fix(loro.js): record absent-key map deletes and zero counter increments like loro-crdt

.changeset/loro-js-local-op-parity.md

@@ -0,0 +1,8 @@
+---
+"loro.js": patch
+---
+
+`loro.js` now records the same local ops as `loro-crdt` for these API calls, so a document edited through either package gets the same op IDs and the same concurrent outcomes:
+
+- `LoroMap.delete(key)` records a delete even when the key is absent. Like in Rust, that delete can win against a concurrent `set` of the same key.
+- `LoroCounter.increment(0)` records an increment, and attaching a detached counter records an increment by its value, even 0.

loro-js/src/runtime/document.ts

@@ -4026,8 +4026,8 @@ export class LoroDoc<T extends Record<string, Container> = Record<string, Contai
   }
 
   _mapDelete(container: LoroMap, key: string): void {
-    const current = container._entries.get(key);
-    if (current === undefined || current.deleted) return;
+    // Rust records a delete even when the key is absent: it can still win
+    // against a concurrent set.
     this.#appendAndApply(container, { type: "map-delete", key }, 1);
   }
 
@@ -4180,7 +4180,6 @@ export class LoroDoc<T extends Record<string, Container> = Record<string, Contai
   }
 
   _counterIncrement(container: LoroCounter, value: number): void {
-    if (value === 0) return;
     this.#appendAndApply(
       container,
       { type: "future", property: 0, value: { type: "double", value } },
@@ -10223,7 +10222,8 @@ function restoreBlueprint(container: Container, blueprint: ContainerBlueprint):
   } else if (container instanceof LoroText) {
     container.applyDelta(blueprint.value as never);
   } else if (container instanceof LoroCounter) {
-    if ((blueprint.value as number) !== 0) container.increment(blueprint.value as number);
+    // Rust's CounterHandler::attach increments by the detached value, even 0.
+    container.increment(blueprint.value as number);
   } else if (container instanceof LoroList) {
     for (const value of blueprint.value as unknown[]) {
       if (isContainer(value)) container.pushContainer(value);

loro-js/tests/runtime.test.ts

@@ -1726,22 +1726,42 @@ describe("loro-wasm-compatible runtime", () => {
     expect(() => root.ensureMergeableMap("regular")).toThrow(/non-mergeable value/u);
   });
 
-  test("does not record semantic no-op edits", () => {
+  // loro-crdt skips setting a map key to its current value, but records a
+  // delete of an absent key and a zero counter increment. Matching it keeps op
+  // IDs and concurrent outcomes the same for the same API calls.
+  test("records the same local ops as loro-crdt for no-op-looking edits", () => {
     const doc = new LoroDoc();
     const map = doc.getMap("map");
     map.set("value", { nested: [1, true, null] });
-    const movable = doc.getMovableList("movable");
-    movable.push("same");
-    doc.commit();
-    const opCount = doc.opCount();
-
-    map.set("value", { nested: [1, true, null] });
-    map.delete("missing");
-    movable.set(0, "same");
-    doc.getCounter("counter").increment(0);
     doc.commit();
+    const count = (edit: () => void): number => {
+      const before = doc.opCount();
+      edit();
+      doc.commit();
+      return doc.opCount() - before;
+    };
 
-    expect(doc.opCount()).toBe(opCount);
+    expect(count(() => map.set("value", { nested: [1, true, null] }))).toBe(0);
+    expect(count(() => map.delete("missing"))).toBe(1);
+    expect(count(() => doc.getCounter("counter").increment(0))).toBe(1);
+    // Attaching a detached counter increments it by its value, even 0.
+    expect(count(() => map.setContainer("child", new LoroCounter()))).toBe(2);
+  });
+
+  test("lets a delete of an absent map key win against a concurrent set", () => {
+    const a = new LoroDoc();
+    a.setPeerId(1);
+    const b = new LoroDoc();
+    b.setPeerId(2);
+    a.getMap("map").set("key", 1);
+    a.commit();
+    b.getMap("map").delete("key");
+    b.commit();
+    a.import(b.export({ mode: "update" }));
+    b.import(a.export({ mode: "update" }));
+    // Same lamport; the larger peer's delete wins, as in loro-crdt.
+    expect(a.toJSON()).toEqual({ map: {} });
+    expect(b.toJSON()).toEqual({ map: {} });
   });
 
   test("resurfaces preserved state and switches mergeable kinds", () => {