fix: false positive for optional call expressions in no-unused-expressions (#448)

Author: bradzacher

.README/rules/no-unused-expressions.md

@@ -1,7 +1,7 @@
 ### `no-unused-expressions`
 
 An extension of [ESLint's `no-unused-expressions`](https://eslint.org/docs/rules/no-unused-expressions).
-This rule ignores type cast expressions, but otherwise behaves the same as ESLint's
+This rule ignores type cast expressions and optional call expressions, but otherwise behaves the same as ESLint's
 `no-unused-expressions`.
 
 Bare type casts are useful, for example to assert the exhaustiveness of a `switch`:

src/rules/noUnusedExpressions.js

@@ -10,9 +10,13 @@ const create = (context) => {
 
   return {
     ExpressionStatement (node) {
-      if (node.expression.type !== 'TypeCastExpression') {
-        coreChecks.ExpressionStatement(node);
+      if (
+        node.expression.type === 'TypeCastExpression' ||
+        node.expression.type === 'OptionalCallExpression'
+      ) {
+        return;
       }
+      coreChecks.ExpressionStatement(node);
     },
   };
 };

tests/rules/assertions/noUnusedExpressions.js

@@ -6,10 +6,19 @@ export default {
         message: 'Expected an assignment or function call and instead saw an expression.',
       }],
     },
+    {
+      code: 'x?.y',
+      errors: [{
+        message: 'Expected an assignment or function call and instead saw an expression.',
+      }],
+    },
   ],
   valid: [
     {
       code: '(foo: number)',
     },
+    {
+      code: 'x?.y()',
+    },
   ],
 };