fix(no-expression-statements): allow yield expressions (#570)

Author: RebeccaStevens

src/rules/no-expression-statements.ts

@@ -7,7 +7,7 @@ import { shouldIgnorePattern, ignorePatternOptionSchema } from "~/options";
 import { isDirectivePrologue } from "~/utils/misc";
 import type { RuleResult, NamedCreateRuleMetaWithCategory } from "~/utils/rule";
 import { createRule, getTypeOfNode } from "~/utils/rule";
-import { isVoidType } from "~/utils/type-guards";
+import { isVoidType, isYieldExpression } from "~/utils/type-guards";
 
 /**
  * The name of this rule.
@@ -86,8 +86,8 @@ function checkExpressionStatement(
     };
   }
 
-  // Allow specifying directive prologues.
-  if (isDirectivePrologue(node)) {
+  // Allow specifying directive prologues and using yield expressions.
+  if (isDirectivePrologue(node) || isYieldExpression(node.expression)) {
     return {
       context,
       descriptors: [],

src/utils/type-guards.ts

@@ -346,6 +346,12 @@ export function isVariableDeclarator(
   return node.type === AST_NODE_TYPES.VariableDeclarator;
 }
 
+export function isYieldExpression(
+  node: TSESTree.Node
+): node is TSESTree.YieldExpression {
+  return node.type === AST_NODE_TYPES.YieldExpression;
+}
+
 export function hasID(
   node: TSESTree.Node
 ): node is Extract<TSESTree.Node, { id: unknown }> {

tests/rules/no-expression-statement/es6/index.ts

@@ -0,0 +1,7 @@
+import invalid from "./invalid";
+import valid from "./valid";
+
+export default {
+  valid,
+  invalid,
+};

tests/rules/no-expression-statement/es6/invalid.ts

@@ -0,0 +1,7 @@
+import dedent from "dedent";
+
+import type { InvalidTestCase } from "~/tests/helpers/util";
+
+const tests: InvalidTestCase[] = [];
+
+export default tests;

tests/rules/no-expression-statement/es6/valid.ts

@@ -0,0 +1,18 @@
+import dedent from "dedent";
+
+import type { ValidTestCase } from "~/tests/helpers/util";
+
+const tests: ValidTestCase[] = [
+  // Allow yield.
+  {
+    code: dedent`
+      export function* foo() {
+        yield "hello";
+        return "world";
+      }
+    `,
+    optionsSet: [[]],
+  },
+];
+
+export default tests;

tests/rules/no-expression-statement/index.test.ts

@@ -2,9 +2,12 @@ import { name, rule } from "~/rules/no-expression-statements";
 import { testUsing } from "~/tests/helpers/testers";
 
 import es3Tests from "./es3";
+import es6Tests from "./es6";
 import tsTests from "./ts";
 
 testUsing.typescript(name, rule, tsTests);
+testUsing.typescript(name, rule, es6Tests);
 testUsing.typescript(name, rule, es3Tests);
 
 testUsing.es3(name, rule, es3Tests);
+testUsing.es6(name, rule, es6Tests);