dag: expose version in namedag states

Summary:
This will be used to detect if the NameDag was changed between reloads,
and decide whether we need to invalidate caches or not.

Reviewed By: andll

Differential Revision: D29888938

fbshipit-source-id: 377879bd8d28c92feca80c025613a65139ccb866

eden/scm/lib/dag/Cargo.toml

@@ -37,6 +37,7 @@ minibytes = { path = "../minibytes" }
 nonblocking = { path = "../nonblocking" }
 parking_lot = "0.10.2"
 quickcheck = { version = "0.9", optional = true }
+rand = { version = "0.7", features = ["small_rng"] }
 serde = { version = "1.0.126", features = ["derive", "rc"] }
 tempfile = { version = "3.1", optional = true }
 thiserror = "1.0"

eden/scm/lib/dag/src/namedag/indexedlog_namedag.rs

@@ -10,6 +10,7 @@ use crate::errors::bug;
 use crate::iddag::IdDag;
 use crate::iddagstore::IndexedLogStore;
 use crate::idmap::IdMap;
+use crate::ops::IntVersion;
 use crate::ops::Open;
 use crate::ops::Persist;
 use crate::ops::TryClone;
@@ -119,6 +120,15 @@ impl Persist for NameDagState {
     }
 }
 
+impl IntVersion for NameDagState {
+    fn int_version(&self) -> (u64, u64) {
+        match &self.mlog {
+            Some(mlog) => mlog.version(),
+            None => (0, 0),
+        }
+    }
+}
+
 impl TryClone for NameDagState {
     fn try_clone(&self) -> Result<Self> {
         Ok(Self {

eden/scm/lib/dag/src/namedag/mem_namedag.rs

@@ -9,6 +9,7 @@ use super::AbstractNameDag;
 use crate::iddag::IdDag;
 use crate::iddagstore::InProcessStore;
 use crate::idmap::MemIdMap;
+use crate::ops::IntVersion;
 use crate::ops::Open;
 use crate::ops::Persist;
 use crate::Id;
@@ -28,7 +29,17 @@ pub type MemNameDag =
 pub struct MemNameDagPath;
 
 #[derive(Debug, Clone)]
-pub struct MemNameDagState;
+pub struct MemNameDagState {
+    version: (u64, u64),
+}
+
+impl Default for MemNameDagState {
+    fn default() -> Self {
+        Self {
+            version: (rand::random(), 0),
+        }
+    }
+}
 
 impl Open for MemNameDagPath {
     type OpenTarget = MemNameDag;
@@ -42,7 +53,7 @@ impl Open for MemNameDagPath {
             path: self.clone(),
             snapshot: Default::default(),
             pending_heads: Default::default(),
-            state: MemNameDagState,
+            state: MemNameDagState::default(),
             id: format!("mem:{}", next_id()),
             overlay_map: Default::default(),
             overlay_map_next_id: Id::MIN,
@@ -72,10 +83,17 @@ impl Persist for MemNameDagState {
     }
 
     fn persist(&mut self, _lock: &Self::Lock) -> Result<()> {
+        self.version.1 += 1;
         Ok(())
     }
 }
 
+impl IntVersion for MemNameDagState {
+    fn int_version(&self) -> (u64, u64) {
+        self.version
+    }
+}
+
 fn next_id() -> u64 {
     static ID: AtomicU64 = AtomicU64::new(0);
     ID.fetch_add(1, atomic::Ordering::AcqRel)

eden/scm/lib/dag/src/ops.rs

@@ -498,6 +498,13 @@ pub trait Open: Clone {
     fn open(&self) -> Result<Self::OpenTarget>;
 }
 
+/// Has an integer tuple version that can be used to test if the data was
+/// changed. If the first number changes, it means incompatible changes.
+/// If only the second number increases, it means append-only changes.
+pub trait IntVersion {
+    fn int_version(&self) -> (u64, u64);
+}
+
 /// Fallible clone.
 pub trait TryClone {
     fn try_clone(&self) -> Result<Self>