C_INCLUDE_DIRS, when adding a relative path, fixes joining sysroot to the relative path.

[lancethepants]

Summary

Fixes an issue where adding a relative path to the C include Directories via the C_INCLUDE_DIRS compile time option, there is a "/" ommitted to join the sysroot and the supplied relative path. Sysroot is not expected to have a trailing "/", and...

clang/lib/Driver/ToolChains/Darwin.cpp

if (NoStdInc || NoStdlibInc)
     return;
 
   // Check for configure-time C include directories.
   llvm::StringRef CIncludeDirs(C_INCLUDE_DIRS);
   if (!CIncludeDirs.empty()) {
     llvm::SmallVector<llvm::StringRef, 5> dirs;
     CIncludeDirs.split(dirs, ":");
     for (llvm::StringRef dir : dirs) {
-      llvm::StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : llvm::StringRef(Sysroot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
+      if (llvm::sys::path::is_absolute(dir))
+        addExternCSystemInclude(DriverArgs, CC1Args, dir);
+      else {
+        addExternCSystemInclude(DriverArgs, CC1Args,
+                                StringRef(Sysroot) + "/" + dir);
+      }
     }
   } else {
     // Otherwise, add <sysroot>/usr/include.
     SmallString<128> P(Sysroot);
     llvm::sys::path::append(P, "usr", "include");
     addExternCSystemInclude(DriverArgs, CC1Args, P.str());
   }
 }

clang/lib/Driver/ToolChains/Fuchsia.cpp

if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
   // Check for configure-time C include directories.
   StringRef CIncludeDirs(C_INCLUDE_DIRS);
   if (CIncludeDirs != "") {
     SmallVector<StringRef, 5> dirs;
     CIncludeDirs.split(dirs, ":");
     for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : StringRef(D.SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
+      if (llvm::sys::path::is_absolute(dir))
+        addExternCSystemInclude(DriverArgs, CC1Args, dir);
+      else {
+        addExternCSystemInclude(DriverArgs, CC1Args,
+                                StringRef(D.SysRoot) + "/" + dir);
+      }
     }
     return;
   }
 
   if (!D.SysRoot.empty()) {
     SmallString<128> P(D.SysRoot);
     llvm::sys::path::append(P, "include");
     addExternCSystemInclude(DriverArgs, CC1Args, P.str());

clang/lib/Driver/ToolChains/Hurd.cpp

if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
   // Check for configure-time C include directories.
   StringRef CIncludeDirs(C_INCLUDE_DIRS);
   if (CIncludeDirs != "") {
     SmallVector<StringRef, 5> Dirs;
     CIncludeDirs.split(Dirs, ":");
     for (StringRef Dir : Dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(Dir) ? "" : StringRef(SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + Dir);
+      if (llvm::sys::path::is_absolute(Dir))
+        addExternCSystemInclude(DriverArgs, CC1Args, Dir);
+      else {
+        addExternCSystemInclude(DriverArgs, CC1Args,
+                                StringRef(SysRoot) + "/" + Dir);
+      }
     }
     return;
   }
 
   // Lacking those, try to detect the correct set of system includes for the
   // target triple.
 
   AddMultilibIncludeArgs(DriverArgs, CC1Args);

clang/lib/Driver/ToolChains/Linux.cpp

if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
   // Check for configure-time C include directories.
   StringRef CIncludeDirs(C_INCLUDE_DIRS);
   if (CIncludeDirs != "") {
     SmallVector<StringRef, 5> dirs;
     CIncludeDirs.split(dirs, ":");
     for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : StringRef(SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
+      if (llvm::sys::path::is_absolute(dir))
+        addExternCSystemInclude(DriverArgs, CC1Args, dir);
+      else {
+        addExternCSystemInclude(DriverArgs, CC1Args,
+                                StringRef(SysRoot) + "/" + dir);
+      }
     }
     return;
   }
 
   // Lacking those, try to detect the correct set of system includes for the
   // target triple.
 
   AddMultilibIncludeArgs(DriverArgs, CC1Args);

clang/lib/Driver/ToolChains/OpenBSD.cpp

if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
   // Check for configure-time C include directories.
   StringRef CIncludeDirs(C_INCLUDE_DIRS);
   if (CIncludeDirs != "") {
     SmallVector<StringRef, 5> dirs;
     CIncludeDirs.split(dirs, ":");
     for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? StringRef(D.SysRoot) : "";
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
+      if (llvm::sys::path::is_absolute(dir))
+        addExternCSystemInclude(DriverArgs, CC1Args, dir);
+      else {
+        addExternCSystemInclude(DriverArgs, CC1Args,
+                                StringRef(D.SysRoot) + "/" + dir);
+      }
     }
     return;
   }
 
   addExternCSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/usr/include");
 }
 
 void OpenBSD::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,

clang/lib/Driver/ToolChains/Solaris.cpp

if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
   // Check for configure-time C include directories.
   StringRef CIncludeDirs(C_INCLUDE_DIRS);
   if (CIncludeDirs != "") {
     SmallVector<StringRef, 5> dirs;
     CIncludeDirs.split(dirs, ":");
     for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : StringRef(D.SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
+      if (llvm::sys::path::is_absolute(dir))
+        addExternCSystemInclude(DriverArgs, CC1Args, dir);
+      else {
+        addExternCSystemInclude(DriverArgs, CC1Args,
+                                StringRef(D.SysRoot) + "/" + dir);
+      }
     }
     return;
   }
 
   // Add include directories specific to the selected multilib set and multilib.
   if (GCCInstallation.isValid()) {
     const MultilibSet::IncludeDirsFunc &Callback =
         Multilibs.includeDirsCallback();

clang/lib/Driver/ToolChains/WebAssembly.cpp

if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
   // Check for configure-time C include directories.
   StringRef CIncludeDirs(C_INCLUDE_DIRS);
   if (CIncludeDirs != "") {
     SmallVector<StringRef, 5> dirs;
     CIncludeDirs.split(dirs, ":");
     for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : StringRef(D.SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
+      if (llvm::sys::path::is_absolute(dir))
+        addExternCSystemInclude(DriverArgs, CC1Args, dir);
+      else {
+        addExternCSystemInclude(DriverArgs, CC1Args,
+                                StringRef(D.SysRoot) + "/" + dir);
+      }
     }
     return;
   }
 
   if (getTriple().getOS() != llvm::Triple::UnknownOS) {
     const std::string MultiarchTriple =
         getMultiarchTriple(D, getTriple(), D.SysRoot);
     addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include/" + MultiarchTriple);