X-Git-Url: https://git.ladys.computer/Pisces/blobdiff_plain/aa1ae4c089cec40d79c3087ed7d6007dade77815..refs/heads/current:/function.js

diff --git a/function.js b/function.js
index d02fe6e..2f242fe 100644
--- a/function.js
+++ b/function.js
@@ -7,7 +7,23 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at <https://mozilla.org/MPL/2.0/>.
 
-import { ITERATOR, toFunctionName, toLength } from "./value.js";
+import {
+  ITERATOR,
+  toFunctionName,
+  toLength,
+  type,
+  UNDEFINED,
+} from "./value.js";
+import {
+  defineOwnDataProperty,
+  defineOwnProperties,
+  defineOwnProperty,
+  getOwnPropertyDescriptor,
+  getPrototype,
+  objectCreate,
+  setPropertyValues,
+  setPrototype,
+} from "./object.js";
 
 export const {
   /**
@@ -52,24 +68,49 @@ export const {
    * be used to override `length`, `name`, and `prototype`.
    */
   createIllegalConstructor,
+
+  /**
+   * Returns a constructor which produces a new constructor which wraps
+   * the provided constructor, but returns a proxy of the result using
+   * the provided handler.
+   *
+   * The resulting constructor inherits from, and has the same basic
+   * shape as, `Proxy`.
+   *
+   * If a base constructor is not provided, `Object` will be used.
+   *
+   * If a third argument is provided, it is used as the target for the
+   * provided constructor when it is constructed. This can be used to
+   * prevent leakage of the provided constructor to superclasses
+   * through `new.target`.
+   *
+   * The `length` of the provided function will be preserved in the new
+   * one. A fourth argument may be used to override `length` and
+   * `name`.
+   *
+   * ※ `.prototype` will be present, but undefined, on the resulting
+   * constructor. This differs from the behaviour of `Proxy`, for which
+   * `.prototype` is not present at all. It is not presently possible
+   * to create a constructor with no `.prototype` property in
+   * Ecmascript code.
+   */
+  createProxyConstructor,
 } = (() => {
   const { prototype: functionPrototype } = Function;
   const {
     bind: functionBind,
     call: functionCall,
   } = functionPrototype;
-  const { apply: reflectApply } = Reflect;
+  const objectConstructor = Object;
+  const proxyConstructor = Proxy;
   const {
-    create: objectCreate,
-    defineProperty: defineOwnProperty,
-    defineProperties: defineOwnProperties,
-    hasOwn: hasOwnProperty,
-    getPrototypeOf: getPrototype,
-    setPrototypeOf: setPrototype,
-  } = Object;
+    apply: reflectApply,
+    construct: reflectConstruct,
+  } = Reflect;
   const callBind = reflectApply(functionBind, functionCall, [
     functionBind,
   ]);
+  const { revocable } = Proxy;
   const { [ITERATOR]: arrayIterator } = Array.prototype;
   const {
     next: arrayIteratorNext,
@@ -87,8 +128,31 @@ export const {
       };
     },
   };
+  const { get: wmGet, set: wmSet } = WeakMap.prototype;
+  const wsConstructor = WeakSet;
+  const { add: wsAdd, has: wsHas } = WeakSet.prototype;
+  const proxyConstructorValuesMap = new WeakMap();
+  const registerConstructedProxy = (constructor, proxy) => {
+    const values = (() => {
+      const existing = reflectApply(wmGet, proxyConstructorValuesMap, [
+        constructor,
+      ]);
+      if (existing) {
+        return existing;
+      } else {
+        const result = new wsConstructor();
+        reflectApply(wmSet, proxyConstructorValuesMap, [
+          constructor,
+          result,
+        ]);
+        return result;
+      }
+    })();
+    reflectApply(wsAdd, values, [proxy]);
+    return proxy;
+  };
   const applyBaseFunction = ($, base, lengthDelta = 0) => {
-    if (base === undefined) {
+    if (base === UNDEFINED) {
       // No base function was provided to apply.
       return $;
     } else {
@@ -107,15 +171,18 @@ export const {
     }
   };
   const applyProperties = ($, override) => {
-    if (override === undefined) {
+    if (override === UNDEFINED) {
       // No properties were provided to apply.
       return $;
     } else {
       // Properties were provided; apply them.
       const { length, name, prototype } = override;
-      if (!hasOwnProperty($, "prototype") || prototype === undefined) {
-        // The provided function has no `.prototype` or no prototype
