feat(rome_js_analyze): noUselessEmptyExport (#4693)

CHANGELOG.md

@@ -139,6 +139,10 @@ if no error diagnostics are emitted.
 
 	This rule disallows `\8` and `\9` escape sequences in string literals.
 
+- Add [`noUselessEmptyExport`](https://docs.rome.tools/lint/rules/noUselessEmptyExport/)
+
+	This rule disallows useless `export {}`.
+
 #### Other changes
 
 - Add new TypeScript globals (`AsyncDisposable`, `Awaited`, `DecoratorContext`, and others) [4643](https://github.com/rome/tools/issues/4643).

crates/rome_diagnostics_categories/src/categories.rs

@@ -93,6 +93,7 @@ define_categories! {
     "lint/nursery/noRedundantRoles": "https://docs.rome.tools/lint/rules/noRedundantRoles",
     "lint/nursery/noSelfAssign": "https://docs.rome.tools/lint/rules/noSelfAssign",
     "lint/nursery/noStaticOnlyClass": "https://docs.rome.tools/lint/rules/noStaticOnlyClass",
+    "lint/nursery/noUselessEmptyExport": "https://docs.rome.tools/lint/rules/noUselessEmptyExport",
     "lint/nursery/noVoid": "https://docs.rome.tools/lint/rules/noVoid",
     "lint/nursery/useAriaPropTypes": "https://docs.rome.tools/lint/rules/useAriaPropTypes",
     "lint/nursery/useArrowFunction": "https://docs.rome.tools/lint/rules/useArrowFunction",

crates/rome_js_analyze/src/analyzers/nursery/no_useless_empty_export.rs

@@ -0,0 +1,125 @@
+use rome_analyze::{context::RuleContext, declare_rule, ActionCategory, Ast, Rule, RuleDiagnostic};
+use rome_console::markup;
+use rome_diagnostics::Applicability;
+use rome_js_syntax::{AnyJsModuleItem, JsExport, JsModuleItemList, JsSyntaxToken};
+use rome_rowan::{AstNode, AstSeparatedList, BatchMutationExt};
+
+use crate::JsRuleAction;
+
+declare_rule! {
+    /// Disallow empty exports that don't change anything in a module file.
+    ///
+    /// An empty `export {}` is sometimes useful to turn a file that would otherwise be a script into a module.
+    /// Per the [TypeScript Handbook Modules page](https://www.typescriptlang.org/docs/handbook/modules.html):
+    ///
+    /// > In TypeScript, just as in ECMAScript 2015,
+    /// > any file containing a top-level import or export is considered a module.
+    /// > Conversely, a file without any top-level import or export declarations is treated as a script
+    /// > whose contents are available in the global scope.
+    ///
+    /// However, an `export {}` statement does nothing if there are any other top-level import or export in the file.
+    ///
+    /// Source: https://typescript-eslint.io/rules/no-useless-empty-export/
+    ///
+    /// ## Examples
+    ///
+    /// ### Invalid
+    ///
+    /// ```js,expect_diagnostic
+    /// import { A } from "module";
+    /// export {};
+    /// ```
+    ///
+    /// ```js,expect_diagnostic
+    /// export const A = 0;
+    /// export {};
+    /// ```
+    ///
+    /// ## Valid
+    ///
+    /// ```js
+    /// export {};
+    /// ```
+    ///
+    pub(crate) NoUselessEmptyExport {
+        version: "next",
+        name: "noUselessEmptyExport",
+        recommended: true,
+    }
+}
+
+impl Rule for NoUselessEmptyExport {
+    type Query = Ast<JsExport>;
+    /// The first import or export that makes useless the empty export.
+    type State = JsSyntaxToken;
+    type Signals = Option<Self::State>;
+    type Options = ();
+
+    fn run(ctx: &RuleContext<Self>) -> Self::Signals {
+        let node = ctx.query();
+        if is_empty_export(node) {
+            let module_item_list = JsModuleItemList::cast(node.syntax().parent()?)?;
+            // allow reporting an empty export that precedes another empty export.
+            let mut ignore_empty_export = true;
+            for module_item in module_item_list {
+                match module_item {
+                    AnyJsModuleItem::AnyJsStatement(_) => {}
+                    AnyJsModuleItem::JsImport(import) => return import.import_token().ok(),
+                    AnyJsModuleItem::JsExport(export) => {
+                        if !is_empty_export(&export) {
+                            return export.export_token().ok();
+                        }
+                        if !ignore_empty_export {
+                            return export.export_token().ok();
+                        }
+                        if node == &export {
+                            ignore_empty_export = false
+                        }
+                    }
+                }
+            }
+        }
+        None
+    }
+
+    fn diagnostic(ctx: &RuleContext<Self>, token: &Self::State) -> Option<RuleDiagnostic> {
+        Some(
+            RuleDiagnostic::new(
+                rule_category!(),
+                ctx.query().range(),
+                markup! {
+                    "This empty "<Emphasis>"export"</Emphasis>" is useless because there's another "<Emphasis>"export"</Emphasis>" or "<Emphasis>"import"</Emphasis>"."
+                },
+            ).detail(token.text_trimmed_range(), markup! {
+                "This "<Emphasis>{token.text_trimmed()}</Emphasis>" makes useless the empty export."
+            }),
+        )
+    }
+
+    fn action(ctx: &RuleContext<Self>, _: &Self::State) -> Option<JsRuleAction> {
+        let mut mutation = ctx.root().begin();
+        mutation.remove_node(ctx.query().clone());
+        Some(JsRuleAction {
+            category: ActionCategory::QuickFix,
+            applicability: Applicability::Always,
+            message: markup! { "Remove this useless empty export." }.to_owned(),
+            mutation,
+        })
+    }
+}
+
+fn is_empty_export(export: &JsExport) -> bool {
+    (|| -> Option<bool> {
+        Some(
+            export
+                .export_clause()
+                .ok()?
+                .as_js_export_named_clause()?
+                .specifiers()
+                .iter()
+                .count()
+                == 0,
+        )
+    })()
+    .unwrap_or(false)
+}

