watchman: pass version info down to watchman build via environment

Summary:
This diff allows passing a watchman version number override
via the environment as well as via the cmake `WATCHMAN_VERSION_OVERRIDE`
option.

To help invalidate the build I've added a new section to the manifest
files that allows listing out additional env vars that the project
hashes should be sensitive to.  The effect of this is that we'll
re-run the cmake configure step if the listed env vars are changed.

Reviewed By: Ben0mega

Differential Revision: D17865896

fbshipit-source-id: 8ea5572b0b9b7af95ec5c310e494cb17a139ced4

build/fbcode_builder/getdeps/load.py

@@ -260,6 +260,8 @@ class ManifestLoader(object):
         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. """
+        ctx = self.ctx_gen.get_context(manifest.name)
+
         hasher = hashlib.sha256()
         # Some environmental and configuration things matter
         env = {}
@@ -272,6 +274,8 @@ class ManifestLoader(object):
             env[name] = os.environ.get(name)
         for tool in ["cc", "c++", "gcc", "g++", "clang", "clang++"]:
             env["tool-%s" % tool] = path_search(os.environ, tool)
+        for name in manifest.get_section_as_args("depends.environment", ctx):
+            env[name] = os.environ.get(name)
 
         fetcher = self.create_fetcher(manifest)
         env["fetcher.hash"] = fetcher.hash()
@@ -282,7 +286,6 @@ class ManifestLoader(object):
             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())

build/fbcode_builder/getdeps/manifest.py

@@ -49,6 +49,7 @@ SCHEMA = {
         },
     },
     "dependencies": {"optional_section": True, "allow_values": False},
+    "depends.environment": {"optional_section": True},
     "git": {
         "optional_section": True,
         "fields": {"repo_url": REQUIRED, "rev": OPTIONAL, "depth": OPTIONAL},

build/fbcode_builder/manifests/watchman

@@ -34,3 +34,6 @@ ENABLE_EDEN_SUPPORT=ON
 WATCHMAN_STATE_DIR=/opt/facebook/watchman/var/run/watchman
 # tell cmake not to try to create /opt/facebook/...
 INSTALL_WATCHMAN_STATE_DIR=OFF
+
+[depends.environment]
+WATCHMAN_VERSION_OVERRIDE