feat(Lists): add auto merging of adjacent list of same type (#241)

src/extensions/markdown/Lists/index.ts

@@ -9,6 +9,7 @@ import {actions} from './actions';
 import {joinPrevList, liftIfCursorIsAtBeginningOfItem, toList} from './commands';
 import {ListAction} from './const';
 import {ListsInputRulesExtension, ListsInputRulesOptions} from './inputrules';
+import {mergeListsPlugin} from './plugins/MergeListsPlugin';
 
 export {ListNode, blType, liType, olType} from './ListsSpecs';
 
@@ -48,6 +49,8 @@ export const Lists: ExtensionAuto<ListsOptions> = (builder, opts) => {
 
     builder.use(ListsInputRulesExtension, {bulletListInputRule: opts?.ulInputRules});
 
+    builder.addPlugin(mergeListsPlugin);
+
     builder
         .addAction(ListAction.ToBulletList, actions.toBulletList)
         .addAction(ListAction.ToOrderedList, actions.toOrderedList)

src/extensions/markdown/Lists/plugins/MergeListsPlugin.ts

@@ -0,0 +1,41 @@
+import {Plugin, Transaction} from 'prosemirror-state';
+import {findChildren, hasParentNode} from 'prosemirror-utils';
+
+import {isListNode} from '../utils';
+
+export const mergeListsPlugin = () =>
+    new Plugin({
+        appendTransaction(trs, oldState, newState) {
+            const docChanged = trs.some((tr) => tr.docChanged);
+            if (!docChanged) return null;
+
+            const hasParentList =
+                hasParentNode(isListNode)(newState.selection) ||
+                hasParentNode(isListNode)(oldState.selection);
+            if (!hasParentList) return null;
+
+            const {tr} = newState;
+            const listNodes = findChildren(tr.doc, isListNode, true);
+
+            mergeAdjacentNodesWithSameType(tr, listNodes);
+
+            return tr.docChanged ? tr : null;
+        },
+    });
+
+function mergeAdjacentNodesWithSameType(
+    tr: Transaction,
+    nodes: ReturnType<typeof findChildren>,
+): void {
+    for (let i = 0; i < nodes.length - 1; i++) {
+        const current = nodes[i];
+        const next = nodes[i + 1];
+
+        if (
+            current.node.type === next.node.type &&
+            current.pos + current.node.nodeSize === next.pos
+        ) {
+            tr.join(next.pos);
+        }
+    }
+}