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_default_export.js

@@ -0,0 +1,2 @@
+export default {};
+export {}

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_default_export.js.snap

@@ -0,0 +1,35 @@
+---
+source: crates/rome_js_analyze/tests/spec_tests.rs
+expression: invalid_with_default_export.js
+---
+# Input
+```js
+export default {};
+export {}
+```
+
+# Diagnostics
+```
+invalid_with_default_export.js:2:1 lint/nursery/noUselessEmptyExport  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━
+
+  ! This empty export is useless because there's another export or import.
+  
+    1 │ export default {};
+  > 2 │ export {}
+      │ ^^^^^^^^^
+  
+  i This export makes useless the empty export.
+  
+  > 1 │ export default {};
+      │ ^^^^^^
+    2 │ export {}
+  
+  i Safe fix: Remove this useless empty export.
+  
+    1 1 │   export default {};
+    2   │ - export·{}
+  
+
+```
+
+

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_empty_export.js

@@ -0,0 +1,2 @@
+export {}
+export {}

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_empty_export.js.snap

@@ -0,0 +1,34 @@
+---
+source: crates/rome_js_analyze/tests/spec_tests.rs
+expression: invalid_with_empty_export.js
+---
+# Input
+```js
+export {}
+export {}
+```
+
+# Diagnostics
+```
+invalid_with_empty_export.js:1:1 lint/nursery/noUselessEmptyExport  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━
+
+  ! This empty export is useless because there's another export or import.
+  
+  > 1 │ export {}
+      │ ^^^^^^^^^
+    2 │ export {}
+  
+  i This export makes useless the empty export.
+  
+    1 │ export {}
+  > 2 │ export {}
+      │ ^^^^^^
+  
+  i Safe fix: Remove this useless empty export.
+  
+    1 │ export·{}
+      │ ---------
+
+```
+
+

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_export.js

@@ -0,0 +1,3 @@
+function f() { return 0 }
+export const A = f();
+export {}

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_export.js.snap

@@ -0,0 +1,39 @@
+---
+source: crates/rome_js_analyze/tests/spec_tests.rs
+expression: invalid_with_export.js
+---
+# Input
+```js
+function f() { return 0 }
+export const A = f();
+export {}
+```
+
+# Diagnostics
+```
+invalid_with_export.js:3:1 lint/nursery/noUselessEmptyExport  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  ! This empty export is useless because there's another export or import.
+  
+    1 │ function f() { return 0 }
+    2 │ export const A = f();
+  > 3 │ export {}
+      │ ^^^^^^^^^
+  
+  i This export makes useless the empty export.
+  
+    1 │ function f() { return 0 }
+  > 2 │ export const A = f();
+      │ ^^^^^^
+    3 │ export {}
+  
+  i Safe fix: Remove this useless empty export.
+  
+    1 1 │   function f() { return 0 }
+    2 2 │   export const A = f();
+    3   │ - export·{}
+  
+
+```
+
+

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_export_from.js

@@ -0,0 +1,2 @@
+export * from "mod";
+export {}

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_export_from.js.snap

@@ -0,0 +1,35 @@
+---
+source: crates/rome_js_analyze/tests/spec_tests.rs
+expression: invalid_with_export_from.js
+---
+# Input
+```js
+export * from "mod";
+export {}
+```
+
+# Diagnostics
+```
+invalid_with_export_from.js:2:1 lint/nursery/noUselessEmptyExport  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━
+
+  ! This empty export is useless because there's another export or import.
+  
+    1 │ export * from "mod";
+  > 2 │ export {}
+      │ ^^^^^^^^^
+  
+  i This export makes useless the empty export.
+  
+  > 1 │ export * from "mod";
+      │ ^^^^^^
+    2 │ export {}
+  
+  i Safe fix: Remove this useless empty export.
+  
+    1 1 │   export * from "mod";
+    2   │ - export·{}
+  
+
+```
+
+

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_import.js

@@ -0,0 +1,3 @@
+import { A } from "mod"
+function f() { return 0 }
+export {}

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_import.js.snap

@@ -0,0 +1,39 @@
+---
+source: crates/rome_js_analyze/tests/spec_tests.rs
+expression: invalid_with_import.js
+---
+# Input
+```js
+import { A } from "mod"
+function f() { return 0 }
+export {}
+```
+
+# Diagnostics
+```
+invalid_with_import.js:3:1 lint/nursery/noUselessEmptyExport  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  ! This empty export is useless because there's another export or import.
+  
+    1 │ import { A } from "mod"
+    2 │ function f() { return 0 }
+  > 3 │ export {}
+      │ ^^^^^^^^^
+  
+  i This import makes useless the empty export.
+  
+  > 1 │ import { A } from "mod"
+      │ ^^^^^^
+    2 │ function f() { return 0 }
+    3 │ export {}
+  
+  i Safe fix: Remove this useless empty export.
+  
+    1 1 │   import { A } from "mod"
+    2 2 │   function f() { return 0 }
+    3   │ - export·{}
+  
+
+```
+
+

crates/rome_js_analyze/tests/specs/nursery/noUselessEmptyExport/invalid_with_sideeffect_import.js

@@ -0,0 +1,3 @@
+import "mod"
+function f() { return 0 }
+export {}