feat(linter) eslint plugin unicorn: no useless fallback (#1176)

crates/oxc_linter/src/ast_util.rs

@@ -244,6 +244,26 @@ pub fn outermost_paren<'a, 'b>(node: &'b AstNode<'a>, ctx: &'b LintContext<'a>)
     node
 }
 
+pub fn outermost_paren_parent<'a, 'b>(
+    node: &'b AstNode<'a>,
+    ctx: &'b LintContext<'a>,
+) -> Option<&'b AstNode<'a>> {
+    let mut node = node;
+
+    loop {
+        if let Some(parent) = ctx.nodes().parent_node(node.id()) {
+            if let AstKind::ParenthesizedExpression(_) = parent.kind() {
+                node = parent;
+                continue;
+            }
+        }
+
+        break;
+    }
+
+    ctx.nodes().parent_node(node.id())
+}
+
 pub fn get_name_from_property_key(key: &PropertyKey<'_>) -> Option<Atom> {
     match key {
         PropertyKey::Identifier(ident) => Some(ident.name.clone()),

crates/oxc_linter/src/rules.rs

@@ -154,6 +154,7 @@ mod unicorn {
     pub mod no_static_only_class;
     pub mod no_thenable;
     pub mod no_unnecessary_await;
+    pub mod no_useless_fallback_in_spread;
     pub mod prefer_add_event_listener;
     pub mod prefer_array_flat_map;
     pub mod prefer_blob_reading_methods;
@@ -289,6 +290,7 @@ oxc_macros::declare_all_lint_rules! {
     unicorn::no_static_only_class,
     unicorn::no_thenable,
     unicorn::no_unnecessary_await,
+    unicorn::no_useless_fallback_in_spread,
     unicorn::prefer_add_event_listener,
     unicorn::prefer_array_flat_map,
     unicorn::prefer_blob_reading_methods,

crates/oxc_linter/src/rules/unicorn/no_useless_fallback_in_spread.rs

@@ -0,0 +1,128 @@
+use oxc_ast::{ast::Expression, AstKind};
+use oxc_diagnostics::{
+    miette::{self, Diagnostic},
+    thiserror::Error,
+};
+use oxc_macros::declare_oxc_lint;
+use oxc_span::Span;
+use oxc_syntax::operator::LogicalOperator;
+
+use crate::{ast_util::outermost_paren_parent, context::LintContext, rule::Rule, AstNode};
+
+#[derive(Debug, Error, Diagnostic)]
+#[error("eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals")]
+#[diagnostic(severity(warning), help("Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback."))]
+struct NoUselessFallbackInSpreadDiagnostic(#[label] pub Span);
+
+#[derive(Debug, Default, Clone)]
+pub struct NoUselessFallbackInSpread;
+
+declare_oxc_lint!(
+    /// ### What it does
+    ///
+    /// Disallow useless fallback when spreading in object literals.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// Spreading [falsy values](https://developer.mozilla.org/en-US/docs/Glossary/Falsy) in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+    ///
+    /// ### Example
+    /// ```javascript
+    /// // bad
+    /// const object = { ...(foo || {}) }
+    ///
+    /// // good
+    /// const object = { ...foo }
+    /// const object = { ...(foo || { not: "empty" }) }
+    ///
+    /// ```
+    NoUselessFallbackInSpread,
+    correctness
+);
+
+impl Rule for NoUselessFallbackInSpread {
+    fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
+        let AstKind::LogicalExpression(logical_expression) = node.kind() else { return };
+
+        if !matches!(logical_expression.operator, LogicalOperator::Or | LogicalOperator::Coalesce) {
+            return;
+        }
+
+        let Expression::ObjectExpression(object_expression) =
+            &logical_expression.right.without_parenthesized()
+        else {
+            return;
+        };
+
+        if object_expression.properties.len() != 0 {
+            return;
+        }
+
+        let Some(parent) = outermost_paren_parent(node, ctx) else { return };
+
+        let AstKind::SpreadElement(spread_element) = parent.kind() else { return };
+
+        let Some(parent) = outermost_paren_parent(parent, ctx) else { return };
+
+        if !matches!(parent.kind(), AstKind::ObjectExpression(_)) {
+            return;
+        }
+
+        ctx.diagnostic(NoUselessFallbackInSpreadDiagnostic(spread_element.span));
+    }
+}
+
+#[test]
+fn test() {
+    use crate::tester::Tester;
+
+    let pass = vec![
+        r#"const array = [...(foo || [])]"#,
+        r#"const array = [...(foo || {})]"#,
+        r#"const array = [...(foo && {})]"#,
+        r#"const object = {...(foo && {})}"#,
+        r#"const object = {...({} || foo)}"#,
+        r#"const object = {...({} && foo)}"#,
+        r#"const object = {...({} ?? foo)}"#,
+        r#"const object = {...(foo ? foo : {})}"#,
+        r#"const object = {...foo}"#,
+        r#"const object = {...(foo ?? ({} || {}))}"#,
+        r#"const {...foo} = object"#,
+        r#"function foo({...bar}){}"#,
+        r#"const object = {...(foo || {}).toString()}"#,
+        r#"const object = {...fn(foo || {})}"#,
+        r#"const object = call({}, ...(foo || {}))"#,
+        r#"const object = {...(foo || {not: "empty"})}"#,
+        r#"const object = {...(foo || {...{}})}"#,
+    ];
+
+    let fail = vec![
+        r#"const object = {...(foo || {})}"#,
+        r#"const object = {...(foo ?? {})}"#,
+        r#"const object = {...(foo ?? (( {} )))}"#,
+        r#"const object = {...((( foo )) ?? (( {} )))}"#,
+        r#"const object = {...(( (( foo )) ?? (( {} )) ))}"#,
+        r#"async ()=> ({...((await foo) || {})})"#,
+        r#"const object = {...(0 || {})}"#,
+        r#"const object = {...((-0) || {})}"#,
+        r#"const object = {...(.0 || {})}"#,
+        r#"const object = {...(0n || {})}"#,
+        r#"const object = {...(false || {})}"#,
+        r#"const object = {...(null || {})}"#,
+        r#"const object = {...(undefined || {})}"#,
+        r#"const object = {...((a && b) || {})}"#,
+        r#"const object = {...(NaN || {})}"#,
+        r#"const object = {...("" || {})}"#,
+        r#"const object = {...([] || {})}"#,
+        r#"const object = {...({} || {})}"#,
+        r#"const object = {...(foo || {}),}"#,
+        r#"const object = {...((foo ?? {}) || {})}"#,
+        r#"const object = {...((foo && {}) || {})}"#,
+        r#"const object = {...(foo && {} || {})}"#,
+        r#"const object = {...({...(foo || {})})}"#,
+        r#"function foo(a = {...(bar || {})}){}"#,
+        r#"const object = {...(document.all || {})}"#,
+    ];
+
+    Tester::new_without_config(NoUselessFallbackInSpread::NAME, pass, fail).test_and_snapshot();
+}

