add tests for Rust rollout config

Summary:
# Context

Our last attempt at removing the Python version of `eden redirect` failed (see the SEV attached to D55426809). Our next attempt should be done in a phased manner to avoid similar breakages.

# Solution

We will slowly remove all possible fallbacks to Python so that we can be sure no commands are running the Python version of `eden redirect` prior to deleting the code. New rollout plan is as follows:

1) Remove the Chef recipe that writes `/etc/eden/edenfsctl_rollout.json` (Done)
2) Remove "redirect" from the default list of experimental commands in the Rust code.
3) Add a fallback to Rust if Python parsing fails for experimental commands
4) Add an EdenFS event that's logged every time we fallback to the Python `eden redirect` codepath
5) Monitor Scuba data to ensure the Python codepath isn't being hit
6) Delete Python `eden redirect` altogether

# This diff

Adds tests to verify that the new logic from #3 (and old existing logic for rollouts) works as expected.

Reviewed By: kmancini

Differential Revision: D56331275

fbshipit-source-id: 369242d1343b58d78d05dcd41847430ae7304569

Author: MichaelCuevas

eden/fs/cli/main.py

@@ -1326,7 +1326,7 @@ def run(self, args: argparse.Namespace) -> int:
 class PrefetchProfileCmd(Subcmd):
     def run(self, args: argparse.Namespace) -> int:
         print_stderr("This is not implemented for python edenfsctl.")
-        return 1
+        return EX_USAGE
 
 
 @subcmd("fsck", "Perform a filesystem check for EdenFS")

eden/integration/config_test.py

@@ -6,6 +6,7 @@
 
 # pyre-unsafe
 
+import subprocess
 import time
 from pathlib import Path
 
@@ -164,3 +165,50 @@ def assert_current_interval(expected: str) -> None:
         write_user_config("bogus value")
         time.sleep(0.200)
         assert_current_interval(default_interval)
+
+
+@testcase.eden_repo_test
+class RustRolloutConfigTest(testcase.EdenRepoTest):
+    def populate_repo(self) -> None:
+        self.repo.write_file("hello", "hola\n")
+        self.repo.commit("Initial commit.")
+
+    def test_fallback_to_rust(self) -> None:
+        # Testing the case where we fallback to Rust because a command marked
+        # as "experimental" doesn't actually exist in Python.
+        self.set_rust_rollout_config({"prefetch-profile": False})
+        res = self.eden.run_cmd(
+            "prefetch-profile", "list", "--checkout", f"{self.mount}"
+        )
+        self.assertIn("No active prefetch profiles.", res)
+
+        # If EDENFSCTL_SKIP_RUST is set, we shouldn't try to fallback to Rust
+        with self.assertRaises(subprocess.CalledProcessError):
+            self.eden.run_cmd(
+                "prefetch-profile",
+                "list",
+                "--checkout",
+                f"{self.mount}",
+                env={"EDENFSCTL_SKIP_RUST": "1"},
+            )
+
+        # If EDENFSCTL_ONLY_RUST is set, ignore the rollout config
+        res = self.eden.run_cmd(
+            "prefetch-profile",
+            "list",
+            "--checkout",
+            f"{self.mount}",
+            env={"EDENFSCTL_ONLY_RUST": "1"},
+        )
+        self.assertIn("No active prefetch profiles.", res)
+
+        # If EDENFSCTL_SKIP_RUST is set, ignore the rollout config
+        self.set_rust_rollout_config({"prefetch-profile": True})
+        with self.assertRaises(subprocess.CalledProcessError):
+            self.eden.run_cmd(
+                "prefetch-profile",
+                "list",
+                "--checkout",
+                f"{self.mount}",
+                env={"EDENFSCTL_SKIP_RUST": "1"},
+            )