rome · ematipico · Jan 5, 2023 · Dec 11, 2022 · Dec 11, 2022 · Dec 11, 2022
diff --git a/crates/rome_diagnostics_categories/src/categories.rs b/crates/rome_diagnostics_categories/src/categories.rs
@@ -93,6 +93,7 @@ define_dategories! {
     "lint/nursery/useValidForDirection": "https://docs.rome.tools/lint/rules/useValidForDirection",
     "lint/nursery/useHookAtTopLevel": "https://docs.rome.tools/lint/rules/useHookAtTopLevel",
     "lint/nursery/noDuplicateJsxProps": "https://docs.rome.tools/lint/rules/noDuplicateJsxProps",
+    "lint/nursery/useYield": "https://docs.rome.tools/lint/rules/useYield",
     // Insert new nursery rule here
 
     // performance

diff --git a/crates/rome_js_analyze/src/analyzers/nursery.rs b/crates/rome_js_analyze/src/analyzers/nursery.rs
diff --git a/crates/rome_js_analyze/src/analyzers/nursery/use_yield.rs b/crates/rome_js_analyze/src/analyzers/nursery/use_yield.rs
@@ -0,0 +1,180 @@
+use rome_analyze::context::RuleContext;
+use rome_analyze::{
+    declare_rule, AddVisitor, Phases, QueryMatch, Queryable, Rule, RuleDiagnostic, ServiceBag,
+    Visitor, VisitorContext,
+};
+use rome_console::markup;
+use rome_js_syntax::{
+    AnyJsFunction, JsLanguage, JsMethodClassMember, JsMethodObjectMember, JsStatementList,
+    JsYieldExpression, TextRange, WalkEvent,
+};
+use rome_rowan::{declare_node_union, AstNode, AstNodeList, Language, SyntaxNode};
+
+declare_rule! {
+    /// Require generator functions to contain `yield`.
+    ///
+    /// This rule generates warnings for generator functions that do not have the `yield` keyword.
+    ///
+    /// Source: [require-await](https://eslint.org/docs/latest/rules/require-yield).
+    ///
+    /// ## Examples
+    ///
+    /// ### Invalid
+    ///
+    /// ```js,expect_diagnostic
+    /// function* foo() {
+    ///   return 10;
+    /// }
+    /// ```
+    ///
+    /// ### Valid
+    /// ```js
+    /// function* foo() {
+    ///   yield 5;
+    ///   return 10;
+    /// }
+    ///
+    /// function foo() {
+    ///   return 10;
+    /// }
+    ///
+    /// // This rule does not warn on empty generator functions.
+    /// function* foo() { }
+    /// ```
+    pub(crate) UseYield {
+        version: "next",
+        name: "useYield",
+        recommended: true,
+    }
+}
+
+declare_node_union! {
+    pub(crate) AnyFunctionLike = AnyJsFunction | JsMethodObjectMember | JsMethodClassMember
+}
+
+impl AnyFunctionLike {
+    fn is_generator(&self) -> bool {
+        match self {
+            AnyFunctionLike::AnyJsFunction(any_js_function) => any_js_function.is_generator(),
+            AnyFunctionLike::JsMethodClassMember(method_class_member) => {
+                method_class_member.star_token().is_some()
+            }
+            AnyFunctionLike::JsMethodObjectMember(method_obj_member) => {
+                method_obj_member.star_token().is_some()
+            }
+        }
+    }
+
+    fn statements(&self) -> Option<JsStatementList> {
+        Some(match self {
+            AnyFunctionLike::AnyJsFunction(any_js_function) => any_js_function
+                .body()
+                .ok()?
+                .as_js_function_body()?
+                .statements(),
+            AnyFunctionLike::JsMethodClassMember(method_class_member) => {
+                method_class_member.body().ok()?.statements()
+            }
+            AnyFunctionLike::JsMethodObjectMember(method_obj_member) => {
+                method_obj_member.body().ok()?.statements()
+            }
+        })
+    }
+}
+
+#[derive(Default)]
+struct MissingYieldVisitor {
+    /// Vector to hold a function node and a boolean indicating whether the function
+    /// contains an `yield` expression or not.
