Make initial ModuleInfo.meta mutable and maintain object identity

docs/05-plugin-development.md

@@ -1055,7 +1055,7 @@ Note the convention that custom options should be added using a property corresp
 
 #### Custom module meta-data
 
-Plugins can annotate modules with custom meta-data which can be accessed by themselves and other plugins via the [`resolveId`](guide/en/#resolveid), [`load`](guide/en/#load), and [`transform`](guide/en/#transform) hooks. This meta-data should always be JSON.stringifyable and will be persisted in the cache e.g. in watch mode.
+Plugins can annotate modules with custom meta-data which can be set by themselves and other plugins via the [`resolveId`](guide/en/#resolveid), [`load`](guide/en/#load), and [`transform`](guide/en/#transform) hooks and accessed via [`this.getModuleInfo`](guide/en/#thisgetmoduleinfo), [`this.load`](guide/en/#thisload) and the [`moduleParsed`](guide/en/#moduleparsed) hook. This meta-data should always be JSON.stringifyable and will be persisted in the cache e.g. in watch mode.
 
 ```js
 function annotatingPlugin() {
@@ -1087,6 +1087,26 @@ Note the convention that plugins that add or modify data should use a property c
 
 If several plugins add meta-data or meta-data is added in different hooks, then these `meta` objects will be merged shallowly. That means if plugin `first` adds `{meta: {first: {resolved: "first"}}}` in the resolveId hook and `{meta: {first: {loaded: "first"}}}` in the load hook while plugin `second` adds `{meta: {second: {transformed: "second"}}}` in the `transform` hook, then the resulting `meta` object will be `{first: {loaded: "first"}, second: {transformed: "second"}}`. Here the result of the `resolveId` hook will be overwritten by the result of the `load` hook as the plugin was both storing them under its `first` top-level property. The `transform` data of the other plugin on the other hand will be placed next to it.
 
+The `meta` object of a module is created as soon as Rollup starts loading a module and is updated for each lifecycle hook of the module. If you store a reference to this object, you can also update it manually. To access the meta object of a module that has not been loaded yet, you can trigger its creation and loading the module via [`this.load`](guide/en/#thisload):
+
+```js
+function plugin() {
+  return {
+    name: 'test',
+    buildStart() {
+      // trigger loading a module. We could also pass an initial "meta" object
+      // here, but it would be ignored if the module was already loaded via
+      // other means
+      this.load({ id: 'my-id' });
+      // the module info is now available, we do not need to await this.load
+      const meta = this.getModuleInfo('my-id').meta;
+      // we can also modify meta manually now
+      meta.test = { some: 'data' };
+    }
+  };
+}
+```
+
 #### Direct plugin communication
 
 For any other kind of inter-plugin communication, we recommend the pattern below. Note that `api` will never conflict with any upcoming plugin hooks.

src/Module.ts

@@ -840,7 +840,7 @@ export default class Module {
 			this.info.syntheticNamedExports = syntheticNamedExports;
 		}
 		if (meta != null) {
-			this.info.meta = { ...this.info.meta, ...meta };
+			Object.assign(this.info.meta, meta);
 		}
 	}
 

src/ModuleLoader.ts

@@ -204,7 +204,7 @@ export class ModuleLoader {
 		return {
 			external,
 			id: resolvedId.id,
-			meta: resolvedId.meta || EMPTY_OBJECT,
+			meta: resolvedId.meta || {},
 			moduleSideEffects:
 				resolvedId.moduleSideEffects ?? this.hasModuleSideEffects(resolvedId.id, !!external),
 			syntheticNamedExports: resolvedId.syntheticNamedExports ?? false
@@ -555,7 +555,7 @@ export class ModuleLoader {
 			return {
 				external: true,
 				id: source,
-				meta: EMPTY_OBJECT,
+				meta: {},
 				moduleSideEffects: this.hasModuleSideEffects(source, true),
 				syntheticNamedExports: false
 			};

test/function/samples/modify-meta/_config.js

@@ -0,0 +1,66 @@
+const assert = require('assert');
+const path = require('path');
+const ID_MAIN = path.join(__dirname, 'main.js');
+
+let initialMeta;
+
+module.exports = {
+	description: 'allows to freely modify moduleInfo.meta and maintain object identity',
+	options: {
+		plugins: [
+			{
+				name: 'first',
+				buildStart() {
+					this.load({ id: ID_MAIN });
+					initialMeta = this.getModuleInfo(ID_MAIN).meta;
+					initialMeta.buildStart = true;
+				},
+				load(id) {
+					assert.strictEqual(id, ID_MAIN);
+					const meta = this.getModuleInfo(ID_MAIN).meta;
+					assert.deepStrictEqual(meta, { buildStart: true }, 'load');
+					assert.strictEqual(meta, initialMeta);
+					meta.load1a = true;
+					return { code: `assert.ok(true);`, meta: { load1b: true } };
+				},
+				transform(code, id) {
+					assert.strictEqual(id, ID_MAIN);
+					const meta = this.getModuleInfo(ID_MAIN).meta;
+					assert.deepStrictEqual(
+						meta,
+						{ buildStart: true, load1a: true, load1b: true },
+						'transform'
+					);
+					assert.strictEqual(meta, initialMeta);
+					meta.transform1a = true;
+					return { code: `assert.ok(true);`, meta: { transform1b: true } };
+				},
+				buildEnd(error) {
+					if (error) {
+						throw error;
+					}
+					const meta = this.getModuleInfo(ID_MAIN).meta;
+					assert.deepStrictEqual(
+						meta,
+						{
+							buildStart: true,
+							load1a: true,
+							load1b: true,
+							transform1a: true,
+							transform1b: true,
+							transform2: true
+						},
+						'buildEnd'
+					);
+				}
+			},
+			{
+				name: 'second',
+				transform(code, id) {
+					assert.strictEqual(id, ID_MAIN);
+					return { code: `assert.ok(true);`, meta: { transform2: true } };
+				}
+			}
+		]
+	}
+};

test/function/samples/modify-meta/main.js

@@ -0,0 +1 @@
+assert.ok(true);

test/incremental/index.js

@@ -293,18 +293,17 @@ describe('incremental', () => {
 			},
 
 			load(id) {
-				assert.deepStrictEqual(this.getModuleInfo(id).meta, { test: { resolved: id } });
 				return { code: modules[id], meta: { test: { loaded: id } } };
 			},
 
 			transform(code, id) {
 				transformCalls++;
-				assert.deepStrictEqual(this.getModuleInfo(id).meta, { test: { loaded: id } });
+				assert.deepStrictEqual(this.getModuleInfo(id).meta, { test: { loaded: id } }, 'transform');
 				return { code, meta: { test: { transformed: id } } };
 			},
 
 			moduleParsed({ id, meta }) {
-				assert.deepStrictEqual(meta, { test: { transformed: id } });
+				assert.deepStrictEqual(meta, { test: { transformed: id } }, 'moduleParsed');
 				moduleParsedCalls++;
 			},
 
@@ -314,7 +313,8 @@ describe('incremental', () => {
 					[
 						{ id: 'entry', meta: { test: { transformed: 'entry' } } },
 						{ id: 'foo', meta: { test: { transformed: 'foo' } } }
-					]
+					],
+					'buildEnd'
 				);
 			}
 		};