crates/oxc_linter/src/rules/unicorn/throw_new_error.rs

@@ -9,7 +9,12 @@ use oxc_macros::declare_oxc_lint;
 use oxc_span::Span;
 use regex::Regex;
 
-use crate::{ast_util::outermost_paren, context::LintContext, rule::Rule, AstNode};
+use crate::{
+    ast_util::{outermost_paren, outermost_paren_parent},
+    context::LintContext,
+    rule::Rule,
+    AstNode,
+};
 
 #[derive(Debug, Error, Diagnostic)]
 #[error("eslint-plugin-unicorn(throw-new-error): Require `new` when throwing an error.")]
@@ -49,10 +54,7 @@ impl Rule for ThrowNewError {
     fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
         let AstKind::CallExpression(call_expr) = node.kind() else { return };
 
-        let Some(outermost_paren_node) = ctx.nodes().parent_node(outermost_paren(node, ctx).id())
-        else {
-            return;
-        };
+        let Some(outermost_paren_node) = outermost_paren_parent(node, ctx) else { return };
 
         let AstKind::ThrowStatement(_) = outermost_paren(outermost_paren_node, ctx).kind() else {
             return;

crates/oxc_linter/src/snapshots/no_useless_fallback_in_spread.snap

@@ -0,0 +1,180 @@
+---
+source: crates/oxc_linter/src/tester.rs
+expression: no_useless_fallback_in_spread
+---
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(foo || {})}
+   ·                 ──────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(foo ?? {})}
+   ·                 ──────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(foo ?? (( {} )))}
+   ·                 ────────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...((( foo )) ?? (( {} )))}
+   ·                 ──────────────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(( (( foo )) ?? (( {} )) ))}
+   ·                 ──────────────────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ async ()=> ({...((await foo) || {})})
+   ·              ──────────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(0 || {})}
+   ·                 ────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...((-0) || {})}
+   ·                 ───────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(.0 || {})}
+   ·                 ─────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(0n || {})}
+   ·                 ─────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(false || {})}
+   ·                 ────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(null || {})}
+   ·                 ───────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(undefined || {})}
+   ·                 ────────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...((a && b) || {})}
+   ·                 ───────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(NaN || {})}
+   ·                 ──────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...("" || {})}
+   ·                 ─────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...([] || {})}
+   ·                 ─────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...({} || {})}
+   ·                 ─────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(foo || {}),}
+   ·                 ──────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...((foo ?? {}) || {})}
+   ·                 ──────────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...((foo && {}) || {})}
+   ·                 ──────────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(foo && {} || {})}
+   ·                 ────────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...({...(foo || {})})}
+   ·                      ──────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ function foo(a = {...(bar || {})}){}
+   ·                   ──────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+  ⚠ eslint-plugin-unicorn(no-useless-fallback-in-spread): Disallow useless fallback when spreading in object literals
+   ╭─[no_useless_fallback_in_spread.tsx:1:1]
+ 1 │ const object = {...(document.all || {})}
+   ·                 ───────────────────────
+   ╰────
+  help: Spreading falsy values in object literals won't add any unexpected properties, so it's unnecessary to add an empty object as fallback.
+
+