getdeps: allow overriding project source, build, and install directories

Summary:
Add arguments to getdeps.py to allow overriding the source, build, and install
directories a per-project basis.  The arguments take the form `[PROJECT:]PATH`
If the `PROJECT` portion is omitted, it defaults to the current project being
built.

In particular this makes it possible to specify `--src-dir .` to tell
getdeps.py to find the project sources from the current directory rather than
downloading them.

Reviewed By: wez

Differential Revision: D16778011

fbshipit-source-id: f33b87213ace04abb66334f588babdf59df91964

build/fbcode_builder/getdeps/fetcher.py

@@ -130,6 +130,26 @@ class Fetcher(object):
         pass
 
 
+class LocalDirFetcher(object):
+    """ This class exists to override the normal fetching behavior, and
+    use an explicit user-specified directory for the project sources.
+
+    This fetcher cannot update or track changes.  It always reports that the
+    project has changed, forcing it to always be built. """
+
+    def __init__(self, path):
+        self.path = os.path.realpath(path)
+
+    def update(self):
+        return ChangeStatus(all_changed=True)
+
+    def hash(self):
+        return "0" * 40
+
+    def get_src_dir(self):
+        return self.path
+
+
 class GitFetcher(Fetcher):
     DEFAULT_DEPTH = 100