-        // value was provided.
+      if (
+        prototype === UNDEFINED ||
+        !getOwnPropertyDescriptor($, "prototype")?.writable
+      ) {
+        // The provided function has no `.prototype`, its prototype is
+        // not writable, or no prototype value was provided.
         //
         // Do not modify the prototype property of the provided
         // function.
@@ -126,17 +193,27 @@ export const {
         //
         // Change the prototype property of the provided function to
         // match.
-        defineOwnProperty($, "prototype", { value: prototype });
+        defineOwnProperty(
+          $,
+          "prototype",
+          defineOwnDataProperty(
+            objectCreate(null),
+            "value",
+            prototype,
+          ),
+        );
       }
       return defineOwnProperties($, {
-        length: {
-          value: toLength(length === undefined ? $.length : length),
-        },
-        name: {
-          value: toFunctionName(
-            name === undefined ? $.name ?? "" : name,
-          ),
-        },
+        length: defineOwnDataProperty(
+          objectCreate(null),
+          "value",
+          toLength(length === UNDEFINED ? $.length : length),
+        ),
+        name: defineOwnDataProperty(
+          objectCreate(null),
+          "value",
+          toFunctionName(name === UNDEFINED ? $.name ?? "" : name),
+        ),
       });
     }
   };
@@ -146,26 +223,28 @@ export const {
       callBind(
         $,
         boundThis,
-        ...objectCreate(
-          argumentIterablePrototype,
-          { args: { value: boundArgs } },
+        ...defineOwnDataProperty(
+          objectCreate(argumentIterablePrototype),
+          "args",
+          boundArgs,
         ),
       ),
-    createArrowFunction: ($, propertyOverride = undefined) =>
+    createArrowFunction: ($, propertyOverride = UNDEFINED) =>
       applyProperties(
         applyBaseFunction(
-          (...$s) => reflectApply($, undefined, $s),
+          (...$s) => reflectApply($, UNDEFINED, $s),
           $,
         ),
         propertyOverride,
       ),
-    createCallableFunction: ($, propertyOverride = undefined) =>
+    createCallableFunction: ($, propertyOverride = UNDEFINED) =>
       applyProperties(
         applyBaseFunction(
           (...$s) => {
-            const iterator = objectCreate(
-              argumentIterablePrototype,
-              { args: { value: $s } },
+            const iterator = defineOwnDataProperty(
+              objectCreate(argumentIterablePrototype),
+              "args",
+              $s,
             )[ITERATOR]();
             const { value: thisValue } = iterator.next();
             return reflectApply($, thisValue, [...iterator]);
@@ -175,7 +254,7 @@ export const {
         ),
         propertyOverride,
       ),
-    createIllegalConstructor: ($, propertyOverride = undefined) =>
+    createIllegalConstructor: ($, propertyOverride = UNDEFINED) =>
       defineOwnProperty(
         applyProperties(
           applyBaseFunction(
@@ -189,6 +268,148 @@ export const {
         "prototype",
         { writable: false },
       ),
+    createProxyConstructor: (
+      handler,
+      $,
+      newTarget = UNDEFINED,
+      propertyOverride = UNDEFINED,
+    ) => {
+      const constructor = $ === UNDEFINED
+        ? function ($) {
+          return new objectConstructor($);
+        }
+        : $;
+      const target = newTarget === UNDEFINED ? constructor : newTarget;
+      const len = toLength(constructor.length);
+      if (!(type(handler) === "object")) {
+        // The provided handler is not an object; this is an error.
+        throw new TypeError(
+          `Piscēs: Proxy handler must be an object, but got: ${handler}.`,
+        );
+      } else if (!isConstructor(constructor)) {
+        // The provided constructor is not a constructor; this is an
+        // error.
+        throw new TypeError(
+          "Piscēs: Cannot create proxy constructor from nonconstructible value.",
+        );
+      } else if (!isConstructor(target)) {
+        // The provided new target is not a constructor; this is an
+        // error.
+        throw new TypeError(
+          "Piscēs: New target must be a constructor.",
