mononoke: change how we generate filenodes for octopus merges

Summary:
In the next diff I'm going to refactor BlobRepo::get_manifest_from_bonsai()
function and remove IncompleteFilenodes structure. While doing so I noticed
that the behaviour of get_manifest_from_bonsai() and FilenodesOnlyPublic is
different with regards to generating hg filenodes for octopus merges. In
particular, get_manifest_from_bonsai() at the moment doesn't generate filenodes
for paths that came from stepparents, but FilenodesOnlyPublic does generate
them.

I'd say both of this approach are equally reasonable, however let's try to
preserve the behaviour

Reviewed By: krallin

Differential Revision: D19856420

fbshipit-source-id: 9f8ae656205f39536c450b885fc4d8d6a2534456

Author: StanislavGlebik

eden/mononoke/derived_data/filenodes/lib.rs

@@ -174,7 +174,7 @@ fn classify_filenode(filenode: FilenodeInfo) -> Either<RootFilenodeInfo, Filenod
     }
 }
 
-async fn generate_all_filenodes(
+pub async fn generate_all_filenodes(
     ctx: &CoreContext,
     repo: &BlobRepo,
     cs_id: ChangesetId,
@@ -184,12 +184,12 @@ async fn generate_all_filenodes(
         .compat()
         .await?;
 
-    // Mercurial commits can have only 2 parents, however bonsai commits can have more
-    // In that case p3, p4, ... are ignored (they are called step parents)
-    let cs_parents: Vec<_> = parents.into_iter().take(2).collect();
     let root_mf = fetch_root_manifest_id(&ctx, &cs_id, &repo);
+    // Bonsai might have > 2 parents, while mercurial supports at most 2.
+    // That's fine for us - we just won't generate filenodes for paths that came from
+    // stepparents. That means that linknode for these filenodes will point to a stepparent
     let parents = try_join_all(
-        cs_parents
+        parents
             .iter()
             .map(|p| fetch_root_manifest_id(&ctx, p, &repo)),
     );
@@ -410,6 +410,7 @@ mod tests {
     use super::*;
     use fbinit::FacebookInit;
     use mononoke_types::FileType;
+    use slog::info;
     use tests_utils::CreateCommitContext;
 
     async fn verify_filenodes(
@@ -540,16 +541,18 @@ mod tests {
             .commit()
             .await?;
 
-        // Root filenode was changed, and all files from p3 were added (because parents beyond
-        // p1 an p2 are ignored when generating filenodes and hg changesets)
+        info!(ctx.logger(), "checking filenodes for {}", p3);
         verify_filenodes(
             &ctx,
             &repo,
-            merge,
+            p3,
             vec![RepoPath::RootPath, RepoPath::file("path3")?],
         )
         .await?;
 
+        info!(ctx.logger(), "checking filenodes for {}", merge);
+        verify_filenodes(&ctx, &repo, merge, vec![RepoPath::RootPath]).await?;
+
         Ok(())
     }