add folding

Author: xiaoxinghu

packages/codemirror-lang/index.js

@@ -1,19 +1,89 @@
+/** @typedef {import('@lezer/common').SyntaxNode} SyntaxNode */
+
 import {
+  defineLanguageFacet,
+  foldNodeProp,
+  foldService,
   Language,
   LanguageSupport,
-  defineLanguageFacet,
+  syntaxTree,
 } from '@codemirror/language'
-import { parser, tags as t } from '@orgajs/lezer'
+import { NodeProp } from '@lezer/common'
+import { parser as baseParser, tags as t } from '@orgajs/lezer'
 
 export const tags = t
 
 const data = defineLanguageFacet({})
 
+// --- folding ---
+/** @type {NodeProp<number>} */
+const headlineProp = new NodeProp()
+
+/**
+ * @param {import('@lezer/common').NodeType} type
+ */
+function isHeadline(type) {
+  let match = /^headline(\d)$/.exec(type.name)
+  return match ? +match[1] : undefined
+}
+
+/**
+ * @param {SyntaxNode} headerNode
+ * @param {number} level
+ */
+function findSectionEnd(headerNode, level) {
+  let last = headerNode
+  for (;;) {
+    let next = last.nextSibling
+    if (!next) break
+    const headline = isHeadline(next.type)
+    if (headline != null) {
+      if (headline <= level) {
+        return next.from - 1 // escape the newline. TODO: is this safe?
+      }
+    }
+    last = next
+  }
+  return last.to
+}
+
+const headerIndent = foldService.of((state, start, end) => {
+  for (
+    let /** @type {SyntaxNode | null} */ node = syntaxTree(state).resolveInner(
+        end,
+        -1
+      );
+    node;
+    node = node.parent
+  ) {
+    if (node.from < start) break
+    let headline = node.type.prop(headlineProp)
+    if (headline == null) continue
+    let upto = findSectionEnd(node, headline)
+    if (upto > end) return { from: end, to: upto }
+  }
+  return null
+})
+
+const parser = baseParser.configure({
+  props: [
+    foldNodeProp.add((type) => {
+      const m = isHeadline(type)
+      if (!m) return undefined
+      return (tree, state) => ({
+        from: state.doc.lineAt(tree.from).to,
+        to: state.doc.lineAt(tree.from).to,
+      })
+    }),
+    headlineProp.add(isHeadline),
+  ],
+})
+
 /**
  * @param {any} parser
  */
 function mkLang(parser) {
-  return new Language(data, parser, [], 'org')
+  return new Language(data, parser, [headerIndent], 'org')
 }
 
 export function org() {

packages/codemirror-lang/package.json

@@ -30,5 +30,8 @@
   "dependencies": {
     "@codemirror/language": "^6.9.0",
     "@orgajs/lezer": "workspace:^"
+  },
+  "devDependencies": {
+    "@lezer/common": "^1.1.0"
   }
 }