Auto merge of #6306 - metajack:shared-target-dir, r=mbrubeck

This speeds up `./mach build --dev` followed by `./mach build-cef` by
25%. When rust-lang/cargo#497 is fixed, this speedup will increase
dramatically.

<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/6306)
<!-- Reviewable:end -->

1 files changed, 10 insertions, 1 deletions

diff --git a/python/servo/command_base.py b/python/servo/command_base.py
index 5369b3e47f9..c6d46fc3de8 100644
--- a/python/servo/command_base.py
+++ b/python/servo/command_base.py
@@ -130,8 +130,14 @@ class CommandBase(object):
             self._cargo_build_id = open(filename).read().strip()
         return self._cargo_build_id
 
+    def get_target_dir(self):
+        if "CARGO_TARGET_DIR" in os.environ:
+            return os.environ["CARGO_TARGET_DIR"]
+        else:
+            return path.join(self.context.topdir, "target")
+
     def get_binary_path(self, release, dev):
-        base_path = path.join("components", "servo", "target")
+        base_path = self.get_target_dir()
         release_path = path.join(base_path, "release", "servo")
         dev_path = path.join(base_path, "debug", "servo")
 
@@ -199,6 +205,9 @@ class CommandBase(object):
         if "CARGO_HOME" not in env:
             env["CARGO_HOME"] = self.config["tools"]["cargo-home-dir"]
 
+        if "CARGO_TARGET_DIR" not in env:
+            env["CARGO_TARGET_DIR"] = path.join(self.context.topdir, "target")
+
         if extra_lib:
             if sys.platform == "darwin":
                 env["DYLD_LIBRARY_PATH"] = "%s%s%s" % \