report file changes on fresh instance

Summary: Actual fix of the bug. Watchman checks `disable_watchman_empty_on_fresh_instance` config setting, but it's rolled out 100%, so report changes in edenfs unconditionally.

Reviewed By: jdelliot

Differential Revision: D69791442

fbshipit-source-id: 951a5a069f41e06b9f6a6363f43abdb4811a94d2

app/buck2_file_watcher/src/edenfs/interface.rs

@@ -542,28 +542,37 @@ impl EdenFsFileWatcher {
         let dice = dice.unstable_take();
 
         // Get mergebase state
-        let last_mergebase = self.last_mergebase.read().await.clone();
-        let mergebase = self.mergebase.read().await.clone();
-        let branched_from_revision_timestamp = mergebase.as_ref().map(|m| m.timestamp);
-        let branched_from_global_rev = mergebase.as_ref().and_then(|m| m.global_rev);
+        let last_mergebase_info = self.last_mergebase.read().await.clone();
+        let mergebase_info = self.mergebase.read().await.clone();
+        let mergebase = mergebase_info.as_ref().map(|m| m.mergebase.clone());
+        let branched_from_revision_timestamp = mergebase_info.as_ref().map(|m| m.timestamp);
+        let branched_from_global_rev = mergebase_info.as_ref().and_then(|m| m.global_rev);
 
         let mut base_stats = buck2_data::FileWatcherStats {
             fresh_instance: true,
-            branched_from_revision: mergebase.as_ref().map(|m| m.mergebase.clone()),
+            branched_from_revision: mergebase.clone(),
             branched_from_global_rev,
             branched_from_revision_timestamp,
             watchman_version: None,
             fresh_instance_data: Some(buck2_data::FreshInstance {
-                new_mergebase: last_mergebase.is_none() || last_mergebase != mergebase,
+                new_mergebase: last_mergebase_info.is_none()
+                    || last_mergebase_info != mergebase_info,
                 cleared_dice: true,
                 cleared_dep_files: true,
             }),
             ..Default::default()
         };
 
-        base_stats.incomplete_events_reason = Some("Large or Unknown change".to_owned());
-
-        Ok((FileWatcherStats::new(base_stats, 0), dice))
+        if let Some(mergebase) = mergebase {
+            let mut tracker = FileChangeTracker::new();
+            let mut stats = FileWatcherStats::new(base_stats, 0);
+            self.process_sapling_status(&mut tracker, &mut stats, mergebase, None)
+                .await?;
+            Ok((stats, dice))
+        } else {
+            base_stats.incomplete_events_reason = Some("Large or Unknown change".to_owned());
+            Ok((FileWatcherStats::new(base_stats, 0), dice))
+        }
     }
 
     // Compute and update the mergebase.

tests/core/io/test_edenfs.py

@@ -10,9 +10,13 @@
 import subprocess
 
 from buck2.tests.core.common.io.file_watcher import (
+    FileWatcherEvent,
+    FileWatcherEventType,
+    FileWatcherKind,
     FileWatcherProvider,
     get_file_watcher_events,
 )
+
 from buck2.tests.core.common.io.file_watcher_dir_tests import (
     run_create_directory_test,
     run_remove_directory_test,
@@ -35,6 +39,7 @@
 from buck2.tests.core.common.io.file_watcher_tests import (
     FileSystemType,
     setup_file_watcher_test,
+    verify_results,
 )
 
 from buck2.tests.e2e_util.api.buck import Buck
@@ -164,7 +169,15 @@ async def test_edenfs_files_report_on_fresh_instance(buck: Buck) -> None:
     await setup_file_watcher_scm_test(buck)
     await buck.kill()
 
+    required = [
+        FileWatcherEvent(
+            FileWatcherEventType.CREATE, FileWatcherKind.FILE, "root//files/ghi"
+        ),
+        FileWatcherEvent(
+            FileWatcherEventType.CREATE, FileWatcherKind.FILE, "root//files/jkl"
+        ),
+    ]
+
     is_fresh_instance, results = await get_file_watcher_events(buck)
     assert is_fresh_instance
-    # this is a bug, we should report file changes
-    assert results == []
+    verify_results(results, required)