[Driver] Move detectLibcxxIncludePath to ToolChain

[phosek]

Summary

This helper method is useful even outside of Gnu toolchains, so move
it to ToolChain so it can be reused in other toolchains such as Fuchsia.

[thakis]

Breaks tests on windows: http://45.33.8.238/win/25123/step_7.txt

Please take a look, and revert if it takes a while to fix.

[thakis]

On https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8867483277057489840/+/steps/package_clang/0/stdout?format=raw too. Reverted in ba60dc0aa75e86165e260b2c08afafd1c394e95a for now.

clang/include/clang/Driver/ToolChain.h

public:
   // GetCXXStdlibType - Determine the C++ standard library type to use with the
   // given compilation arguments.
   virtual CXXStdlibType GetCXXStdlibType(const llvm::opt::ArgList &Args) const;
 
   // GetUnwindLibType - Determine the unwind library type to use with the
   // given compilation arguments.
   virtual UnwindLibType GetUnwindLibType(const llvm::opt::ArgList &Args) const;
 
+  // Detect the highest available version of libc++ in base path.
+  virtual std::string
+  detectLibcxxIncludePath(StringRef Base) const;
+
   /// AddClangCXXStdlibIncludeArgs - Add the clang -cc1 level arguments to set
   /// the include paths to use for the given C++ standard library type.
   virtual void
   AddClangCXXStdlibIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                                llvm::opt::ArgStringList &CC1Args) const;
 
   /// AddClangCXXStdlibIsystemArgs - Add the clang -cc1 level arguments to set
   /// the specified include paths for the C++ standard library.

clang/lib/Driver/ToolChain.cpp

/*static*/ void ToolChain::addSystemIncludes(const ArgList &DriverArgs,
                                              ArgStringList &CC1Args,
                                              ArrayRef<StringRef> Paths) {
   for (const auto &Path : Paths) {
     CC1Args.push_back("-internal-isystem");
     CC1Args.push_back(DriverArgs.MakeArgString(Path));
   }
 }
 
+std::string ToolChain::detectLibcxxIncludePath(StringRef Base) const {
+  std::error_code EC;
+  int MaxVersion = 0;
+  std::string MaxVersionString;
+  for (llvm::vfs::directory_iterator LI = getVFS().dir_begin(Base, EC), LE;
+       !EC && LI != LE; LI = LI.increment(EC)) {
+    StringRef VersionText = llvm::sys::path::filename(LI->path());
+    int Version;
+    if (VersionText[0] == 'v' &&
+        !VersionText.slice(1, StringRef::npos).getAsInteger(10, Version)) {
+      if (Version > MaxVersion) {
+        MaxVersion = Version;
+        MaxVersionString = std::string(VersionText);
+      }
+    }
+  }
+  if (!MaxVersion)
+    return "";
+  SmallString<128> P(Base);
+  llvm::sys::path::append(P, MaxVersionString);
+  return std::string(P.str());
+}
+
 void ToolChain::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
                                              ArgStringList &CC1Args) const {
   // Header search paths should be handled by each of the subclasses.
   // Historically, they have not been, and instead have been handled inside of
   // the CC1-layer frontend. As the logic is hoisted out, this generic function
   // will slowly stop being called.
   //
   // While it is being called, replicate a bit of a hack to propagate the

clang/lib/Driver/ToolChains/Fuchsia.cpp

void Fuchsia::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
                                            ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdlibinc) ||
       DriverArgs.hasArg(options::OPT_nostdincxx))
     return;
 
   switch (GetCXXStdlibType(DriverArgs)) {
   case ToolChain::CST_Libcxx: {
     SmallString<128> P(getDriver().Dir);
-    llvm::sys::path::append(P, "..", "include", "c++", "v1");
-    addSystemInclude(DriverArgs, CC1Args, P.str());
+    llvm::sys::path::append(P, "..", "include", "c++");
+    addSystemInclude(DriverArgs, CC1Args, detectLibcxxIncludePath(P.str()));
     break;
   }
 
   default:
     llvm_unreachable("invalid stdlib name");
   }
 }
 

clang/lib/Driver/ToolChains/Gnu.cpp

case ToolChain::CST_Libcxx:
     break;
 
   case ToolChain::CST_Libstdcxx:
     addLibStdCxxIncludePaths(DriverArgs, CC1Args);
     break;
   }
 }
 
-static std::string DetectLibcxxIncludePath(llvm::vfs::FileSystem &vfs,
-                                           StringRef base) {
-  std::error_code EC;
-  int MaxVersion = 0;
-  std::string MaxVersionString;
-  for (llvm::vfs::directory_iterator LI = vfs.dir_begin(base, EC), LE;
-       !EC && LI != LE; LI = LI.increment(EC)) {
-    StringRef VersionText = llvm::sys::path::filename(LI->path());
-    int Version;
-    if (VersionText[0] == 'v' &&
-        !VersionText.slice(1, StringRef::npos).getAsInteger(10, Version)) {
-      if (Version > MaxVersion) {
-        MaxVersion = Version;
-        MaxVersionString = std::string(VersionText);
-      }
-    }
-  }
-  return MaxVersion ? (base + "/" + MaxVersionString).str() : "";
-}
-
 void
 Generic_GCC::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                    llvm::opt::ArgStringList &CC1Args) const {
   auto AddIncludePath = [&](std::string Path) {
-    std::string IncludePath = DetectLibcxxIncludePath(getVFS(), Path);
+    std::string IncludePath = detectLibcxxIncludePath(Path);
     if (IncludePath.empty() || !getVFS().exists(IncludePath))
       return false;
     addSystemInclude(DriverArgs, CC1Args, IncludePath);
     return true;
   };
   // Android never uses the libc++ headers installed alongside the toolchain,
   // which are generally incompatible with the NDK libraries anyway.
   if (!getTriple().isAndroid())