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frontend/node_modules/@lezer/markdown/test/test-incremental.ts

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+import {Tree, TreeFragment} from "@lezer/common"
+import ist from "ist"
+import {parser} from "../dist/index.js"
+import {compareTree} from "./compare-tree.js"
+
+let doc1 = `
+Header
+---
+One **two**
+three *four*
+five.
+
+> Start of quote
+>
+> 1. Nested list
+>
+> 2. More content
+>    inside the [list][link]
+>
+>    Continued item
+>
+>    ~~~
+>    Block of code
+>    ~~~
+>
+> 3. And so on
+
+[link]: /ref
+[another]: /one
+And a final paragraph.
+  ***  
+The end.
+`
+
+type ChangeSpec = {from: number, to?: number, insert?: string}[]
+
+class State {
+  constructor(readonly doc: string,
+              readonly tree: Tree,
+              readonly fragments: readonly TreeFragment[]) {}
+
+  static start(doc: string) {
+    let tree = parser.parse(doc)
+    return new State(doc, tree, TreeFragment.addTree(tree))
+  }
+
+  update(changes: ChangeSpec, reparse = true) {
+    let changed = [], doc = this.doc, off = 0
+    for (let {from, to = from, insert = ""} of changes) {
+      doc = doc.slice(0, from) + insert + doc.slice(to)
+      changed.push({fromA: from - off, toA: to - off, fromB: from, toB: from + insert.length})
+      off += insert.length - (to - from)
+    }
+    let fragments = TreeFragment.applyChanges(this.fragments, changed, 2)
+    if (!reparse) return new State(doc, Tree.empty, fragments)
+    let tree = parser.parse(doc, fragments)
+    return new State(doc, tree, TreeFragment.addTree(tree, fragments))
+  }
+}
+
+let _state1: State | null = null, state1 = () => _state1 || (_state1 = State.start(doc1))
+
+function overlap(a: Tree, b: Tree) {
+  let inA = new Set<Tree>(), shared = 0, sharingTo = 0
+  for (let cur = a.cursor(); cur.next();) if (cur.tree) inA.add(cur.tree)
+  for (let cur = b.cursor(); cur.next();) if (cur.tree && inA.has(cur.tree) && cur.type.is("Block") && cur.from >= sharingTo) {
+    shared += cur.to - cur.from
+    sharingTo = cur.to
+  }
+  return Math.round(shared * 100 / b.length)
+}
+
+function testChange(change: ChangeSpec, reuse = 10) {
+  let state = state1().update(change)
+  compareTree(state.tree, parser.parse(state.doc))
+  if (reuse) ist(overlap(state.tree, state1().tree), reuse, ">")
+}
+
+describe("Markdown incremental parsing", () => {
+  it("can produce the proper tree", () => {
+    // Replace 'three' with 'bears'
+    let state = state1().update([{from: 24, to: 29, insert: "bears"}])
+    compareTree(state.tree, state1().tree)
+  })
+
+  it("reuses nodes from the previous parse", () => {
+    // Replace 'three' with 'bears'
+    let state = state1().update([{from: 24, to: 29, insert: "bears"}])
+    ist(overlap(state1().tree, state.tree), 80, ">")
+  })
+
+  it("can reuse content for a change in a block context", () => {
+    // Replace 'content' with 'monkeys'
+    let state = state1().update([{from: 92, to: 99, insert: "monkeys"}])
+    compareTree(state.tree, state1().tree)
+    ist(overlap(state1().tree, state.tree), 20, ">")
+  })
+
+  it("can handle deleting a quote mark", () => testChange([{from: 82, to: 83}]))
+
+  it("can handle adding to a quoted block", () => testChange([{from: 37, insert: "> "}, {from: 45, insert: "> "}]))
+
+  it("can handle a change in a post-linkref paragraph", () => testChange([{from: 249, to: 251}]))
+
+  it("can handle a change in a paragraph-adjacent linkrefs", () => testChange([{from: 230, to: 231}]))
+
+  it("can deal with multiple changes applied separately", () => {
+    let state = state1().update([{from: 190, to: 191}], false).update([{from: 30, insert: "hi\n\nyou"}])
+    compareTree(state.tree, parser.parse(state.doc))
+    ist(overlap(state.tree, state1().tree), 20, ">")
+  })
+
+  it("works when a change happens directly after a block", () => testChange([{from: 150, to: 167}]))
+
+  it("works when a change deletes a blank line after a paragraph", () => testChange([{from: 207, to: 213}]))
+
+  it("doesn't get confused by removing paragraph-breaking markup", () => testChange([{from: 264, to: 265}]))
+
+  function r(n: number) { return Math.floor(Math.random() * n) }
+  function rStr(len: number) {
+    let result = "", chars = "\n>x-"
+    while (result.length < len) result += chars[r(chars.length)]
+    return result
+  }
+
+  it("survives random changes", () => {
