method call is assumed to mutate method owner (#13)

src/Statement.js

@@ -188,6 +188,11 @@ export default class Statement {
 
 		else if ( node.type === 'CallExpression' ) {
 			node.arguments.forEach( arg => addNode( arg, false ) );
+
+			// `foo.bar()` is assumed to mutate foo
+			if ( node.callee.type === 'MemberExpression' ) {
+				addNode( node.callee );
+			}
 		}
 	}
 

test/function/method-call-mutates-this/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'method calls are assumed to mutate the owner'
+};

test/function/method-call-mutates-this/foo.js

@@ -0,0 +1,15 @@
+var obj = {
+	set: function ( key, value ) {
+		this[ key ] = value;
+	},
+
+	get: function ( key ) {
+		return this[ key ];
+	}
+};
+
+obj.set( 'answer', 42 );
+
+export default function ( key ) {
+	return obj.get( key );
+}

test/function/method-call-mutates-this/main.js

@@ -0,0 +1,3 @@
+import foo from './foo';
+
+assert.equal( foo( 'answer' ), 42 );