New Lint: Implement unnecessary_paren_in_negated_if lint

clippy_lints/src/lib.rs

@@ -72,7 +72,7 @@ pub mod ctfe; // Very important lint, do not remove (rust#125116)
 pub mod declared_lints;
 pub mod deprecated_lints;
 
-// begin lints modules, do not remove this comment, it’s used in `update_lints`
+// begin lints modules, do not remove this comment, it's used in `update_lints`
 mod absolute_paths;
 mod almost_complete_range;
 mod approx_const;
@@ -375,6 +375,7 @@ mod unnecessary_box_returns;
 mod unnecessary_literal_bound;
 mod unnecessary_map_on_constructor;
 mod unnecessary_owned_empty_strings;
+mod unnecessary_paren_in_negated_if;
 mod unnecessary_self_imports;
 mod unnecessary_semicolon;
 mod unnecessary_struct_initialization;
@@ -404,7 +405,7 @@ mod zero_div_zero;
 mod zero_repeat_side_effects;
 mod zero_sized_map_values;
 mod zombie_processes;
-// end lints modules, do not remove this comment, it’s used in `update_lints`
+// end lints modules, do not remove this comment, it's used in `update_lints`
 
 use clippy_config::{Conf, get_configuration_metadata, sanitize_explanation};
 use clippy_utils::macros::FormatArgsStorage;
@@ -616,7 +617,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
         store.register_late_pass(|_| {
             Box::<utils::internal_lints::lint_without_lint_pass::LintWithoutLintPass>::default()
         });
-        store.register_late_pass(|_| Box::<utils::internal_lints::unnecessary_def_path::UnnecessaryDefPath>::default());
+        store.register_late_pass(|_| Box::new(utils::internal_lints::unnecessary_def_path::UnnecessaryDefPath));
         store.register_late_pass(|_| Box::new(utils::internal_lints::outer_expn_data_pass::OuterExpnDataPass));
         store.register_late_pass(|_| Box::new(utils::internal_lints::msrv_attr_impl::MsrvAttrImpl));
         store.register_late_pass(|_| {
@@ -984,5 +985,5 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(move |_| Box::new(non_std_lazy_statics::NonStdLazyStatic::new(conf)));
     store.register_late_pass(|_| Box::new(manual_option_as_slice::ManualOptionAsSlice::new(conf)));
     store.register_late_pass(|_| Box::new(single_option_map::SingleOptionMap));
-    // add lints here, do not remove this comment, it's used in `new_lint`
+    store.register_lints(&[&unnecessary_paren_in_negated_if::UNNECESSARY_PAREN_IN_NEGATED_IF]);
 }

clippy_lints/src/unnecessary_paren_in_negated_if.rs

@@ -0,0 +1,68 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, UnOp};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::declare_lint_pass;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for unnecessary parentheses in negated if conditions.
+    ///
+    /// ### Why is this bad?
+    /// Unnecessary parentheses make code harder to read and add visual noise.
+    ///
+    /// ### Example
+    /// ```rust
+    /// if !(condition) {
+    ///     // ...
+    /// }
+    /// ```
+    ///
+    /// Use instead:
+    /// ```rust
+    /// if !condition {
+    ///     // ...
+    /// }
+    /// ```
+    #[clippy::version = "1.75.0"]
+    pub UNNECESSARY_PAREN_IN_NEGATED_IF,
+    style,
+    "unnecessary parentheses in negated if conditions"
+}
+
+declare_lint_pass!(UnnecessaryParenInNegatedIf => [UNNECESSARY_PAREN_IN_NEGATED_IF]);
+
+impl<'tcx> LateLintPass<'tcx> for UnnecessaryParenInNegatedIf {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        if let ExprKind::If(cond, ..) = expr.kind {
+            // Check if the condition is a negation
+            if let ExprKind::Unary(UnOp::Not, inner) = cond.kind {
+                // Check if the inner expression is parenthesized by examining the source code
+                let mut applicability = Applicability::MachineApplicable;
+                let inner_snippet = snippet_with_applicability(cx, inner.span, "..", &mut applicability);
+
+                // If the snippet starts with '(' and ends with ')', it's likely parenthesized
+                if inner_snippet.starts_with('(') && inner_snippet.ends_with(')') {
+                    // Extract the content inside the parentheses
+                    let content = &inner_snippet[1..inner_snippet.len() - 1];
+
+                    // Don't lint if the expression is from a macro
+                    if expr.span.from_expansion() {
+                        return;
+                    }
+
+                    span_lint_and_sugg(
+                        cx,
+                        UNNECESSARY_PAREN_IN_NEGATED_IF,
+                        inner.span,
+                        "unnecessary parentheses in negated if condition",
+                        "try",
+                        format!("!{content}"),
+                        applicability,
+                    );
+                }
+            }
+        }
+    }
+}

tests/ui/unnecessary_paren_in_negated_if.rs

@@ -0,0 +1,27 @@
+#![warn(clippy::unnecessary_paren_in_negated_if)]
+
+fn main() {
+    let condition = true;
+
+    // These should trigger the lint
+    if !(condition) {
+        println!("Negated condition with unnecessary parentheses");
+    }
+
+    if !(condition) {
+        println!("Negated condition with double unnecessary parentheses");
+    }
+
+    // These should not trigger the lint
+    if !condition {
+        println!("Negated condition without parentheses");
+    }
+
+    if !(condition && true) {
+        println!("Negated condition with necessary parentheses");
+    }
+
+    if !(condition || false) {
+        println!("Another negated condition with necessary parentheses");
+    }
+}

tests/ui/unnecessary_paren_in_negated_if.stderr

@@ -0,0 +1,15 @@
+error: unnecessary parentheses in negated if condition
+  --> $DIR/unnecessary_paren_in_negated_if.rs:7:8
+   |
+7  |     if !(condition) {
+   |        ^^^^^^^^^^^^ help: try: `!condition`
+   |
+   = note: `-D clippy::unnecessary-paren-in-negated-if` implied by `-D warnings`
+
+error: unnecessary parentheses in negated if condition
+  --> $DIR/unnecessary_paren_in_negated_if.rs:11:8
+   |
+11 |     if !((condition)) {
+   |        ^^^^^^^^^^^^^ help: try: `!condition`
+
+error: aborting due to 2 previous errors