feat(linter): overhaul unicorn/no-useless-spread (#4791)

I got tired of seeing useless spreads on ternaries and `arr.reduce()` within my company's internal codebase so I overhauled this rule.

## Changes
- add fixer for object spreads
  ```js
  const before = { a, ...{ b, c }, d }
  const after = { a,  b, c, d } // fixer does not dedupe spaces before `b`
  ```
- recursively check for useless clones on complex expressions. This rule now catches and auto-fixes the following cases:
   ```js
  // ternaries when both branches create a new array or object
   const obj = { ...(foo ? { a: 1 } : { b: 2 }) }
  // recursive, so this can support complex cases
  const arr = [ ...(foo ? a.map(fn) : bar ? Array.from(iter) : await Promise.all(bar)) ]
  // reduce functions where the initial accumulator creates a new object or array
   const obj = { ...(arr.reduce(fn, {}) }
  ```

Author: DonIsaac

crates/oxc_linter/src/ast_util.rs

@@ -233,20 +233,10 @@ 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())
+    ctx.nodes()
+        .iter_parents(node.id())
+        .skip(1)
+        .find(|parent| !matches!(parent.kind(), AstKind::ParenthesizedExpression(_)))
 }
 
 pub fn get_declaration_of_variable<'a, 'b>(

crates/oxc_linter/src/rules/unicorn/no_useless_spread/const_eval.rs

@@ -0,0 +1,232 @@
+use oxc_ast::ast::{
+    match_expression, Argument, CallExpression, ConditionalExpression, Expression, NewExpression,
+};
+
+use crate::ast_util::{is_method_call, is_new_expression};
+
+#[derive(Debug, Clone)]
+pub(super) enum ValueHint {
+    NewObject,
+    NewArray,
+    Promise(Box<ValueHint>),
+    Unknown,
+}
+
+impl ValueHint {
+    pub fn r#await(self) -> Self {
+        match self {
+            Self::Promise(inner) => *inner,
+            _ => self,
+        }
+    }
+
+    #[inline]
+    pub fn is_object(&self) -> bool {
+        matches!(self, Self::NewObject)
+    }
+
+    #[inline]
+    pub fn is_array(&self) -> bool {
+        matches!(self, Self::NewArray)
+    }
+}
+
+impl std::ops::BitAnd for ValueHint {
+    type Output = Self;
+    fn bitand(self, rhs: Self) -> Self::Output {
+        match (self, rhs) {
+            (Self::NewArray, Self::NewArray) => Self::NewArray,
+            (Self::NewObject, Self::NewObject) => Self::NewObject,
+            _ => Self::Unknown,
+        }
+    }
+}
+pub(super) trait ConstEval {
+    fn const_eval(&self) -> ValueHint;
+}
+
+impl<'a> ConstEval for Expression<'a> {
+    fn const_eval(&self) -> ValueHint {
+        match self.get_inner_expression() {
+            Self::ArrayExpression(_) => ValueHint::NewArray,
+            Self::ObjectExpression(_) => ValueHint::NewObject,
+            Self::AwaitExpression(expr) => expr.argument.const_eval().r#await(),
+            Self::SequenceExpression(expr) => {
+                expr.expressions.last().map_or(ValueHint::Unknown, ConstEval::const_eval)
+            }
+            Self::ConditionalExpression(cond) => cond.const_eval(),
+            Self::CallExpression(call) => call.const_eval(),
+            Self::NewExpression(new) => new.const_eval(),
+            _ => ValueHint::Unknown,
+        }
+    }
+}
+
+impl<'a> ConstEval for ConditionalExpression<'a> {
+    fn const_eval(&self) -> ValueHint {
+        self.consequent.const_eval() & self.alternate.const_eval()
+    }
+}
+
+impl<'a> ConstEval for Argument<'a> {
+    fn const_eval(&self) -> ValueHint {
+        match self {
+            // using a spread as an initial accumulator value creates a new
+            // object or array
+            Self::SpreadElement(spread) => spread.argument.const_eval(),
+            expr @ match_expression!(Argument) => expr.as_expression().unwrap().const_eval(),
+        }
+    }
+}
+
+impl<'a> ConstEval for NewExpression<'a> {
+    fn const_eval(&self) -> ValueHint {
+        if is_new_array(self) || is_new_map_or_set(self) || is_new_typed_array(self) {
+            ValueHint::NewArray
+        } else if is_new_object(self) {
+            ValueHint::NewObject
+        } else {
+            ValueHint::Unknown
+        }
+    }
+}
+
+fn is_new_array(new_expr: &NewExpression) -> bool {
+    is_new_expression(new_expr, &["Array"], None, None)
