[Driver] Set default sysroot for Fuchsia if none is specified

[phosek]

Summary

When sysroot isn't explicitly set, try to use the default location which is <driver path>/../<triple>

[mcgrathr]

lib/Driver/ToolChains/Fuchsia.cpp

152

The GCC behavior (if --with-sysroot is given to configure) is tooldir/sys-root, not tooldir itself.

[phosek]

lib/Driver/ToolChains/Fuchsia.cpp

152

That's fine with me, although I'm not very fond of the sys-root since it's typically spelled as sysroot everywhere else, but I could be convinced if we want to be consistent with GCC.

[mcgrathr]

Is this still live? Should it be different after all the multiarch stuff?

[phosek]

In D42019#1162644, @mcgrathr wrote:

Is this still live? Should it be different after all the multiarch stuff?

I'm about to revive this and was pondering if maybe we should generalize this to all targets now that the multiarch runtime bit has landed?

lib/Driver/ToolChains/Fuchsia.cpp

 
 static std::string getTargetDir(const Driver &D,
                                 llvm::Triple Triple) {
   SmallString<128> P(llvm::sys::path::parent_path(D.Dir));
   llvm::sys::path::append(P, "lib", normalizeTriple(Triple));
   return P.str();
 }
 
+static std::string getSysRoot(const Driver &D, llvm::Triple Triple) {
+  SmallString<128> P(llvm::sys::path::parent_path(D.Dir));
+  llvm::sys::path::append(P, normalizeTriple(Triple));
+  return P.str();
+}
+
 Fuchsia::Fuchsia(const Driver &D, const llvm::Triple &Triple,
                  const ArgList &Args)
     : ToolChain(D, Triple, Args) {
   getProgramPaths().push_back(getDriver().getInstalledDir());
   if (getDriver().getInstalledDir() != D.Dir)
     getProgramPaths().push_back(D.Dir);
 
   SmallString<128> P(getTargetDir(D, getTriple()));
   llvm::sys::path::append(P, "lib");
   getFilePaths().push_back(P.str());
 
-  if (!D.SysRoot.empty()) {
-    SmallString<128> P(D.SysRoot);
-    llvm::sys::path::append(P, "lib");
-    getFilePaths().push_back(P.str());
-  }
+  SmallString<128> S(!D.SysRoot.empty() ? D.SysRoot
+                                        : getSysRoot(D, getTriple()));
+  llvm::sys::path::append(S, "lib");
+  getFilePaths().push_back(S.str());
 }
 
 std::string Fuchsia::ComputeEffectiveClangTriple(const ArgList &Args,
                                                  types::ID InputType) const {
   llvm::Triple Triple(ComputeLLVMTriple(Args, InputType));
   Triple.setTriple(normalizeTriple(Triple));
   return Triple.getTriple();
 }
if (CIncludeDirs != "") {
     for (StringRef dir : dirs) {
       StringRef Prefix =
           llvm::sys::path::is_absolute(dir) ? StringRef(D.SysRoot) : "";
       addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
     }
     return;
   }
 
-  if (!D.SysRoot.empty()) {
-    SmallString<128> P(D.SysRoot);
-    llvm::sys::path::append(P, "include");
-    addExternCSystemInclude(DriverArgs, CC1Args, P.str());
-  }
+  SmallString<128> S(!D.SysRoot.empty() ? D.SysRoot
+                                        : getSysRoot(D, getTriple()));
+  llvm::sys::path::append(S, "include");
+  addExternCSystemInclude(DriverArgs, CC1Args, S.str());
 }
 
 void Fuchsia::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
                                            ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdlibinc) ||
       DriverArgs.hasArg(options::OPT_nostdincxx))
     return;