Allow OnResolve plugins to mark modules as side effect free

Adding a SideEffectFree property to OnResolve that plugins
can set to indicate that the resolved module is side effect
free.

Fixes evanw#1009

Co-authored-by: Adam Gaynor <adamsg9425@gmail.com>

cmd/esbuild/service.go

@@ -715,6 +715,9 @@ func (service *serviceType) convertPlugins(key int, jsPlugins interface{}) ([]ap
 				if value, ok := response["external"]; ok {
 					result.External = value.(bool)
 				}
+				if value, ok := response["sideEffectFree"]; ok {
+					result.SideEffectFree = value.(bool)
+				}
 				if value, ok := response["pluginData"]; ok {
 					result.PluginData = value.(int)
 				}

internal/bundler/bundler.go

@@ -734,10 +734,18 @@ func runOnResolvePlugins(
 				return nil, true, resolver.DebugMeta{}
 			}
 
+			var sideEffectsData *resolver.SideEffectsData
+			if result.SideEffectFree {
+				sideEffectsData = &resolver.SideEffectsData{
+					IsSideEffectsArrayInJSON: false,
+				}
+			}
+
 			return &resolver.ResolveResult{
-				PathPair:   resolver.PathPair{Primary: result.Path},
-				IsExternal: result.External,
-				PluginData: result.PluginData,
+				PathPair:               resolver.PathPair{Primary: result.Path},
+				IsExternal:             result.External,
+				PluginData:             result.PluginData,
+				PrimarySideEffectsData: sideEffectsData,
 			}, false, resolver.DebugMeta{}
 		}
 	}

internal/bundler/bundler_dce_test.go

@@ -1,9 +1,11 @@
 package bundler
 
 import (
+	"regexp"
 	"testing"
 
 	"github.com/evanw/esbuild/internal/config"
+	"github.com/evanw/esbuild/internal/logger"
 )
 
 var dce_suite = suite{
@@ -1655,3 +1657,78 @@ func TestTreeShakingInESMWrapper(t *testing.T) {
 		},
 	})
 }
+
+func TestPackageJsonSideEffectsFalsePluginResolver(t *testing.T) {
+	pk2Index := `
+		export {default as Cmp1} from './cmp1.vue';
+		export {default as Cmp2} from './cmp2';
+	`
+
+	testPackageJsonSideEffectsFalsePluginResolver(t, pk2Index)
+}
+
+func TestPackageJsonSideEffectsFalseNoPlugins(t *testing.T) {
+	pk2Index := `
+		export {default as Cmp1} from './cmp1';
+		export {default as Cmp2} from './cmp2';
+	`
+
+	testPackageJsonSideEffectsFalsePluginResolver(t, pk2Index)
+}
+
+func testPackageJsonSideEffectsFalsePluginResolver(t *testing.T, pkg2Index string) {
+	t.Helper()
+
+	mockFiles := map[string]string{
+		"/Users/user/project/src/entry.js": `
+			import {Cmp2} from "demo-pkg2"
+			console.log(Cmp2);
+		`,
+		"/Users/user/project/node_modules/demo-pkg2/cmp1.js": `
+			import {__decorate} from './helper';
+			let Something = {}
+			__decorate(Something);
+			export default Something;
+		`,
+		"/Users/user/project/node_modules/demo-pkg2/cmp2.js": `
+			import {__decorate} from './helper';
+			class Something2 {}
+			__decorate(Something2);
+			export default Something2;
+		`,
+		"/Users/user/project/node_modules/demo-pkg2/helper.js": `
+			export function __decorate(s) {
+			}
+		`,
+		"/Users/user/project/node_modules/demo-pkg2/package.json": `
+			{
+				"sideEffects": false
+			}
+		`,
+		"/Users/user/project/node_modules/demo-pkg2/index.js": pkg2Index,
+	}
+
+	dce_suite.expectBundled(t, bundled{
+		files:      mockFiles,
+		entryPaths: []string{"/Users/user/project/src/entry.js"},
+		options: config.Options{
+			Mode:          config.ModeBundle,
+			AbsOutputFile: "/out.js",
+			Plugins: []config.Plugin{
+				{
+					OnResolve: []config.OnResolve{
+						{
+							Filter: regexp.MustCompile("\\.vue$"),
+							Callback: func(ora config.OnResolveArgs) config.OnResolveResult {
+								return config.OnResolveResult{
+									Path:           logger.Path{Text: "/Users/user/project/node_modules/demo-pkg2/cmp1.js"},
+									SideEffectFree: true,
+								}
+							},
+						},
+					},
+				},
+			},
+		},
+	})
+}

internal/bundler/snapshots/snapshots_dce.txt

@@ -414,6 +414,22 @@ console.log("hello");
 // Users/user/project/src/entry.js
 console.log(demo_pkg_exports);
 
+================================================================================
+TestPackageJsonSideEffectsFalseNoPlugins
+---------- /out.js ----------
+// Users/user/project/node_modules/demo-pkg2/helper.js
+function __decorate(s) {
+}
+
+// Users/user/project/node_modules/demo-pkg2/cmp2.js
+var Something2 = class {
+};
+__decorate(Something2);
+var cmp2_default = Something2;
+
+// Users/user/project/src/entry.js
+console.log(cmp2_default);
+
 ================================================================================
 TestPackageJsonSideEffectsFalseNoWarningInNodeModulesIssue999
 ---------- /out.js ----------
@@ -462,6 +478,22 @@ var init_a = __esm({
 // Users/user/project/src/entry.js
 Promise.resolve().then(() => (init_a(), a_exports)).then((x) => assert(x.foo === "foo"));
 
