darwin/driver: Support using SDKROOT to define the default for -isysroot.

 - The SDKROOT environment variable is the de facto way to set the default SDK
   for a number of tools, join forces with them.

llvm-svn: 162116

1 files changed, 14 insertions, 0 deletions

diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index 01c66239a12..5cf97b702b3 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -442,6 +442,20 @@ static bool GetVersionFromSimulatorDefine(StringRef define,
 void Darwin::AddDeploymentTarget(DerivedArgList &Args) const {
   const OptTable &Opts = getDriver().getOpts();
 
+  // Support allowing the SDKROOT environment variable used by xcrun and other
+  // Xcode tools to define the default sysroot, by making it the default for
+  // isysroot.
+  if (!Args.hasArg(options::OPT_isysroot)) {
+    if (char *env = ::getenv("SDKROOT")) {
+      // We only use this value as the default if it is an absolute path and
+      // exists.
+      if (llvm::sys::path::is_absolute(env) && llvm::sys::fs::exists(env)) {
+        Args.append(Args.MakeSeparateArg(
+                      0, Opts.getOption(options::OPT_isysroot), env));
+      }
+    }
+  }
+
   Arg *OSXVersion = Args.getLastArg(options::OPT_mmacosx_version_min_EQ);
   Arg *iOSVersion = Args.getLastArg(options::OPT_miphoneos_version_min_EQ);
   Arg *iOSSimVersion = Args.getLastArg(