Fix remote change handling

src/PatchSemaphore.ts

@@ -1,4 +1,4 @@
-import { next as automerge } from "@automerge/automerge"
+import { next as automerge, equals } from "@automerge/automerge"
 import { DocHandle } from "@automerge/automerge-repo"
 import { EditorView } from "@codemirror/view"
 import codeMirrorToAm from "./codeMirrorToAm"
@@ -70,7 +70,7 @@ export class PatchSemaphore {
 
       // now get the diff between the updated state of the document and the heads
       // and apply that to the codemirror doc
-      const diff = automerge.diff(handle.docSync(), oldHeads, newHeads)
+      const diff = automerge.equals(oldHeads, newHeads) ? [] : automerge.diff(handle.docSync(), oldHeads, newHeads)
       amToCodemirror(view, selection, path, diff)
 
       view.dispatch({

src/amToCodemirror.ts

@@ -3,9 +3,10 @@ import {
   InsertPatch,
   Patch,
   Prop,
+  PutPatch,
   SpliceTextPatch,
 } from "@automerge/automerge"
-import { ChangeSet, ChangeSpec, EditorSelection } from "@codemirror/state"
+import { ChangeSet, ChangeSpec, EditorSelection, EditorState } from "@codemirror/state"
 import { EditorView } from "@codemirror/view"
 import { reconcileAnnotationType } from "./plugin"
 
@@ -16,7 +17,7 @@ export default function (
   patches: Patch[]
 ) {
   for (const patch of patches) {
-    const changeSpec = handlePatch(patch, target)
+    const changeSpec = handlePatch(patch, target, view.state)
     if (changeSpec != null) {
       const changeSet = ChangeSet.of(changeSpec, view.state.doc.length, "\n")
       selection = selection.map(changeSet, 1)
@@ -32,13 +33,15 @@ export default function (
   })
 }
 
-function handlePatch(patch: Patch, target: Prop[]): ChangeSpec | null {
+function handlePatch(patch: Patch, target: Prop[], state: EditorState): ChangeSpec | null {
   if (patch.action === "insert") {
     return handleInsert(target, patch)
   } else if (patch.action === "splice") {
     return handleSplice(target, patch)
   } else if (patch.action === "del") {
     return handleDel(target, patch)
+  } else if(patch.action === "put") {
+    return handlePut(target, patch, state)
   } else {
     return null
   }
@@ -73,6 +76,18 @@ function handleDel(target: Prop[], patch: DelPatch): Array<ChangeSpec> {
   return [{ from: index, to: index + length }]
 }
 
+function handlePut(target: Prop[], patch: PutPatch, state: EditorState): Array<ChangeSpec> {
+  const index = charPath(target, [...patch.path, 0]);
+  if (index == null) {
+      return [];
+  }
+  const length = state.doc.length;
+  if(typeof patch.value !== "string") {
+    return [] // TODO(dmaretskyi): How to handle non string values?
+  }
+  return [{ from: 0, to: length, insert: patch.value as any }];
+}
+
 // If the path of the patch is of the form [path, <index>] then we know this is
 // a path to a character within the sequence given by path
 function charPath(textPath: Prop[], candidatePath: Prop[]): number | null {

src/codeMirrorToAm.ts

@@ -16,6 +16,21 @@ export default function (
 ): Heads | undefined {
   const { lastHeads, path } = state.field(field)
 
+  // We don't want to call `automerge.updateAt` if there are no changes.
+  // Otherwise later on `automerge.diff` will return empty patches that result in a no-op but still mess up the selection.
+  let hasChanges = false;
+  for (const tr of transactions) {
+    if (tr.changes.length) {
+      tr.changes.iterChanges(() => {
+        hasChanges = true;
+      });
+    }
+  }
+
+  if(!hasChanges) {
+    return undefined;
+  }
+
   const newHeads = update(lastHeads, (doc: am.Doc<unknown>) => {
     for (const tr of transactions) {
       tr.changes.iterChanges(