Fix performance of InclusiveDescendant type

index.test-d.ts

@@ -55,7 +55,7 @@ visit(implicitTree, function (node, index, parent) {
   expectAssignable<Node>(node)
   expectNotType<Node>(node)
   expectType<number | undefined>(index)
-  expectType<never>(parent)
+  expectAssignable<Parent | undefined>(parent)
 })
 
 // ## String test
@@ -126,8 +126,7 @@ visit(sampleTree, isHeading, function (node) {
 })
 // Function test (explicit assertion).
 visit(sampleTree, isHeading2, function (node) {
-  // To do: improving `InclusiveDescendant` should use `Heading & {depth: 2}`.
-  expectType<never>(node)
+  expectType<Heading & {depth: 2}>(node)
 })
 
 // ## Combined tests

lib/index.js

@@ -5,22 +5,134 @@
  * @typedef {import('unist-util-visit-parents').VisitorResult} VisitorResult
  */
 
+// To do: use types from `unist-util-visit-parents` when it’s released.
+
+/**
+ * @typedef {(
+ *   Fn extends (value: any) => value is infer Thing
+ *   ? Thing
+ *   : Fallback
+ * )} Predicate
+ *   Get the value of a type guard `Fn`.
+ * @template Fn
+ *   Value; typically function that is a type guard (such as `(x): x is Y`).
+ * @template Fallback
+ *   Value to yield if `Fn` is not a type guard.
+ */
+
 /**
  * @typedef {(
- *   Ancestor extends UnistParent
- *     ? Child extends Ancestor['children'][number]
- *       ? Ancestor
- *       : never
+ *   Check extends null | undefined // No test.
+ *   ? Value
+ *   : Value extends {type: Check} // String (type) test.
+ *   ? Value
+ *   : Value extends Check // Partial test.
+ *   ? Value
+ *   : Check extends Function // Function test.
+ *   ? Predicate<Check, Value> extends Value
+ *     ? Predicate<Check, Value>
  *     : never
- * )} ParentsOf
- *   Check if `Child` can be a child of `Ancestor`.
- *
- *   Returns the ancestor when `Child` can be a child of `Ancestor`, or returns
- *   `never`.
- * @template {UnistNode} Ancestor
- *   Node type.
+ *   : never // Some other test?
+ * )} MatchesOne
+ *   Check whether a node matches a primitive check in the type system.
+ * @template Value
+ *   Value; typically unist `Node`.
+ * @template Check
+ *   Value; typically `unist-util-is`-compatible test, but not arrays.
+ */
+
+/**
+ * @typedef {(
+ *   Check extends Array<any>
+ *   ? MatchesOne<Value, Check[keyof Check]>
+ *   : MatchesOne<Value, Check>
+ * )} Matches
+ *   Check whether a node matches a check in the type system.
+ * @template Value
+ *   Value; typically unist `Node`.
+ * @template Check
+ *   Value; typically `unist-util-is`-compatible test.
+ */
+
+/**
+ * @typedef {0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10} Uint
+ *   Number; capped reasonably.
+ */
+
+/**
+ * @typedef {I extends 0 ? 1 : I extends 1 ? 2 : I extends 2 ? 3 : I extends 3 ? 4 : I extends 4 ? 5 : I extends 5 ? 6 : I extends 6 ? 7 : I extends 7 ? 8 : I extends 8 ? 9 : 10} Increment
+ *   Increment a number in the type system.
+ * @template {Uint} [I=0]
+ *   Index.
+ */
+
+/**
+ * @typedef {(
+ *   Node extends UnistParent
+ *   ? Node extends {children: Array<infer Children>}
+ *     ? Child extends Children ? Node : never
+ *     : never
+ *   : never
+ * )} InternalParent
+ *   Collect nodes that can be parents of `Child`.
+ * @template {UnistNode} Node
+ *   All node types in a tree.
  * @template {UnistNode} Child
- *   Node type.
+ *   Node to search for.
+ */
+
+/**
+ * @typedef {InternalParent<InclusiveDescendant<Tree>, Child>} Parent
+ *   Collect nodes in `Tree` that can be parents of `Child`.
+ * @template {UnistNode} Tree
+ *   All node types in a tree.
+ * @template {UnistNode} Child
+ *   Node to search for.
+ */
+
+/**
+ * @typedef {(
+ *   Depth extends Max
+ *   ? never
+ *   :
+ *     | InternalParent<Node, Child>
+ *     | InternalAncestor<Node, InternalParent<Node, Child>, Max, Increment<Depth>>
+ * )} InternalAncestor
+ *   Collect nodes in `Tree` that can be ancestors of `Child`.
+ * @template {UnistNode} Node
+ *   All node types in a tree.
+ * @template {UnistNode} Child
+ *   Node to search for.
+ * @template {Uint} [Max=10]
+ *   Max; searches up to this depth.
+ * @template {Uint} [Depth=0]
+ *   Current depth.
+ */
+
+/**
+ * @typedef {(
+ *   Tree extends UnistParent
+ *     ? Depth extends Max
+ *       ? Tree
+ *       : Tree | InclusiveDescendant<Tree['children'][number], Max, Increment<Depth>>
+ *     : Tree
+ * )} InclusiveDescendant
+ *   Collect all (inclusive) descendants of `Tree`.
+ *
+ *   > 👉 **Note**: for performance reasons, this seems to be the fastest way to
+ *   > recurse without actually running into an infinite loop, which the
+ *   > previous version did.
+ *   >
+ *   > Practically, a max of `2` is typically enough assuming a `Root` is
+ *   > passed, but it doesn’t improve performance.
+ *   > It gets higher with `List > ListItem > Table > TableRow > TableCell`.
+ *   > Using up to `10` doesn’t hurt or help either.
+ * @template {UnistNode} Tree
+ *   Tree type.
+ * @template {Uint} [Max=10]
+ *   Max; searches up to this depth.
+ * @template {Uint} [Depth=0]
+ *   Current depth.
  */
 
