move project hash computation to ManifestLoader

Summary:
Move code that computes project hashes to ManifestLoader.  ManifestLoader is
the only class that has all of the information necessary to compute the
project hashes correctly.  The ManifestLoader object can also cache previously
computed hashes, so that we don't have to keep computing hashes for projects
over and over again.  Previously the `BuildOptions.compute_dirs()` function
would end up re-computing hashes for all dependencies each time it was called.

Reviewed By: strager

Differential Revision: D16477401

fbshipit-source-id: ce03642114f91ce4f859f612e6b2e747cf1653be

build/fbcode_builder/getdeps/load.py

@@ -7,9 +7,12 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
+import base64
 import glob
+import hashlib
 import os
 
+from .envfuncs import path_search
 from .manifest import ManifestParser
 
 
@@ -101,6 +104,7 @@ class ManifestLoader(object):
 
         self.manifests_by_name = {}
         self._loaded_all = False
+        self._project_hashes = {}
 
     def load_manifest(self, name):
         manifest = self.manifests_by_name.get(name)
@@ -191,3 +195,74 @@ class ManifestLoader(object):
     def create_fetcher(self, manifest):
         ctx = self.ctx_gen.get_context(manifest.name)
         return manifest.create_fetcher(self.build_opts, ctx)
+
+    def get_project_hash(self, manifest):
+        h = self._project_hashes.get(manifest.name)
+        if h is None:
+            h = self._compute_project_hash(manifest)
+            self._project_hashes[manifest.name] = h
+        return h
+
+    def _compute_project_hash(self, manifest):
+        """ This recursive function computes a hash for a given manifest.
+        The hash takes into account some environmental factors on the
+        host machine and includes the hashes of its dependencies.
+        No caching of the computation is performed, which is theoretically
+        wasteful but the computation is fast enough that it is not required
+        to cache across multiple invocations. """
+        hasher = hashlib.sha256()
+        # Some environmental and configuration things matter
+        env = {}
+        env["install_dir"] = self.build_opts.install_dir
+        env["scratch_dir"] = self.build_opts.scratch_dir
+        env["os"] = self.build_opts.host_type.ostype
+        env["distro"] = self.build_opts.host_type.distro
+        env["distro_vers"] = self.build_opts.host_type.distrovers
+        for name in ["CXXFLAGS", "CPPFLAGS", "LDFLAGS", "CXX", "CC"]:
+            env[name] = os.environ.get(name)
+        for tool in ["cc", "c++", "gcc", "g++", "clang", "clang++"]:
+            env["tool-%s" % tool] = path_search(os.environ, tool)
+
+        fetcher = self.create_fetcher(manifest)
+        env["fetcher.hash"] = fetcher.hash()
+
+        for name in sorted(env.keys()):
+            hasher.update(name.encode("utf-8"))
+            value = env.get(name)
+            if value is not None:
+                hasher.update(value.encode("utf-8"))
+
+        ctx = self.ctx_gen.get_context(manifest.name)
+        manifest.update_hash(hasher, ctx)
+
+        dep_list = sorted(manifest.get_section_as_dict("dependencies", ctx).keys())
+        for dep in dep_list:
+            dep_manifest = self.load_manifest(dep)
+            dep_hash = self.get_project_hash(dep_manifest)
+            hasher.update(dep_hash.encode("utf-8"))
+
+        # Use base64 to represent the hash, rather than the simple hex digest,
+        # so that the string is shorter.  Use the URL-safe encoding so that
+        # the hash can also be safely used as a filename component.
+        h = base64.urlsafe_b64encode(hasher.digest()).decode("ascii")
+        # ... and because cmd.exe is troublesome with `=` signs, nerf those.
+        # They tend to be padding characters at the end anyway, so we can
+        # safely discard them.
+        h = h.replace("=", "")
+
+        return h
+
+    def _get_project_dir_name(self, manifest):
+        if manifest.is_first_party_project():
+            return manifest.name
+        else:
+            project_hash = self.get_project_hash(manifest)
+            return "%s-%s" % (manifest.name, project_hash)
+
+    def get_project_install_dir(self, manifest):
+        project_dir_name = self._get_project_dir_name(manifest)
+        return os.path.join(self.build_opts.install_dir, project_dir_name)
+
+    def get_project_build_dir(self, manifest):
+        project_dir_name = self._get_project_dir_name(manifest)
+        return os.path.join(self.build_opts.scratch_dir, "build", project_dir_name)