Lint unused parentheses around method receiver

Author: chenyukang

compiler/rustc_lint/src/unused.rs

@@ -623,6 +623,7 @@ impl<'tcx> LateLintPass<'tcx> for PathStatements {
 enum UnusedDelimsCtx {
     FunctionArg,
     MethodArg,
+    MethodReceiver,
     AssignedValue,
     AssignedValueLetElse,
     IfCond,
@@ -645,6 +646,7 @@ impl From<UnusedDelimsCtx> for &'static str {
         match ctx {
             UnusedDelimsCtx::FunctionArg => "function argument",
             UnusedDelimsCtx::MethodArg => "method argument",
+            UnusedDelimsCtx::MethodReceiver => "method receiver",
             UnusedDelimsCtx::AssignedValue | UnusedDelimsCtx::AssignedValueLetElse => {
                 "assigned value"
             }
@@ -710,6 +712,18 @@ trait UnusedDelimLint {
             }
         }
 
+        // For method receivers, only lint simple path expressions like `(x).method()`.
+        // Keep parens for all other cases to avoid false positives with complex expressions
+        // like `(1..10).sum()`, `(*ptr).method()`, `({ block }).method()`, etc.
+        // Only lint simple variable names like `(x).method()`, not qualified paths like
+        // `(Float::MIN).method()` which are clearer with parentheses.
+        if ctx == UnusedDelimsCtx::MethodReceiver {
+            match &inner.kind {
+                ast::ExprKind::Path(None, path) if path.segments.len() == 1 => {}
+                _ => return true,
+            }
+        }
+
         // Check it's range in LetScrutineeExpr
         if let ast::ExprKind::Range(..) = inner.kind
             && matches!(ctx, UnusedDelimsCtx::LetScrutineeExpr)
@@ -976,13 +990,15 @@ trait UnusedDelimLint {
             }
             // either function/method call, or something this lint doesn't care about
             ref call_or_other => {
-                let (args_to_check, ctx) = match *call_or_other {
-                    Call(_, ref args) => (&args[..], UnusedDelimsCtx::FunctionArg),
-                    MethodCall(ref call) => (&call.args[..], UnusedDelimsCtx::MethodArg),
+                let (args_to_check, ctx, receiver) = match *call_or_other {
+                    Call(_, ref args) => (&args[..], UnusedDelimsCtx::FunctionArg, None),
+                    MethodCall(ref call) => {
+                        (&call.args[..], UnusedDelimsCtx::MethodArg, Some(&call.receiver))
+                    }
                     Closure(ref closure)
                         if matches!(closure.fn_decl.output, FnRetTy::Default(_)) =>
                     {
-                        (&[closure.body.clone()][..], UnusedDelimsCtx::ClosureBody)
+                        (&[closure.body.clone()][..], UnusedDelimsCtx::ClosureBody, None)
                     }
                     // actual catch-all arm
                     _ => {
@@ -999,6 +1015,17 @@ trait UnusedDelimLint {
                 for arg in args_to_check {
                     self.check_unused_delims_expr(cx, arg, ctx, false, None, None, false);
                 }
+                if let Some(recv) = receiver {
+                    self.check_unused_delims_expr(
+                        cx,
+                        recv,
+                        UnusedDelimsCtx::MethodReceiver,
+                        false,
+                        None,
+                        None,
+                        false,
+                    );
+                }
                 return;
             }
         };
@@ -1584,6 +1611,7 @@ impl UnusedDelimLint for UnusedBraces {
                 if let [stmt] = inner.stmts.as_slice()
                     && let ast::StmtKind::Expr(ref expr) = stmt.kind
                     && !Self::is_expr_delims_necessary(expr, ctx, followed_by_block)
+                    && ctx != UnusedDelimsCtx::MethodReceiver
                     && (ctx != UnusedDelimsCtx::AnonConst
                         || (matches!(expr.kind, ast::ExprKind::Lit(_))
                             && !expr.span.from_expansion()))

library/compiler-builtins/libm/src/math/cbrt.rs

@@ -194,7 +194,7 @@ pub fn cbrt_round(x: f64, round: Round) -> FpResult<f64> {
         let mut cvt4: u64 = y1.to_bits();
         cvt4 = (cvt4 + (164 << 15)) & 0xffffffffffff0000u64;
 
-        if ((f64::from_bits(cvt4) - y1) - dy).abs() < hf64!("0x1p-60") || (zz).abs() == 1.0 {
+        if ((f64::from_bits(cvt4) - y1) - dy).abs() < hf64!("0x1p-60") || zz.abs() == 1.0 {
             cvt3 = (cvt3 + (1u64 << 15)) & 0xffffffffffff0000u64;
         }
     }

library/core/src/ptr/const_ptr.rs

@@ -27,7 +27,7 @@ impl<T: PointeeSized> *const T {
             @capture { ptr: *const u8 } -> bool:
             // This use of `const_raw_ptr_comparison` has been explicitly blessed by t-lang.
             if const #[rustc_allow_const_fn_unstable(const_raw_ptr_comparison)] {
-                match (ptr).guaranteed_eq(null_mut()) {
+                match ptr.guaranteed_eq(null_mut()) {
                     Some(res) => res,
                     // To remain maximally conservative, we stop execution when we don't
                     // know whether the pointer is null or not.

