Add option to control unknown global side effects

docs/999-big-list-of-options.md

@@ -802,7 +802,7 @@ Default: `false`
 If this option is provided, bundling will not fail if bindings are imported from a file that does not define these bindings. Instead, new variables will be created for these bindings with the value `undefined`.
 
 #### treeshake
-Type: `boolean | { annotations?: boolean, moduleSideEffects?: ModuleSideEffectsOption, propertyReadSideEffects?: boolean }`<br>
+Type: `boolean | { annotations?: boolean, moduleSideEffects?: ModuleSideEffectsOption, propertyReadSideEffects?: boolean, tryCatchDeoptimization?: boolean, unknownGlobalSideEffects?: boolean }`<br>
 CLI: `--treeshake`/`--no-treeshake`<br>
 Default: `true`
 
@@ -938,6 +938,29 @@ test(otherFn);
 
 ```
 
+**treeshake.unknownGlobalSideEffects**
+Type: `boolean`<br>
+CLI: `--treeshake.unknownGlobalSideEffects`/`--no-treeshake.unknownGlobalSideEffects`<br>
+Default: `true`
+
+Since accessing a non-existing global variable will throw an error, Rollup does by default retain any accesses to non-builtin global variables. Set this option to `false` to avoid this check.
+
+```js
+// input
+const jQuery = $;
+const requestTimeout = setTimeout;
+const element = angular.element;
+
+// output with unknownGlobalSideEffects == true
+const jQuery = $;
+const element = angular.element;
+
+// output with unknownGlobalSideEffects == false
+const element = angular.element;
+```
+
+In the example, the last line is always retained as accessing the `element` property could also throw an error if angular is e.g. `null`. To avoid this check, set `treeshake.propertyReadSideEffects` to `false` as well.
+
 ### Experimental options
 
 These options reflect new features that have not yet been fully finalized. Availability, behaviour and usage may therefore be subject to change between minor versions.

src/Graph.ts

@@ -116,13 +116,16 @@ export default class Graph {
 							(options.treeshake as TreeshakingOptions).propertyReadSideEffects !== false,
 						pureExternalModules: (options.treeshake as TreeshakingOptions).pureExternalModules,
 						tryCatchDeoptimization:
-							(options.treeshake as TreeshakingOptions).tryCatchDeoptimization !== false
+							(options.treeshake as TreeshakingOptions).tryCatchDeoptimization !== false,
+						unknownGlobalSideEffects:
+							(options.treeshake as TreeshakingOptions).unknownGlobalSideEffects !== false
 				  }
 				: {
 						annotations: true,
 						moduleSideEffects: true,
 						propertyReadSideEffects: true,
-						tryCatchDeoptimization: true
+						tryCatchDeoptimization: true,
+						unknownGlobalSideEffects: true
 				  };
 			if (typeof this.treeshakingOptions.pureExternalModules !== 'undefined') {
 				this.warnDeprecation(

src/Module.ts

@@ -110,6 +110,7 @@ export interface AstContext {
 	traceVariable: (name: string) => Variable | null;
 	treeshake: boolean;
 	tryCatchDeoptimization: boolean;
+	unknownGlobalSideEffects: boolean;
 	usesTopLevelAwait: boolean;
 	warn: (warning: RollupWarning, pos: number) => void;
 	warnDeprecation: (deprecation: string | RollupWarning, activeDeprecation: boolean) => void;
@@ -605,6 +606,8 @@ export default class Module {
 			treeshake: !!this.graph.treeshakingOptions,
 			tryCatchDeoptimization: (!this.graph.treeshakingOptions ||
 				this.graph.treeshakingOptions.tryCatchDeoptimization) as boolean,
+			unknownGlobalSideEffects: (!this.graph.treeshakingOptions ||
+				this.graph.treeshakingOptions.unknownGlobalSideEffects) as boolean,
 			usesTopLevelAwait: false,
 			warn: this.warn.bind(this),
 			warnDeprecation: this.graph.warnDeprecation.bind(this.graph)

src/ast/nodes/Identifier.ts

@@ -102,8 +102,8 @@ export default class Identifier extends NodeBase implements PatternNode {
 	}
 
 	hasEffects(): boolean {
-		// TODO Lukas observe the option here
 		return (
+			this.context.unknownGlobalSideEffects &&
 			this.variable instanceof GlobalVariable &&
 			this.variable.hasEffectsWhenAccessedAtPath(EMPTY_PATH)
 		);

src/rollup/types.d.ts

@@ -385,6 +385,7 @@ export interface TreeshakingOptions {
 	/** @deprecated Use `moduleSideEffects` instead */
 	pureExternalModules?: PureModulesOption;
 	tryCatchDeoptimization?: boolean;
+	unknownGlobalSideEffects?: boolean;
 }
 
 export type GetManualChunk = (id: string) => string | null | undefined;

test/form/samples/ignore-unknown-global-side-effects/_config.js

@@ -0,0 +1,10 @@
+module.exports = {
+	description:
+		'ignore side-effects when accessing unknown globals if treeshake.unknownGlobalSideEffects is false',
+	expectedWarnings: ['EMPTY_BUNDLE'],
+	options: {
+		treeshake: {
+			unknownGlobalSideEffects: false
+		}
+	}
+};

test/form/samples/ignore-unknown-global-side-effects/_expected.js

@@ -0,0 +1 @@
+

test/form/samples/ignore-unknown-global-side-effects/main.js

@@ -0,0 +1,2 @@
+foo;
+class bar extends baz {}