[clang] [clang] Support --sysroot= for ${arch}-windows-msvc targets (PR #96417)

[Yaxun Liu via cfe-commits]

================
@@ -1216,3 +1363,121 @@ void MSVCToolChain::addClangTargetOptions(
   if (Arg *A = DriverArgs.getLastArgNoClaim(options::OPT_marm64x))
     A->ignoreTargetSpecific();
 }
+
+void MSVCToolChain::addMsvcstlIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
+  const Driver &D = getDriver();
+  std::string SysRoot = computeSysRoot();
+  std::string LibPath = SysRoot + "/include";
+  const std::string MultiarchTriple =
+      getMultiarchTriple(D, getTripleWithUnknownVendor(*this), SysRoot);
+
+  std::string TargetDir = LibPath + "/" + MultiarchTriple + "/c++/msvcstl";
+  addSystemInclude(DriverArgs, CC1Args, TargetDir);
+
+  // Second add the generic one.
+  addSystemInclude(DriverArgs, CC1Args, LibPath + "/c++/msvcstl");
+}
+
+void MSVCToolChain::addLibCxxIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
+  const Driver &D = getDriver();
+  std::string SysRoot = computeSysRoot();
+  std::string LibPath = SysRoot + "/include";
+  const std::string MultiarchTriple =
+      getMultiarchTriple(D, getTripleWithUnknownVendor(*this), SysRoot);
+
+  std::string Version = detectLibcxxVersion(LibPath);
+  if (Version.empty())
+    return;
+
+  std::string TargetDir = LibPath + "/" + MultiarchTriple + "/c++/" + Version;
+  addSystemInclude(DriverArgs, CC1Args, TargetDir);
+
+  // Second add the generic one.
+  addSystemInclude(DriverArgs, CC1Args, LibPath + "/c++/" + Version);
+}
+
+void MSVCToolChain::addLibStdCXXIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
+  // We cannot use GCCInstallationDetector here as the sysroot usually does
+  // not contain a full GCC installation.
+  // Instead, we search the given sysroot for /usr/include/xx, similar
+  // to how we do it for libc++.
+  const Driver &D = getDriver();
+  std::string SysRoot = computeSysRoot();
+  std::string LibPath = SysRoot + "/include";
+  const std::string MultiarchTriple =
+      getMultiarchTriple(D, getTripleWithUnknownVendor(*this), SysRoot);
+
+  // This is similar to detectLibcxxVersion()
+  std::string Version;
+  {
+    std::error_code EC;
+    Generic_GCC::GCCVersion MaxVersion =
+        Generic_GCC::GCCVersion::Parse("0.0.0");
+    SmallString<128> Path(LibPath);
+    llvm::sys::path::append(Path, "c++");
+    for (llvm::vfs::directory_iterator LI = getVFS().dir_begin(Path, EC), LE;
+         !EC && LI != LE; LI = LI.increment(EC)) {
+      StringRef VersionText = llvm::sys::path::filename(LI->path());
+      if (VersionText[0] != 'v') {
+        auto Version = Generic_GCC::GCCVersion::Parse(VersionText);
+        if (Version > MaxVersion)
+          MaxVersion = Version;
+      }
+    }
+    if (MaxVersion.Major > 0)
+      Version = MaxVersion.Text;
+  }
+
+  if (Version.empty())
+    return;
+
+  std::string TargetDir = LibPath + "/c++/" + Version + "/" + MultiarchTriple;
+  addSystemInclude(DriverArgs, CC1Args, TargetDir);
+
+  // Second add the generic one.
+  addSystemInclude(DriverArgs, CC1Args, LibPath + "/c++/" + Version);
+  // Third the backward one.
+  addSystemInclude(DriverArgs, CC1Args,
+                   LibPath + "/c++/" + Version + "/backward");
+}
+
+llvm::SmallVector<std::string> MSVCToolChain::getCXXStdlibIncludeDirs(
+    const llvm::opt::ArgList &DriverArgs) const {
+  auto cxxStdlibType = GetCXXStdlibType(DriverArgs);
+  if (cxxStdlibType == ToolChain::CST_MSVCSTL) {
+    llvm::SmallVector<std::string> vec;
+    if (DriverArgs.hasArg(options::OPT_nostdinc, options::OPT_nostdlibinc))
----------------
yxsamliu wrote:

Could this also handle `-nostdinc++`? Before this change, `--print-cxx-stdlib-include-dirs -nostdinc++` printed no paths. The updated test now expects the MSVC include path instead. Please preserve the old behavior and keep the test expecting no output.

https://github.com/llvm/llvm-project/pull/96417