 /**
@@ -45,7 +157,7 @@
  *   Found node.
  * @param {Visited extends UnistNode ? number | undefined : never} index
  *   Index of `node` in `parent`.
- * @param {Ancestor extends UnistNode ? Ancestor | undefined : never} parent
+ * @param {Ancestor extends UnistParent ? Ancestor | undefined : never} parent
  *   Parent of `node`.
  * @returns {VisitorResult}
  *   What to do next.
@@ -63,7 +175,7 @@
  */
 
 /**
- * @typedef {Visitor<Visited, ParentsOf<Ancestor, Visited>>} BuildVisitorFromMatch
+ * @typedef {Visitor<Visited, Parent<Ancestor, Visited>>} BuildVisitorFromMatch
  *   Build a typed `Visitor` function from a node and all possible parents.
  *
  *   It will infer which values are passed as `node` and which as `parent`.
@@ -76,7 +188,7 @@
 /**
  * @typedef {(
  *   BuildVisitorFromMatch<
- *     import('unist-util-visit-parents/complex-types.js').Matches<Descendant, Check>,
+ *     Matches<Descendant, Check>,
  *     Extract<Descendant, UnistParent>
  *   >
  * )} BuildVisitorFromDescendants
@@ -92,7 +204,7 @@
 /**
  * @typedef {(
  *   BuildVisitorFromDescendants<
- *     import('unist-util-visit-parents/complex-types.js').InclusiveDescendant<Tree>,
+ *     InclusiveDescendant<Tree>,
  *     Check
  *   >
  * )} BuildVisitor

package.json

@@ -92,6 +92,10 @@
   "typeCoverage": {
     "atLeast": 100,
     "detail": true,
+    "#": "needed `any`s",
+    "ignoreFiles": [
+      "lib/index.d.ts"
+    ],
     "ignoreCatch": true,
     "strict": true
   },