getdeps must hash patches referenced by the manifest file

Summary:
**Pre-submission checklist**
- [x] I've ran the linters locally and fixed lint errors related to the
files I modified in this PR. You can install the linters by running `pip install -r requirements-dev.txt && pre-commit install`
- [x] `pre-commit run`

If we don’t include patches in the hash then we won’t rebuild the
dependency when the patch changes.

X-link: facebook/fboss#702

Reviewed By: bigfootjon

Differential Revision: D90142693

Pulled By: KevinYakar

fbshipit-source-id: a49e4d04cbcd5490d9280116b8bb2b2457580d43

Author: benoit-nexthop

build/fbcode_builder/getdeps/load.py

@@ -315,6 +315,16 @@ def _compute_project_hash(self, manifest) -> str:
 
         manifest.update_hash(hasher, ctx)
 
+        # If a patchfile is specified, include its contents in the hash
+        patchfile = manifest.get("build", "patchfile", ctx=ctx)
+        if patchfile:
+            patchfile_path = os.path.join(
+                self.build_opts.fbcode_builder_dir, "patches", patchfile
+            )
+            if os.path.exists(patchfile_path):
+                with open(patchfile_path, "rb") as f:
+                    hasher.update(f.read())
+
         dep_list = manifest.get_dependencies(ctx)
         for dep in dep_list:
             dep_manifest = self.load_manifest(dep)