unify APIs

src/Declaration.js

@@ -43,7 +43,7 @@ export default class Declaration {
 		if ( this.tested ) return this.hasSideEffects;
 		this.tested = true;
 
-		if ( !this.statement || !this.functionNode ) {
+		if ( !this.functionNode ) {
 			this.hasSideEffects = true; // err on the side of caution. TODO handle unambiguous `var x; x = y => z` cases
 		} else {
 			this.hasSideEffects = run( this.functionNode.body, this.functionNode._scope, this.statement, strongDependencies, false, safe );
@@ -224,6 +224,10 @@ export class ExternalDeclaration {
 		return es6 ? this.name : `${this.module.name}.${this.name}`;
 	}
 
+	run ( strongDependencies, safe ) {
+		return safe;
+	}
+
 	use () {
 		// noop?
 	}

src/utils/run.js

@@ -83,7 +83,7 @@ export default function run ( node, scope, statement, strongDependencies, force,
 					                    statement.module.trace( node.callee.name );
 
 					if ( declaration ) {
-						if ( declaration.isExternal || declaration.run( strongDependencies, safe ) ) {
+						if ( declaration.run( strongDependencies, safe ) ) {
 							hasSideEffect = true;
 						}
 					} else if ( safe && !pureFunctions[ node.callee.name ] ) {
@@ -104,7 +104,7 @@ export default function run ( node, scope, statement, strongDependencies, force,
 						}
 					} else {
 						// is not a keypath like `foo.bar.baz` – could be e.g.
-						// `(a || b).foo()`. Err on the side of caution
+						// `foo[bar].baz()`. Err on the side of caution
 						hasSideEffect = true;
 					}
 				}