feat(linter) oxc: only used in recursion

crates/oxc_linter/src/rules.rs

@@ -254,6 +254,7 @@ mod oxc {
     pub mod double_comparisons;
     pub mod misrefactored_assign_op;
     pub mod no_accumulating_spread;
+    pub mod only_used_in_recursion;
 }
 
 oxc_macros::declare_all_lint_rules! {
@@ -480,4 +481,5 @@ oxc_macros::declare_all_lint_rules! {
     oxc::double_comparisons,
     oxc::misrefactored_assign_op,
     oxc::no_accumulating_spread,
+    oxc::only_used_in_recursion,
 }

crates/oxc_linter/src/rules/oxc/only_used_in_recursion.rs

@@ -0,0 +1,277 @@
+use oxc_ast::{
+    ast::{BindingIdentifier, BindingPatternKind, Expression},
+    AstKind,
+};
+use oxc_diagnostics::{
+    miette::{self, Diagnostic},
+    thiserror::{self, Error},
+};
+use oxc_macros::declare_oxc_lint;
+use oxc_span::{Atom, GetSpan, Span};
+
+use crate::{context::LintContext, rule::Rule, AstNode};
+
+#[derive(Debug, Error, Diagnostic)]
+#[error("oxc(only-used-in-recursion): Parameter `{1}` is only used in recursive calls")]
+#[diagnostic(
+    severity(warning),
+    help(
+        "Remove the argument and its usage. Alternatively, use the argument in the function body."
+    )
+)]
+struct OnlyUsedInRecursionDiagnostic(#[label] pub Span, pub Atom);
+
+#[derive(Debug, Default, Clone)]
+pub struct OnlyUsedInRecursion;
+
+declare_oxc_lint!(
+    /// ### What it does
+    ///
+    /// Checks for arguments that are only used in recursion with no side-effects.
+    ///
+    /// Inspired by https://rust-lang.github.io/rust-clippy/master/#/only_used_in_recursion
+    ///
+    /// ### Why is this bad?
+    ///
+    /// Supplying an argument that is only used in recursive calls is likely a mistake.
+    ///
+    /// It increase cognitive complexity and may impact performance.
+    ///
+    /// ### Example
+    /// ```javascript
+    /// // Bad - the argument `b` is only used in recursive calls
+    /// function f(a: number, b: number): number {
+    ///     if a == 0 {
+    ///         return 1
+    ///     } else {
+    ///         return f(a - 1, b + 1)
+    ///     }
+    /// }
+    ///
+    /// // Good - the argument `b` is omitted
+    /// function f(a: number): number {
+    ///    if a == 0 {
+    ///        return 1
+    ///    } else {
+    ///        return f(a - 1)
+    ///    }
+    /// }
+    /// ```
+    OnlyUsedInRecursion,
+    correctness
+);
+
+impl Rule for OnlyUsedInRecursion {
+    fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
+        let AstKind::Function(function) = node.kind() else { return };
+
+        let Some(function_id) = &function.id else { return };
+
+        if function.body.is_none() {
+            return;
+        }
+
+        if is_function_maybe_reassigned(function_id, ctx) {
+            return;
+        }
+
+        for (arg_index, arg) in function.params.items.iter().enumerate() {
+            let BindingPatternKind::BindingIdentifier(arg) = &arg.pattern.kind else { continue };
+
+            if is_argument_only_used_in_recursion(function_id, arg, arg_index, ctx) {
+                ctx.diagnostic(OnlyUsedInRecursionDiagnostic(arg.span, arg.name.clone()));
+            }
+        }
+    }
+}
+
+fn is_argument_only_used_in_recursion<'a>(
+    function_id: &'a BindingIdentifier,
+    arg: &'a BindingIdentifier,
+    arg_index: usize,
+    ctx: &'a LintContext<'_>,
+) -> bool {
+    let mut is_used_only_in_recursion = true;
+    let mut has_references = false;
+
+    for reference in
+        ctx.semantic().symbol_references(arg.symbol_id.get().expect("`symbol_id` should be set"))
+    {
+        has_references = true;
+        if let Some(AstKind::Argument(argument)) = ctx.nodes().parent_kind(reference.node_id()) {
+            if let Some(AstKind::CallExpression(call_expr)) =
+                ctx.nodes().parent_kind(ctx.nodes().parent_node(reference.node_id()).unwrap().id())
+            {
+                if !call_expr.arguments.iter().enumerate().any(|(index, arg)| {
+                    index == arg_index
+                        && arg.span() == argument.span()
+                        && if let Expression::Identifier(identifier) = &call_expr.callee {
+                            identifier.name == function_id.name
+                        } else {
+                            false
+                        }
+                }) {
+                    is_used_only_in_recursion = false;
+                    break;
+                }
+            } else {
+                is_used_only_in_recursion = false;
+                break;
+            }
+        } else {
+            is_used_only_in_recursion = false;
+            break;
+        }
+    }
+
+    has_references && is_used_only_in_recursion
+}
+
+fn is_function_maybe_reassigned<'a>(
+    function_id: &'a BindingIdentifier,
+    ctx: &'a LintContext<'_>,
+) -> bool {
+    let mut is_maybe_reassigned = false;
+
+    for reference in ctx
+        .semantic()
+        .symbol_references(function_id.symbol_id.get().expect("`symbol_id` should be set"))
+    {
+        if let Some(AstKind::SimpleAssignmentTarget(_)) =
+            ctx.nodes().parent_kind(reference.node_id())
+        {
+            is_maybe_reassigned = true;
+        }
+    }
+
+    is_maybe_reassigned
+}
+
+#[test]
+fn test() {
+    use crate::tester::Tester;
+
+    let pass = vec![
+        // no args, no recursion
+        "
+            function test() {
+                // some code
+            }
+        ",
+        // unused arg, no recursion
+        "
+            function test(arg0) {
+                // arg0 not used
+            }
+        ",
+        "
+            function test(arg0) {
+                anotherTest(arg0);
+            }
+
+            function anotherTest(arg) { }
+        ",
+        // conditional recursion
+        "
+            function test(arg0) {
+                if (arg0 > 0) {
+                    test(arg0 - 1);
+                }
+            }
+        ",
+        "
+            function test(arg0, arg1) {
+                // only arg0 used in recursion
+                arg0
+                test(arg0);
+            }
+        ",
+        // allowed case
+        "
+            function test() {
+                test()
+            }
+        ",
+        // arg not passed to recursive call
+        "
+            function test(arg0) {
+                arg0()
+            }
+        ",
+        "function test(arg0) { }",
+        // args in wrong order
+        "
+            function test(arg0, arg1) {
+                test(arg1, arg0)
+            }
+        ",
+        // Arguments Swapped in Recursion
+        r"
+            function test(arg0, arg1) {
+                test(arg1, arg0);
+            }
+        ",
+        // https://github.com/swc-project/swc/blob/3ca954b9f9622ed400308f2af35242583a4bdc3d/crates/swc_ecma_transforms_base/src/helpers/_get.js#L1-L16
+        r#"
+        function _get(target, property, receiver) {
+            if (typeof Reflect !== "undefined" && Reflect.get) {
+                _get = Reflect.get;
+            } else {
+                _get = function get(target, property, receiver) {
+                    var base = _super_prop_base(target, property);
+                    if (!base) return;
+                    var desc = Object.getOwnPropertyDescriptor(base, property);
+                    if (desc.get) {
+                        return desc.get.call(receiver || target);
+                    }
+                    return desc.value;
+                };
+            }
+            return _get(target, property, receiver || target);
+        }
+        "#,
+    ];
+
+    let fail = vec![
+        "
+            function test(arg0) {
+                return test(arg0);
+            }
+        ",
+        r#"
+            function test(arg0, arg1) {
+                return test("", arg1);
+            }
+        "#,
+        // Argument Not Altered in Recursion
+        r"
+            function test(arg0) {
+                test(arg0);
+            }
+        ",
+        // Wrong Number of Arguments in Recursion
+        r"
+            function test(arg0, arg1) {
+                test(arg0);
+            }
+        ",
+        // Unused Argument in Recursion
+        r"
+            function test(arg0, arg1) {
+                test(arg0);
+            }
+        ",
+        r"
+            module.exports = function test(a) {
+                test(a)
+            }
+        ",
+        r"
+            export function test(a) {
+                test(a)
+            }
+        ",
+    ];
+
+    Tester::new_without_config(OnlyUsedInRecursion::NAME, pass, fail).test_and_snapshot();
+}