+        );
+      } else {
+        // The arguments are acceptable.
+        const C = applyProperties(
+          defineOwnProperties(
+            setPrototype(
+              function (...$s) {
+                if (new.target === UNDEFINED) {
+                  // The constructor was not called with new; this is an
+                  // error.
+                  throw new TypeError(
+                    `Piscēs: ${
+                      C.name ?? "Proxy"
+                    } must be called with new.`,
+                  );
+                } else {
+                  // The constructor was called with new; return the
+                  // appropriate proxy.
+                  const O = reflectConstruct(
+                    constructor,
+                    $s,
+                    target,
+                  );
+                  const proxy = new proxyConstructor(O, handler);
+                  return registerConstructedProxy(C, proxy);
+                }
+              },
+              proxyConstructor,
+            ),
+            {
+              length: defineOwnDataProperty(
+                objectCreate(null),
+                "value",
+                len,
+              ),
+              name: defineOwnDataProperty(
+                objectCreate(null),
+                "value",
+                `${toFunctionName(constructor.name ?? "")}Proxy`,
+              ),
+              prototype: setPropertyValues(objectCreate(null), {
+                configurable: false,
+                enumerable: false,
+                value: UNDEFINED,
+                writable: false,
+              }),
+            },
+          ),
+          propertyOverride,
+        );
+        const { name } = C;
+        return defineOwnProperties(C, {
+          revocable: setPropertyValues(objectCreate(null), {
+            configurable: true,
+            enumerable: false,
+            value: defineOwnProperties(
+              (...$s) => {
+                const O = reflectConstruct(
+                  constructor,
+                  $s,
+                  target,
+                );
+                const proxy = revocable(O, handler);
+                return registerConstructedProxy(C, proxy);
+              },
+              {
+                length: defineOwnDataProperty(
+                  objectCreate(null),
+                  "value",
+                  len,
+                ),
+                name: defineOwnDataProperty(
+                  objectCreate(null),
+                  "value",
+                  "revocable",
+                ),
+              },
+            ),
+            writable: true,
+          }),
+          [`is${name}`]: setPropertyValues(objectCreate(null), {
+            configurable: true,
+            enumerable: false,
+            value: defineOwnProperty(
+              ($) => {
+                const values = reflectApply(
+                  wmGet,
+                  proxyConstructorValuesMap,
+                  [C],
+                );
+                if (values === UNDEFINED) {
+                  // No values have been registered for the current
+                  // constructor.
+                  return false;
+                } else {
+                  // One or more values has been registered for the
+                  // current constructor; return whether the provided
+                  // argument is one.
+                  return reflectApply(wsHas, values, [$]);
+                }
+              },
+              "name",
+              defineOwnDataProperty(
+                objectCreate(null),
+                "value",
+                `is${name}`,
+              ),
+            ),
+            writable: true,
+          }),
+        });
+      }
+    },
   };
 })();
 
@@ -262,6 +483,13 @@ export const isConstructor = ($) =>
     construct(function () {}, [], $)
   );
 
+/**
+ * Calls the provided callback with the provided argument if the
+ * provided argument is not nullish; otherwise, returns the provided
+ * argument unmodified.
+ */
+export const maybe = ($, callback) => $ == null ? $ : callback($);
+
 /**
  * Returns whether the provided object inherits from the prototype of
  * the provided function.