+    stack: Vec<(AnyFunctionLike, bool)>,
+}
+
+impl Visitor for MissingYieldVisitor {
+    type Language = JsLanguage;
+
+    fn visit(
+        &mut self,
+        event: &WalkEvent<SyntaxNode<Self::Language>>,
+        mut ctx: VisitorContext<Self::Language>,
+    ) {
+        match event {
+            WalkEvent::Enter(node) => {
+                // When the visitor enters a function node, push a new entry on the stack
+                if let Some(node) = AnyFunctionLike::cast_ref(node) {
+                    self.stack.push((node, false));
+                }
+
+                if JsYieldExpression::can_cast(node.kind()) {
+                    // When the visitor enters a `yield` expression, set the
+                    // `has_yield` flag for the top entry on the stack to `true`
+                    if let Some((_, has_yield)) = self.stack.last_mut() {
+                        *has_yield = true;
+                    }
+                }
+            }
+            WalkEvent::Leave(node) => {
+                // When the visitor exits a function, if it matches the node of the top-most
+                // entry of the stack and the `has_yield` flag is `false`, emit a query match
+                if let Some(exit_node) = AnyFunctionLike::cast_ref(node) {
+                    if let Some((enter_node, has_yield)) = self.stack.pop() {
+                        if enter_node == exit_node && !has_yield {
+                            ctx.match_query(MissingYield(enter_node));
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+pub(crate) struct MissingYield(AnyFunctionLike);
+
+impl QueryMatch for MissingYield {
+    fn text_range(&self) -> TextRange {
+        self.0.range()
+    }
+}
+
+impl Queryable for MissingYield {
+    type Input = Self;
+    type Language = JsLanguage;
+    type Output = AnyFunctionLike;
+    type Services = ();
+
+    fn build_visitor(
+        analyzer: &mut impl AddVisitor<Self::Language>,
+        _: &<Self::Language as Language>::Root,
+    ) {
+        analyzer.add_visitor(Phases::Syntax, MissingYieldVisitor::default);
+    }
+
+    fn unwrap_match(_: &ServiceBag, query: &Self::Input) -> Self::Output {
+        query.0.clone()
+    }
+}
+
+impl Rule for UseYield {
+    type Query = MissingYield;
+    type State = ();
+    type Signals = Option<Self::State>;
+    type Options = ();
+
+    fn run(ctx: &RuleContext<Self>) -> Self::Signals {
+        let query = ctx.query();
+
+        // Don't emit diagnostic for non-generators or generators with an empty body
+        if !query.is_generator() || query.statements()?.is_empty() {
+            return None;
+        }
+
+        Some(())
+    }
+
+    fn diagnostic(ctx: &RuleContext<Self>, _: &Self::State) -> Option<RuleDiagnostic> {
+        Some(RuleDiagnostic::new(
+            rule_category!(),
+            ctx.query().range(),
+            markup! {"This generator function doesn't contain "<Emphasis>"yield"</Emphasis>"."},
+        ))
+    }
+}
diff --git a/crates/rome_js_analyze/tests/specs/nursery/useYield.js b/crates/rome_js_analyze/tests/specs/nursery/useYield.js
@@ -0,0 +1,93 @@
+// Valid
+function foo() {
+	return 0;
+}
+
+function* foo() {
+	yield 0;
+}
+
+function* foo() {}
+
+(function* foo() {
+	yield 0;
+})();
+
+(function* foo() {})();
+
+const obj = {
+	*foo() {
+		yield 0;
+	},
+};
+
+const obj = { *foo() {} };
+
+class A {
+	*foo() {
+		yield 0;
+	}
+}
+
+class A {
+	*foo() {}
+}
+
+// Invalid
+function* foo() {
+	return 0;
+}
+
+(function* foo() {
+	return 0;
+})();
+
+const obj = {
+	*foo() {
+		return 0;
+	},
+};
+
+class A {
+	*foo() {
+		return 0;
+	}
+}
+
+function* foo() {
+	function* bar() {
+		yield 0;
+	}
+}
+
+function* foo() {
+	function* bar() {
+		return 0;
+	}
+	yield 0;
+}
+
+function* foo() {
+	function* bar() {
+		yield 0;
+	}
+	return 0;
+}
+
+function* foo() {
+	const obj = {
+		*bar() {
+			return 0;
+		},
+	};
+
+	class A {
+		*baz() {
+			return 0;
+		}
+	}
+
+	if (a === 'a') {
+		yield 0;
+	}
+}