Fix getdeps patch application

Summary: Apply patches from the git repo root so paths resolve correctly even when src_dir is a subdirectory of the repo (e.g. fizz, wangle). Without this, patches with paths relative to the repo root fail to apply.

Reviewed By: bigfootjon

Differential Revision: D93644294

fbshipit-source-id: 5e0006eb988eb4cdc6f0ecb0dae8cb35b7189c5d

Author: afrind

build/fbcode_builder/getdeps/builder.py

@@ -137,7 +137,16 @@ def _apply_patchfile(self) -> None:
             return
         old_wd = os.getcwd()
         os.chdir(self.src_dir)
-        print(f"Patching {self.manifest.name} with {self.patchfile} in {self.src_dir}")
+        # Apply patches from the git repo root so paths resolve correctly
+        # even when src_dir is a subdirectory of the repo.
+        try:
+            git_root = subprocess.check_output(
+                ["git", "rev-parse", "--show-toplevel"], text=True
+            ).strip()
+            os.chdir(git_root)
+        except subprocess.CalledProcessError:
+            pass  # not a git repo, stay in src_dir
+        print(f"Patching {self.manifest.name} with {self.patchfile} in {os.getcwd()}")
         patchfile = os.path.join(
             self.build_opts.fbcode_builder_dir, "patches", self.patchfile
         )