUN:     -isystem=some/path \
 // RUN:     -mllvm -disable-llvm-optzns \
 // RUN:     -Wunused-variable \
 // RUN:     -fmacro-backtrace-limit=0 \

test/Driver/cl-pch-search.cpp

@@ -4,7 +4,3 @@
 // REQUIRES: x86-registered-target
 // Check that pchfile.h next to to pchfile.cc is found correctly.
 // RUN: %clang_cl -Werror /Ycpchfile.h /FIpchfile.h /c /Fo%t.obj /Fp%t.pch -- %S/Inputs/pchfile.cpp 
-
-// Check that i_group flags other than -include aren't skipped (e.g. -isystem).
-#include "header0.h"
-// RUN: %clang_cl -Werror -isystem%S/Inputs /Yupchfile.h /FIpchfile.h /c /Fo%t.obj /Fp%t.pch -- %s