crates/oxc_linter/src/snapshots/only_used_in_recursion.snap

@@ -0,0 +1,68 @@
+---
+source: crates/oxc_linter/src/tester.rs
+expression: only_used_in_recursion
+---
+  ⚠ oxc(only-used-in-recursion): Parameter `arg0` is only used in recursive calls
+   ╭─[only_used_in_recursion.tsx:1:1]
+ 1 │ 
+ 2 │             function test(arg0) {
+   ·                           ────
+ 3 │                 return test(arg0);
+   ╰────
+  help: Remove the argument and its usage. Alternatively, use the argument in the function body.
+
+  ⚠ oxc(only-used-in-recursion): Parameter `arg1` is only used in recursive calls
+   ╭─[only_used_in_recursion.tsx:1:1]
+ 1 │ 
+ 2 │             function test(arg0, arg1) {
+   ·                                 ────
+ 3 │                 return test("", arg1);
+   ╰────
+  help: Remove the argument and its usage. Alternatively, use the argument in the function body.
+
+  ⚠ oxc(only-used-in-recursion): Parameter `arg0` is only used in recursive calls
+   ╭─[only_used_in_recursion.tsx:1:1]
+ 1 │ 
+ 2 │             function test(arg0) {
+   ·                           ────
+ 3 │                 test(arg0);
+   ╰────
+  help: Remove the argument and its usage. Alternatively, use the argument in the function body.
+
+  ⚠ oxc(only-used-in-recursion): Parameter `arg0` is only used in recursive calls
+   ╭─[only_used_in_recursion.tsx:1:1]
+ 1 │ 
+ 2 │             function test(arg0, arg1) {
+   ·                           ────
+ 3 │                 test(arg0);
+   ╰────
+  help: Remove the argument and its usage. Alternatively, use the argument in the function body.
+
+  ⚠ oxc(only-used-in-recursion): Parameter `arg0` is only used in recursive calls
+   ╭─[only_used_in_recursion.tsx:1:1]
+ 1 │ 
+ 2 │             function test(arg0, arg1) {
+   ·                           ────
+ 3 │                 test(arg0);
+   ╰────
+  help: Remove the argument and its usage. Alternatively, use the argument in the function body.
+
+  ⚠ oxc(only-used-in-recursion): Parameter `a` is only used in recursive calls
+   ╭─[only_used_in_recursion.tsx:1:1]
+ 1 │ 
+ 2 │             module.exports = function test(a) {
+   ·                                            ─
+ 3 │                 test(a)
+   ╰────
+  help: Remove the argument and its usage. Alternatively, use the argument in the function body.
+
+  ⚠ oxc(only-used-in-recursion): Parameter `a` is only used in recursive calls
+   ╭─[only_used_in_recursion.tsx:1:1]
+ 1 │ 
+ 2 │             export function test(a) {
+   ·                                  ─
+ 3 │                 test(a)
+   ╰────
+  help: Remove the argument and its usage. Alternatively, use the argument in the function body.
+
+