+}
+
+/// Matches `new {Set,WeakSet,Map,WeakMap}(iterable?)`
+fn is_new_map_or_set(new_expr: &NewExpression) -> bool {
+    is_new_expression(new_expr, &["Map", "WeakMap", "Set", "WeakSet"], None, Some(1))
+}
+
+/// Matches `new Object()` with any number of args.
+fn is_new_object(new_expr: &NewExpression) -> bool {
+    is_new_expression(new_expr, &["Object"], None, None)
+}
+
+/// Matches `new <TypedArray>(a, [other args])` with >= 1 arg
+pub fn is_new_typed_array(new_expr: &NewExpression) -> bool {
+    is_new_expression(
+        new_expr,
+        &[
+            "Int8Array",
+            "Uint8Array",
+            "Uint8ClampedArray",
+            "Int16Array",
+            "Uint16Array",
+            "Int32Array",
+            "Uint32Array",
+            "Float32Array",
+            "Float64Array",
+            "BigInt64Array",
+            "BigUint64Array",
+        ],
+        Some(1),
+        None,
+    )
+}
+
+impl<'a> ConstEval for CallExpression<'a> {
+    fn const_eval(&self) -> ValueHint {
+        if is_array_from(self)
+            || is_split_method(self)
+            || is_array_factory(self)
+            || is_functional_array_method(self)
+            || is_array_producing_obj_method(self)
+        {
+            ValueHint::NewArray
+        } else if is_array_reduce(self) {
+            self.arguments[1].const_eval()
+        } else if is_promise_array_method(self) {
+            ValueHint::Promise(Box::new(ValueHint::NewArray))
+        } else if is_obj_factory(self) {
+            ValueHint::NewObject
+        } else {
+            // TODO: check initial value for arr.reduce() accumulators
+            ValueHint::Unknown
+        }
+    }
+}
+
+/// - `Array.from(x)`
+/// - `Int8Array.from(x)`
+/// - plus all other typed arrays
+pub fn is_array_from(call_expr: &CallExpression) -> bool {
+    is_method_call(
+        call_expr,
+        Some(&[
+            "Array",
+            "Int8Array",
+            "Uint8Array",
+            "Uint8ClampedArray",
+            "Int16Array",
+            "Uint16Array",
+            "Int32Array",
+            "Uint32Array",
+            "Float32Array",
+            "Float64Array",
+            "BigInt64Array",
+            "BigUint64Array",
+        ]),
+        Some(&["from"]),
+        Some(1),
+        Some(1),
+    )
+}
+/// `<expr>.{concat,map,filter,...}`
+fn is_functional_array_method(call_expr: &CallExpression) -> bool {
+    is_method_call(
+        call_expr,
+        None,
+        Some(&[
+            "concat",
+            "copyWithin",
+            "filter",
+            "flat",
+            "flatMap",
+            "map",
+            "slice",
+            "splice",
+            "toReversed",
+            "toSorted",
+            "toSpliced",
+            "with",
+        ]),
+        None,
+        None,
+    )
+}
+
+/// Matches `<expr>.reduce(a, b)`, which usually looks like
+/// ```ts
+/// arr.reduce(reducerRn, initialAccumulator)
+/// ```
+fn is_array_reduce(call_expr: &CallExpression) -> bool {
+    is_method_call(call_expr, None, Some(&["reduce"]), Some(2), Some(2))
+}
+
+/// Matches `<expr>.split(...)`, which usually is `String.prototype.split(pattern)`
+fn is_split_method(call_expr: &CallExpression) -> bool {
+    is_method_call(call_expr, None, Some(&["split"]), None, None)
+}
+
+/// Matches `Object.{fromEntries,create}(x)`
+fn is_obj_factory(call_expr: &CallExpression) -> bool {
+    is_method_call(call_expr, Some(&["Object"]), Some(&["fromEntries", "create"]), Some(1), Some(1))
+}
+
+/// Matches `Object.{keys,values,entries}(...)`
+fn is_array_producing_obj_method(call_expr: &CallExpression) -> bool {
+    is_method_call(call_expr, Some(&["Object"]), Some(&["keys", "values", "entries"]), None, None)
+}
+
+/// Matches `Array.{from,of}(...)`
+fn is_array_factory(call_expr: &CallExpression) -> bool {
+    is_method_call(call_expr, Some(&["Array"]), Some(&["from", "of"]), None, None)
+}
+
+/// Matches `Promise.{all,allSettled}(x)`
+fn is_promise_array_method(call_expr: &CallExpression) -> bool {
+    is_method_call(call_expr, Some(&["Promise"]), Some(&["all", "allSettled"]), Some(1), Some(1))
+}