feat: init

node_modules/oxc-parser/src-js/raw-transfer/visitor.js

@@ -0,0 +1,127 @@
+import {
+  LEAF_NODE_TYPES_COUNT,
+  NODE_TYPE_IDS_MAP,
+  NODE_TYPES_COUNT,
+} from "../generated/lazy/type_ids.js";
+
+// Getter for private `#visitorsArr` property of `Visitor` class. Initialized in class body below.
+let getVisitorsArrTemp;
+
+/**
+ * Visitor class, used to visit an AST.
+ */
+export class Visitor {
+  #visitorsArr;
+
+  /**
+   * Create `Visitor`.
+   *
+   * Provide an object where keys are names of AST nodes you want to visit,
+   * and values are visitor functions which receive AST node objects of that type.
+   *
+   * Keys can also be postfixed with `:exit` to visit when exiting the node, rather than entering.
+   *
+   * ```js
+   * const visitor = new Visitor({
+   *     BinaryExpression(binExpr) {
+   *         // Do stuff when entering a `BinaryExpression`
+   *     },
+   *     'BinaryExpression:exit'(binExpr) {
+   *         // Do stuff when exiting a `BinaryExpression`
+   *     },
+   * });
+   * ```
+   *
+   * @class
+   * @param {Object} visitor - Object defining visit functions for AST nodes
+   * @returns {Visitor}
+   */
+  constructor(visitor) {
+    this.#visitorsArr = createVisitorsArr(visitor);
+  }
+
+  static {
+    getVisitorsArrTemp = (visitor) => visitor.#visitorsArr;
+  }
+}
+
+export const getVisitorsArr = getVisitorsArrTemp;
+
+/**
+ * Create array of visitors, keyed by node type ID.
+ *
+ * Each element of array is one of:
+ *
+ * * No visitor for this type = `null`.
+ * * Visitor for leaf node = visit function.
+ * * Visitor for non-leaf node = object of form `{ enter, exit }`,
+ *   where each property is either a visitor function or `null`.
+ *
+ * @param {Object} visitor - Visitors object from user
+ * @returns {Array<Object|Function|null>} - Array of visitors
+ */
+function createVisitorsArr(visitor) {
+  if (visitor === null || typeof visitor !== "object") {
+    throw new Error("`visitor` must be an object");
+  }
+
+  // Create empty visitors array
+  const visitorsArr = [];
+  for (let i = NODE_TYPES_COUNT; i !== 0; i--) {
+    visitorsArr.push(null);
+  }
+
+  // Populate visitors array from provided object
+  for (let name of Object.keys(visitor)) {
+    const visitFn = visitor[name];
+    if (typeof visitFn !== "function") {
+      throw new Error(`'${name}' property of \`visitor\` object is not a function`);
+    }
+
+    const isExit = name.endsWith(":exit");
+    if (isExit) name = name.slice(0, -5);
+
+    const typeId = NODE_TYPE_IDS_MAP.get(name);
+    if (typeId === void 0) throw new Error(`Unknown node type '${name}' in \`visitor\` object`);
+
+    if (typeId < LEAF_NODE_TYPES_COUNT) {
+      // Leaf node. Store just 1 function.
+      const existingVisitFn = visitorsArr[typeId];
+      if (existingVisitFn === null) {
+        visitorsArr[typeId] = visitFn;
+      } else if (isExit) {
+        visitorsArr[typeId] = combineVisitFunctions(existingVisitFn, visitFn);
+      } else {
+        visitorsArr[typeId] = combineVisitFunctions(visitFn, existingVisitFn);
+      }
+      continue;
+    }
+
+    let enterExit = visitorsArr[typeId];
+    if (enterExit === null) {
+      enterExit = visitorsArr[typeId] = { enter: null, exit: null };
+    }
+
+    if (isExit) {
+      enterExit.exit = visitFn;
+    } else {
+      enterExit.enter = visitFn;
+    }
+  }
+
+  return visitorsArr;
+}
+
+/**
+ * Combine 2 visitor functions into 1.
+ *
+ * @param {function} visit1 - 1st visitor function
+ * @param {function} visit2 - 2nd visitor function
+ * @returns {function} - Combined visitor function
+ */
+function combineVisitFunctions(visit1, visit2) {
+  return function (node) {
+    visit1(node);
+    visit2(node);
+  };
+}