Improve DescriptorRegistry (#77)

README.md

@@ -34,7 +34,7 @@ for the [generated code](docs/generated_code.md), and the documentation for the
 
 ### How does this compare to protoc's JavaScript generator?
 
-[`js_generator.cc`](https://github.com/protocolbuffers/protobuf/blob/main/src/google/protobuf/compiler/js/js_generator.cc)
+[`js_generator.cc`](https://github.com/protocolbuffers/protobuf-javascript/blob/main/generator/js_generator.cc)
 is rarely updated, and has fallen behind the quickly moving world of JavaScript.
 
 For example:

docs/generated_code.md

@@ -219,8 +219,9 @@ Note that all map fields will have an empty object as a default value.
 
 While it is not a perfectly clear-cut case, we chose to represent map fields
 as plain objects instead of [ECMAScript map objects](https://tc39.es/ecma262/multipage/keyed-collections.html#sec-map-objects).
-While `Map` has some benefits like better behavior around keys, they don't
-have a literal representation and do not support the spread operator.
+While `Map` has better behavior around keys, they do not have a literal 
+representation, do not support the spread operator and type narrowing in 
+TypeScript.
 
 
 ### Oneof groups

docs/runtime_api.md

@@ -275,10 +275,8 @@ buf generate --output image.bin
 ```
 
 ```typescript
-const fds = FileDescriptorSet.fromBinary(readFileSync("image.bin"));
-const dr = new DescriptorRegistry();
-for (const fd of fds.file) {
-  dr.add(fd);
-}
-const Example = dr.findMessage("doc.Example");
+const registry = new DescriptorRegistry.fromFileDescriptorSet(
+  readFileSync("image.bin")
+);
+const Example = registry.findMessage("doc.Example");
 ```

packages/protobuf-test/src/descriptor-registry.test.ts

@@ -21,7 +21,8 @@ import {
 import { TestAllTypes } from "./gen/ts/google/protobuf/unittest_proto3_pb.js";
 import { assertMessageTypeEquals } from "./helpers.js";
 
-const fds = FileDescriptorSet.fromBinary(readFileSync("./descriptorset.bin"));
+const fdsBytes = readFileSync("./descriptorset.bin");
+const fds = FileDescriptorSet.fromBinary(fdsBytes);
 
 describe("DescriptorSet", () => {
   test("add() does not crash", () => {
@@ -39,14 +40,22 @@ describe("DescriptorRegistry", () => {
     expect(dr.findMessage("foo.Foo")).toBeUndefined();
     expect(dr.findEnum("foo.Foo")).toBeUndefined();
   });
-  test("dynamic type equals generated type", () => {
-    const dr = new DescriptorRegistry();
-    dr.add(...fds.file);
-    const messageTypeDyn = dr.findMessage(TestAllTypes.typeName);
-    expect(messageTypeDyn).toBeDefined();
-    if (!messageTypeDyn) {
-      return;
+  test("fromDescriptorSet with instance", () => {
+    const dr = DescriptorRegistry.fromFileDescriptorSet(fds);
+    expect(dr.findEnum("foo.Foo")).toBeUndefined();
+    const mt = dr.findMessage(TestAllTypes.typeName);
+    expect(mt).toBeDefined();
+    if (mt) {
+      assertMessageTypeEquals(mt, TestAllTypes);
+    }
+  });
+  test("fromDescriptorSet with bytes", () => {
+    const dr = DescriptorRegistry.fromFileDescriptorSet(fdsBytes);
+    expect(dr.findEnum("foo.Foo")).toBeUndefined();
+    const mt = dr.findMessage(TestAllTypes.typeName);
+    expect(mt).toBeDefined();
+    if (mt) {
+      assertMessageTypeEquals(mt, TestAllTypes);
     }
-    assertMessageTypeEquals(messageTypeDyn, TestAllTypes);
   });
 });

packages/protobuf/src/descriptor-registry.ts

@@ -52,6 +52,8 @@ import {
   UInt32Value,
   UInt64Value,
 } from "./google/protobuf/wrappers_pb.js";
+import { FileDescriptorSet } from "./google/protobuf/descriptor_pb.js";
+import type { PartialMessage } from "./message.js";
 
 // well-known message types with specialized JSON representation
 const wkMessages = [
@@ -106,6 +108,25 @@ export class DescriptorRegistry
     }
   }
 
+  /**
+   * Conveniently create a DescriptorRegistry from a FileDescriptorSet
+   * instance or a FileDescriptorSet in binary format.
+   */
+  static fromFileDescriptorSet(
+    bytesOrSet:
+      | Uint8Array
+      | FileDescriptorSet
+      | PartialMessage<FileDescriptorSet>
+  ): DescriptorRegistry {
+    const set =
+      bytesOrSet instanceof Uint8Array
+        ? FileDescriptorSet.fromBinary(bytesOrSet)
+        : new FileDescriptorSet(bytesOrSet);
+    const dr = new DescriptorRegistry();
+    dr.add(...set.file);
+    return dr;
+  }
+
   /**
    * May raise an error on invalid descriptors.
    */

private/protoplugin/protoplugin.go

@@ -561,7 +561,7 @@ type Message struct {
 	File              *File
 	Proto             *descriptorpb.DescriptorProto
 	TypeName          string  // fully qualified name, for example `foo.MyMessage`
-	Symbol            *Symbol // importable of this message in ECMAScript
+	Symbol            *Symbol // importable name of this message in ECMAScript
 	Members           []*Member
 	Fields            []*Field
 	Oneofs            []*Oneof // excluding synthetic oneofs for proto3 optional