extract get_dependencies method

Summary:
A number of places were extracting dependencies from manifests, but only one was adding in the implicit dependencies for build tools.

Extract the logic to one place and use so that a change in a tool like cmake will now correctly affect all tools using cmake, as it will be taken into account as a dependency hash when the manifest's hash is computed.

Tests for this change revealed that install_dirs needed to be populated in reverse order from the manifest topo-sort, so have also addressed that

Reviewed By: wittgenst

Differential Revision: D32730717

fbshipit-source-id: 1b2a25e460de6085d274c99acfd391b3bd259264

build/fbcode_builder/getdeps.py

@@ -581,7 +581,10 @@ class BuildCmd(ProjectCmdBase):
                 elif args.verbose:
                     print("found good %s" % built_marker)
 
-            install_dirs.append(inst_dir)
+            # Paths are resolved from front. We prepend rather than append as
+            # the last project in topo order is the project itself, which
+            # should be first in the path, then its deps and so on.
+            install_dirs.insert(0, inst_dir)
 
     def compute_dep_change_status(self, m, built_marker, loader):
         reconfigure = False
@@ -589,7 +592,7 @@ class BuildCmd(ProjectCmdBase):
         st = os.lstat(built_marker)
 
         ctx = loader.ctx_gen.get_context(m.name)
-        dep_list = sorted(m.get_section_as_dict("dependencies", ctx).keys())
+        dep_list = m.get_dependencies(ctx)
         for dep in dep_list:
             if reconfigure and sources_changed:
                 break