fixes locker deadlock issue resulting from json pointer recursion being broken

patch-db/Cargo.toml

@@ -51,3 +51,4 @@ tokio = { version = "1.0.1", features = [
     "io-util",
     "macros",
 ] }
+rand = "0.8.4"

patch-db/src/locker/proptest.rs

@@ -270,6 +270,50 @@ mod tests {
         }
     }
 
+    proptest! {
+        #[test]
+        fn trie_lock_inverse_identity(lock_order in proptest::collection::vec(arb_lock_info(1, 5), 1..30)) {
+            use crate::locker::trie::LockTrie;
+            use rand::seq::SliceRandom;
+            let mut trie = LockTrie::default();
+            for i in &lock_order {
+                trie.try_lock(i).expect(&format!("try_lock failed: {}", i));
+            }
+            let mut release_order = lock_order.clone();
+            let slice: &mut [LockInfo] = &mut release_order[..];
+            slice.shuffle(&mut rand::thread_rng());
+            for i in &release_order {
+                trie.unlock(i);
+            }
+            prop_assert_eq!(trie, LockTrie::default())
+        }
+    }
+
+    proptest! {
+        #[test]
+        fn existence_ancestors_dont_block_descendent_writes(s0 in arb_handle_id(10), s1 in arb_handle_id(10), mut ptr0 in arb_json_ptr(3), ptr1 in arb_json_ptr(3)) {
+            use crate::locker::trie::LockTrie;
+            prop_assume!(s0 != s1);
+            let mut trie = LockTrie::default();
+            let li0 = LockInfo {
+                handle_id: s0,
+                ty: LockType::Exist,
+                ptr: ptr0.clone()
+            };
+            println!("{}", ptr0);
+            ptr0.append(&ptr1);
+            println!("{}", ptr0);
+            let li1 = LockInfo {
+                handle_id: s1,
+                ty: LockType::Write,
+                ptr: ptr0.clone()
+            };
+            trie.try_lock(&li0).unwrap();
+            println!("{:?}", trie);
+            trie.try_lock(&li1).expect("E locks don't prevent child locks");
+        }
+    }
+
     proptest! {
         #[test]
         fn zero_or_one_write_lock_per_traversal(x in 0..10) {

patch-db/src/locker/trie.rs

@@ -3,9 +3,10 @@ use std::collections::BTreeMap;
 use imbl::{ordset, OrdSet};
 use json_ptr::{JsonPointer, SegList};
 
-use crate::{handle::HandleId, LockType};
-
-use super::{natural::Natural, LockInfo};
+use super::natural::Natural;
+use super::LockInfo;
+use crate::handle::HandleId;
+use crate::LockType;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 enum LockState {
@@ -351,7 +352,7 @@ impl Default for LockState {
     }
 }
 
-#[derive(Debug, Default)]
+#[derive(Debug, Default, PartialEq, Eq)]
 
 pub(super) struct LockTrie {
     state: LockState,
@@ -596,9 +597,10 @@ impl LockTrie {
 
 #[cfg(test)]
 mod proptest {
-    use super::*;
     use ::proptest::prelude::*;
 
+    use super::*;
+
     fn lock_type_gen() -> BoxedStrategy<crate::LockType> {
         prop_oneof![
             Just(crate::LockType::Exist),