src/tools/rust-analyzer/crates/hir-ty/src/consteval.rs

@@ -96,7 +96,7 @@ pub fn intern_const_ref<'a>(
                     BuiltinUint::U16 => Box::new((i as u16).to_le_bytes()),
                     BuiltinUint::U32 => Box::new((i as u32).to_le_bytes()),
                     BuiltinUint::U64 => Box::new((i as u64).to_le_bytes()),
-                    BuiltinUint::U128 => Box::new((i).to_le_bytes()),
+                    BuiltinUint::U128 => Box::new(i.to_le_bytes()),
                     BuiltinUint::Usize => Box::new((i as usize).to_le_bytes()),
                 },
                 _ => return Const::new(interner, rustc_type_ir::ConstKind::Error(ErrorGuaranteed)),
@@ -136,7 +136,7 @@ pub fn intern_const_ref<'a>(
                     BuiltinInt::I16 => Box::new((i as i16).to_le_bytes()),
                     BuiltinInt::I32 => Box::new((i as i32).to_le_bytes()),
                     BuiltinInt::I64 => Box::new((i as i64).to_le_bytes()),
-                    BuiltinInt::I128 => Box::new((i).to_le_bytes()),
+                    BuiltinInt::I128 => Box::new(i.to_le_bytes()),
                     BuiltinInt::Isize => Box::new((i as isize).to_le_bytes()),
                 },
                 _ => return Const::new(interner, rustc_type_ir::ConstKind::Error(ErrorGuaranteed)),

src/tools/rust-analyzer/crates/hir-ty/src/mir/lower/pattern_matching.rs

@@ -336,7 +336,7 @@ impl<'db> MirLowerCtx<'_, 'db> {
                         id,
                         mode,
                         next_place,
-                        (slice).into(),
+                        slice.into(),
                         current,
                         current_else,
                     )?;

src/tools/test-float-parse/src/validate.rs

@@ -71,7 +71,7 @@ impl Constants {
         let neg_inf_cutoff = -&inf_cutoff;
 
         let powers_of_two: BTreeMap<i32, _> =
-            (POWERS_OF_TWO_RANGE).map(|n| (n, two.pow(n))).collect();
+            POWERS_OF_TWO_RANGE.map(|n| (n, two.pow(n))).collect();
         let mut half_ulp = powers_of_two.clone();
         half_ulp.iter_mut().for_each(|(_k, v)| *v = &*v / two_int);
 

tests/ui/lint/unused-parens-method-receiver-issue-151985.fixed

@@ -0,0 +1,26 @@
+//@ run-rustfix
+
+#![deny(unused_parens)]
+
+struct Thing;
+impl Thing {
+    fn method(self) {}
+}
+
+fn main() {
+    // Unnecessary parens - should warn
+    let x = Thing;
+    x.method(); //~ ERROR unnecessary parentheses around method receiver
+
+    // Necessary parens - should NOT warn
+    let _ = (1..10).sum::<i32>();           // Range expression
+    let _ = (1_i32 + 2).abs();               // Binary expression
+    let _ = (-1_i32).abs();                  // Unary expression
+    let _ = (true as i32).abs();             // Cast expression
+    let _ = (&42).clone();                   // AddrOf expression
+    let _ = (&mut 42).clone();               // AddrOf mut expression
+
+    // Block expressions - should NOT warn
+    let _ = ({ 1_i32 }).abs();               // Block expression
+    let _ = (unsafe { std::mem::zeroed::<i32>() }).abs(); // Unsafe block expression
+}

tests/ui/lint/unused-parens-method-receiver-issue-151985.rs

@@ -0,0 +1,26 @@
+//@ run-rustfix
+
+#![deny(unused_parens)]
+
+struct Thing;
+impl Thing {
+    fn method(self) {}
+}
+
+fn main() {
+    // Unnecessary parens - should warn
+    let x = Thing;
+    (x).method(); //~ ERROR unnecessary parentheses around method receiver
+
+    // Necessary parens - should NOT warn
+    let _ = (1..10).sum::<i32>();           // Range expression
+    let _ = (1_i32 + 2).abs();               // Binary expression
+    let _ = (-1_i32).abs();                  // Unary expression
+    let _ = (true as i32).abs();             // Cast expression
+    let _ = (&42).clone();                   // AddrOf expression
+    let _ = (&mut 42).clone();               // AddrOf mut expression
+
+    // Block expressions - should NOT warn
+    let _ = ({ 1_i32 }).abs();               // Block expression
+    let _ = (unsafe { std::mem::zeroed::<i32>() }).abs(); // Unsafe block expression
+}

tests/ui/lint/unused-parens-method-receiver-issue-151985.stderr

@@ -0,0 +1,19 @@
+error: unnecessary parentheses around method receiver
+  --> $DIR/unused-parens-method-receiver-issue-151985.rs:13:5
+   |
+LL |     (x).method();
+   |     ^ ^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-parens-method-receiver-issue-151985.rs:3:9
+   |
+LL | #![deny(unused_parens)]
+   |         ^^^^^^^^^^^^^
+help: remove these parentheses
+   |
+LL -     (x).method();
+LL +     x.method();
+   |
+
+error: aborting due to 1 previous error
+