+================================================================================
+TestPackageJsonSideEffectsFalsePluginResolver
+---------- /out.js ----------
+// Users/user/project/node_modules/demo-pkg2/helper.js
+function __decorate(s) {
+}
+
+// Users/user/project/node_modules/demo-pkg2/cmp2.js
+var Something2 = class {
+};
+__decorate(Something2);
+var cmp2_default = Something2;
+
+// Users/user/project/src/entry.js
+console.log(cmp2_default);
+
 ================================================================================
 TestPackageJsonSideEffectsFalseRemoveBareImportCommonJS
 ---------- /out.js ----------

internal/config/config.go

@@ -490,9 +490,10 @@ type OnResolveArgs struct {
 type OnResolveResult struct {
 	PluginName string
 
-	Path       logger.Path
-	External   bool
-	PluginData interface{}
+	Path           logger.Path
+	External       bool
+	SideEffectFree bool
+	PluginData     interface{}
 
 	Msgs        []logger.Msg
 	ThrownError error

lib/shared/common.ts

@@ -780,6 +780,7 @@ export function createChannel(streamIn: StreamIn): StreamOut {
                 let path = getFlag(result, keys, 'path', mustBeString);
                 let namespace = getFlag(result, keys, 'namespace', mustBeString);
                 let external = getFlag(result, keys, 'external', mustBeBoolean);
+                let sideEffectFree = getFlag(result, keys, 'sideEffectFree', mustBeBoolean);
                 let pluginData = getFlag(result, keys, 'pluginData', canBeAnything);
                 let errors = getFlag(result, keys, 'errors', mustBeArray);
                 let warnings = getFlag(result, keys, 'warnings', mustBeArray);
@@ -792,6 +793,7 @@ export function createChannel(streamIn: StreamIn): StreamOut {
                 if (path != null) response.path = path;
                 if (namespace != null) response.namespace = namespace;
                 if (external != null) response.external = external;
+                if (sideEffectFree != null) response.sideEffectFree = sideEffectFree;
                 if (pluginData != null) response.pluginData = stash.store(pluginData);
                 if (errors != null) response.errors = sanitizeMessages(errors, 'errors', stash, name);
                 if (warnings != null) response.warnings = sanitizeMessages(warnings, 'warnings', stash, name);

lib/shared/stdio_protocol.ts

@@ -157,6 +157,7 @@ export interface OnResolveResponse {
 
   path?: string;
   external?: boolean;
+  sideEffectFree?: boolean;
   namespace?: string;
   pluginData?: number;
 

lib/shared/types.ts

@@ -241,6 +241,7 @@ export interface OnResolveResult {
 
   path?: string;
   external?: boolean;
+  sideEffectFree?: boolean;
   namespace?: string;
   pluginData?: any;
 

pkg/api/api.go

@@ -464,10 +464,11 @@ type OnResolveResult struct {
 	Errors   []Message
 	Warnings []Message
 
-	Path       string
-	External   bool
-	Namespace  string
-	PluginData interface{}
+	Path           string
+	External       bool
+	SideEffectFree bool
+	Namespace      string
+	PluginData     interface{}
 
 	WatchFiles []string
 	WatchDirs  []string

pkg/api/api_impl.go

@@ -1460,6 +1460,7 @@ func (impl *pluginImpl) OnResolve(options OnResolveOptions, callback func(OnReso
 
 			result.Path = logger.Path{Text: response.Path, Namespace: response.Namespace}
 			result.External = response.External
+			result.SideEffectFree = response.SideEffectFree
 			result.PluginData = response.PluginData
 
 			// Convert log messages

scripts/plugin-tests.js

@@ -709,6 +709,61 @@ let pluginTests = {
     assert.strictEqual(result.default, 123)
   },
 
+  async resolveWithSideEffectFree({ esbuild, testDir }) {
+    const input = path.join(testDir, 'in.js')
+    const cmp1 = path.join(testDir, 'cmp1.js')
+    const cmp2 = path.join(testDir, 'cmp2.js')
+    const cmpIndex = path.join(testDir, 'cmpIndex.js')
+    const helper = path.join(testDir, 'helper.js')
+
+    await writeFileAsync(input, `
+      import {Cmp2} from "./cmpIndex"
+			console.log(Cmp2);
+    `)
+    await writeFileAsync(cmp1, `
+      import {__decorate} from './helper';
+			let Something = {}
+			__decorate(Something);
+			export default Something;
+    `)
+    await writeFileAsync(cmp2, `
+      import {__decorate} from './helper';
+			let Something2 = {}
+			__decorate(Something2);
+			export default Something2;
+    `)
+    await writeFileAsync(cmpIndex, `
+      export {default as Cmp1} from './cmp1.vue';
+      export {default as Cmp2} from './cmp2';
+    `)
+    await writeFileAsync(helper, `
+      export function __decorate(s) {
+			}
+    `)
+
+    const result = await esbuild.build({
+      entryPoints: [input],
+      bundle: true,
+      write: false,
+      format: 'cjs',
+      plugins: [{
+        name: 'name',
+        setup(build) {
+          build.onResolve({ filter: /\.vue$/ }, async (args) => {
+            return {
+              path: path.join(args.resolveDir, args.path.replace('.vue', '.js')),
+              sideEffectFree: true,
+            };
+          });
+        },
+      }],
+    })
+
+    const output = result.outputFiles[0].text;
+
+    assert.doesNotMatch(output, /cmp1.js/);
+  },
+
   async noResolveDirInFileModule({ esbuild, testDir }) {
     const input = path.join(testDir, 'in.js')
     const output = path.join(testDir, 'out.js')