+    for (let i = 0, l = doc1.length; i < 20; i++) {
+      let c = 1 + r(4), changes = []
+      for (let i = 0, rFrom = 0; i < c; i++) {
+        let rTo = rFrom + Math.floor((l - rFrom) / (c - i))
+        let from = rFrom + r(rTo - rFrom - 1), to = r(2) == 1 ? from : from + r(Math.min(rTo - from, 20))
+        let iR = r(3), insert = iR == 0 && from != to ? "" : iR == 1 ? "\n\n" : rStr(r(5) + 1)
+        changes.push({from, to, insert})
+        l += insert.length - (to - from)
+        rFrom = to + insert.length
+      }
+      testChange(changes, 0)
+    }
+  })
+
+  it("can handle large documents", () => {
+    let doc = doc1.repeat(50)
+    let state = State.start(doc)
+    let newState = state.update([{from: doc.length >> 1, insert: "a\n\nb"}])
+    ist(overlap(state.tree, newState.tree), 90, ">")
+  })
+
+  it("properly re-parses a continued indented code block", () => {
+    let state = State.start(`
+One paragraph to create a bit of string length here
+
+    Code
+    Block
+
+
+
+Another paragraph that is long enough to create a fragment
+`).update([{from: 76, insert: "    "}])
+    compareTree(state.tree, parser.parse(state.doc))
+  })
+
+  it("properly re-parses a continued list", () => {
+    let state = State.start(`
+One paragraph to create a bit of string length here
+
+ * List
+
+
+
+More content
+
+Another paragraph that is long enough to create a fragment
+`).update([{from: 65, insert: " * "}])
+    compareTree(state.tree, parser.parse(state.doc))
+  })
+
+  it("can recover from incremental parses that stop in the middle of a list", () => {
+    let doc = `
+1. I am a list item with ***some* emphasized
+   content inside** and the parser hopefully stops
+   parsing after me.
+
+2. Oh no the list continues.
+`
+    let parse = parser.startParse(doc), tree
+    parse.advance()
+    ist(parse.parsedPos, doc.length, "<")
+    parse.stopAt(parse.parsedPos)
+    while (!(tree = parse.advance())) {}
+    let state = new State(doc, tree, TreeFragment.addTree(tree)).update([])
+    ist(state.tree.topNode.lastChild!.from, 1)
+  })
+
+  it("can reuse list items", () => {
+    let start = State.start(" - List item\n".repeat(100))
+    let state = start.update([{from: 18, to: 19}])
+    ist(overlap(start.tree, state.tree), 80, ">")
+  })
+
+  it("returns a tree starting at the first range", () => {
+    let result = parser.parse("foo\n\nbar", [], [{from: 5, to: 8}])
+    ist(result.toString(), "Document(Paragraph)")
+    ist(result.length, 3)
+    ist(result.positions[0], 0)
+  })
+
+  it("Allows gaps in the input", () => {
+    let doc = `
+The first X *y* X<
+
+>X paragraph.
+
+ - And *a X<*>X list*
+`
+    let tree = parser.parse(doc, [], [{from: 0, to: 11}, {from: 12, to: 17}, {from: 23, to: 46}, {from: 51, to: 58}])
+    ist(tree.toString(),
+        "Document(Paragraph(Emphasis(EmphasisMark,EmphasisMark)),BulletList(ListItem(ListMark,Paragraph(Emphasis(EmphasisMark,EmphasisMark)))))")
+    ist(tree.length, doc.length)
+    let top = tree.topNode, first = top.firstChild!
+    ist(first.name, "Paragraph")
+    ist(first.from, 1)
+    ist(first.to, 34)
+    let last = top.lastChild!.lastChild!.lastChild!, em = last.lastChild!
+    ist(last.name, "Paragraph")
+    ist(last.from, 39)
+    ist(last.to, 57)
+    ist(em.name, "Emphasis")
+    ist(em.from, 43)
+    ist(em.to, 57)
+  })
+
+  it("can reuse nodes at the end of the document", () => {
+    let doc = `* List item
+
+~~~js
+function foo() {
+  return false
+}
+~~~
+`
+    let tree = parser.parse(doc)
+    let ins = 11
+    let doc2 = doc.slice(0, ins) + "\n* " + doc.slice(ins)
+    let fragments = TreeFragment.applyChanges(TreeFragment.addTree(tree), [{fromA: ins, toA: ins, fromB: ins, toB: ins + 3}])
+    let tree2 = parser.parse(doc2, fragments)
+    ist(tree2.topNode.lastChild!.tree, tree.topNode.lastChild!.tree)
+  })
+
+  it("places reused nodes at the right position when there are gaps before them", () => {
+    let doc = " {{}}\nb\n{{}}"
+    let ast1 = parser.parse(doc, undefined, [{from: 0, to: 1}, {from: 5, to: 8}])
+    let frag = TreeFragment.applyChanges(TreeFragment.addTree(ast1), [{fromA: 0, toA: 0, fromB: 0, toB: 1}])
+    let ast2 = parser.parse(" " + doc, frag, [{from: 0, to: 2}, {from: 6, to: 9}])
+    ist(ast2.toString(), "Document(Paragraph)")
+    let p = ast2.topNode.firstChild!
+    ist(p.from, 7)
+    ist(p.to, 8)
+  })
+})