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node_modules/regenerator-transform/src/meta.js

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+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import assert from "assert";
+import { getTypes } from "./util.js";
+
+const mMap = new WeakMap();
+function m(node) {
+  if (!mMap.has(node)) {
+    mMap.set(node, {});
+  }
+  return mMap.get(node);
+}
+
+const hasOwn = Object.prototype.hasOwnProperty;
+
+function makePredicate(propertyName, knownTypes) {
+  function onlyChildren(node) {
+    const t = getTypes();
+    t.assertNode(node);
+
+    // Assume no side effects until we find out otherwise.
+    let result = false;
+
+    function check(child) {
+      if (result) {
+        // Do nothing.
+      } else if (Array.isArray(child)) {
+        child.some(check);
+      } else if (t.isNode(child)) {
+        assert.strictEqual(result, false);
+        result = predicate(child);
+      }
+      return result;
+    }
+
+    let keys = t.VISITOR_KEYS[node.type];
+    if (keys) {
+      for (let i = 0; i < keys.length; i++) {
+        let key = keys[i];
+        let child = node[key];
+        check(child);
+      }
+    }
+
+    return result;
+  }
+
+  function predicate(node) {
+    getTypes().assertNode(node);
+
+    let meta = m(node);
+    if (hasOwn.call(meta, propertyName))
+      return meta[propertyName];
+
+    // Certain types are "opaque," which means they have no side
+    // effects or leaps and we don't care about their subexpressions.
+    if (hasOwn.call(opaqueTypes, node.type))
+      return meta[propertyName] = false;
+
+    if (hasOwn.call(knownTypes, node.type))
+      return meta[propertyName] = true;
+
+    return meta[propertyName] = onlyChildren(node);
+  }
+
+  predicate.onlyChildren = onlyChildren;
+
+  return predicate;
+}
+
+let opaqueTypes = {
+  FunctionExpression: true,
+  ArrowFunctionExpression: true
+};
+
+// These types potentially have side effects regardless of what side
+// effects their subexpressions have.
+let sideEffectTypes = {
+  CallExpression: true, // Anything could happen!
+  ForInStatement: true, // Modifies the key variable.
+  UnaryExpression: true, // Think delete.
+  BinaryExpression: true, // Might invoke .toString() or .valueOf().
+  AssignmentExpression: true, // Side-effecting by definition.
+  UpdateExpression: true, // Updates are essentially assignments.
+  NewExpression: true // Similar to CallExpression.
+};
+
+// These types are the direct cause of all leaps in control flow.
+let leapTypes = {
+  YieldExpression: true,
+  BreakStatement: true,
+  ContinueStatement: true,
+  ReturnStatement: true,
+  ThrowStatement: true
+};
+
+// All leap types are also side effect types.
+for (let type in leapTypes) {
+  if (hasOwn.call(leapTypes, type)) {
+    sideEffectTypes[type] = leapTypes[type];
+  }
+}
+
+exports.hasSideEffects = makePredicate("hasSideEffects", sideEffectTypes);
+exports.containsLeap = makePredicate("containsLeap", leapTypes);