Support optional calls in no-unused-expressions

rules/no-unused-expressions.js

@@ -42,8 +42,22 @@ function isInDoStatement(node) {
   return false;
 }
 
+/**
+ * @param {ASTNode} node - any node
+ * @returns {boolean} whether the given node is an optional call expression,
+ * see https://github.com/tc39/proposal-optional-chaining
+ */
+function isOptionalCallExpression(node) {
+  return (
+    !!node &&
+    node.type === 'ExpressionStatement' &&
+    node.expression.type === 'OptionalCallExpression'
+  );
+}
+
 module.exports = ruleComposer.filterReports(
   rule,
-  (problem, metadata) => !isInDoStatement(problem.node)
+  (problem, metadata) =>
+    !isInDoStatement(problem.node) && !isOptionalCallExpression(problem.node)
 );
 

tests/rules/no-unused-expressions.js

@@ -74,12 +74,13 @@ ruleTester.run("no-unused-expressions", rule, {
         },
 
         // Babel-specific test cases.
-      "let a = do { if (foo) { foo.bar } }",
-      "let a = do { foo }",
-      "let a = do { let b = 2; foo; }",
-      "let a = do { (foo + 1) }",
-      "let a = do { if (foo) { if (foo.bar) { foo.bar } } }",
-      "let a = do { if (foo) { if (foo.bar) { foo.bar } else if (foo.baz) { foo.baz } } }",
+        "let a = do { if (foo) { foo.bar } }",
+        "let a = do { foo }",
+        "let a = do { let b = 2; foo; }",
+        "let a = do { (foo + 1) }",
+        "let a = do { if (foo) { if (foo.bar) { foo.bar } } }",
+        "let a = do { if (foo) { if (foo.bar) { foo.bar } else if (foo.baz) { foo.baz } } }",
+        "foo.bar?.();",
 
     ],
     invalid: [
@@ -136,7 +137,7 @@ ruleTester.run("no-unused-expressions", rule, {
         },
 
         // Babel-specific test cases.
-      { code: "let a = do { foo; let b = 2; }", errors: [{ message: "Expected an assignment or function call and instead saw an expression.", type: "ExpressionStatement" }] },
+        { code: "let a = do { foo; let b = 2; }", errors: [{ message: "Expected an assignment or function call and instead saw an expression.", type: "ExpressionStatement" }] },
         { code: "let a = do { if (foo) { foo.bar } else { a; bar.foo } }", errors: [{ message: "Expected an assignment or function call and instead saw an expression.", type: "ExpressionStatement" }] },
 
     ]