pathhistory: fix fetching bug when a path prefix was not a directory

Summary:
When a prefix of the given path was a file (or symlink) in the commit history, the load_tree_entry() will fail,
since it was trying to read a directory.  For example, let's assume the given path is `a/b/c`, and `a/b` is a
directory now; but in the commit history, `a/b` was not a directory (regular file or symlink).

This diff fixes the issue by ignoring the non-directory items, this will make pathhistory ignore those commits
that the prefix was not a directory. If the file was a symlink to another folder, it will not follow the link.

Reviewed By: muirdm

Differential Revision: D67412803

fbshipit-source-id: 5e8ace29e2b26d295f31d3014cb1c67cf98c10e5

eden/scm/lib/pathhistory/src/pathops.rs

@@ -184,6 +184,11 @@ impl<'a> State<'a> {
             None | Some(None) => return Ok(None),
             Some(Some(item)) => item,
         };
+        if item.flag != Flag::Directory {
+            // This happens when the path was a file (or symlink)
+            tracing::debug!("   load_tree_entry: {:?} is not a directory", item);
+            return Ok(None);
+        }
         if item.loaded.is_none() {
             let entry = tree_store.get_content(item.path, item.id, FetchMode::AllowRemote)?;
             let format = tree_store.format();

eden/scm/lib/pathhistory/src/tests.rs

@@ -444,6 +444,24 @@ async fn test_log_dirs() {
     );
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_log_when_a_prefix_was_not_directory() {
+    let t = TestHistory::from_history(&[
+        (0, "a/b", 1, R),
+        (50, "a/b", 0, R),
+        (100, "a/b/c/e", 2, R),
+        (150, "a/b/c/e", 0, R),
+        (200, "h/i/j/k", 5, E),
+        (250, "a/b/c/f", 3, R),
+    ]);
+
+    let mut h = t.paths_history(300, &["a/b/c"]).await;
+    assert_eq!(h.next_n(5).await, [250, 150, 100]);
+
+    let mut h = t.paths_history(300, &["a/b"]).await;
+    assert_eq!(h.next_n(5).await, [250, 150, 100, 50, 0]);
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_log_with_roots() {
     // Use a commit graph with a few roots.