Add a function to check whether binary oprands are nontrivial

clippy_lints/src/no_effect.rs

@@ -87,6 +87,17 @@ impl<'tcx> LateLintPass<'tcx> for NoEffect {
 
 fn check_no_effect(cx: &LateContext<'_>, stmt: &Stmt<'_>) -> bool {
     if let StmtKind::Semi(expr) = stmt.kind {
+        // move `expr.span.from_expansion()` ahead
+        if expr.span.from_expansion() {
+            return false;
+        }
+        let expr = peel_blocks(expr);
+
+        if is_operator_overridden(cx, expr) {
+            // Return `true`, to prevent `check_unnecessary_operation` from
+            // linting on this statement as well.
+            return true;
+        }
         if has_no_effect(cx, expr) {
             span_lint_hir_and_then(
                 cx,
@@ -153,11 +164,26 @@ fn check_no_effect(cx: &LateContext<'_>, stmt: &Stmt<'_>) -> bool {
     false
 }
 
-fn has_no_effect(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
-    if expr.span.from_expansion() {
-        return false;
+fn is_operator_overridden(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    // It's very hard or impossable to check whether overridden operator have side-effect this lint.
+    // So, this function assume user-defined operator is overridden with an side-effect.
+    // The definition of user-defined structure here is ADT-type,
+    // Althrough this will weaken the ability of this lint, less error lint-fix happen.
+    match expr.kind {
+        ExprKind::Binary(..) | ExprKind::Unary(..) => {
+            // No need to check type of `lhs` and `rhs`
+            // because if the operator is overridden, at least one operand is ADT type
+
+            // reference: rust/compiler/rustc_middle/src/ty/typeck_results.rs: `is_method_call`.
+            // use this function to check whether operator is overridden in `ExprKind::{Binary, Unary}`.
+            cx.typeck_results().is_method_call(expr)
+        },
+        _ => false,
     }
-    match peel_blocks(expr).kind {
+}
+
+fn has_no_effect(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    match expr.kind {
         ExprKind::Lit(..) | ExprKind::Closure { .. } => true,
         ExprKind::Path(..) => !has_drop(cx, cx.typeck_results().expr_ty(expr)),
         ExprKind::Index(a, b, _) | ExprKind::Binary(_, a, b) => has_no_effect(cx, a) && has_no_effect(cx, b),

tests/ui/no_effect.rs

@@ -9,6 +9,30 @@
     clippy::useless_vec
 )]
 
+use std::fmt::Display;
+use std::ops::{Neg, Shl};
+
+struct Cout;
+
+impl<T> Shl<T> for Cout
+where
+    T: Display,
+{
+    type Output = Self;
+    fn shl(self, rhs: T) -> Self::Output {
+        println!("{}", rhs);
+        self
+    }
+}
+
+impl Neg for Cout {
+    type Output = Self;
+    fn neg(self) -> Self::Output {
+        println!("hello world");
+        self
+    }
+}
+
 struct Unit;
 struct Tuple(i32);
 struct Struct {
@@ -174,4 +198,11 @@ fn main() {
     GreetStruct1("world");
     GreetStruct2()("world");
     GreetStruct3 {}("world");
+
+    fn n() -> i32 {
+        42
+    }
+
+    Cout << 142;
+    -Cout;
 }

tests/ui/no_effect.stderr

@@ -1,5 +1,5 @@
 error: statement with no effect
-  --> $DIR/no_effect.rs:98:5
+  --> $DIR/no_effect.rs:122:5
    |
 LL |     0;
    |     ^^
@@ -8,151 +8,151 @@ LL |     0;
    = help: to override `-D warnings` add `#[allow(clippy::no_effect)]`
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:101:5
+  --> $DIR/no_effect.rs:125:5
    |
 LL |     s2;
    |     ^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:103:5
+  --> $DIR/no_effect.rs:127:5
    |
 LL |     Unit;
    |     ^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:105:5
+  --> $DIR/no_effect.rs:129:5
    |
 LL |     Tuple(0);
    |     ^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:107:5
+  --> $DIR/no_effect.rs:131:5
    |
 LL |     Struct { field: 0 };
    |     ^^^^^^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:109:5
+  --> $DIR/no_effect.rs:133:5
    |
 LL |     Struct { ..s };
    |     ^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:111:5
+  --> $DIR/no_effect.rs:135:5
    |
 LL |     Union { a: 0 };
    |     ^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:113:5
+  --> $DIR/no_effect.rs:137:5
    |
 LL |     Enum::Tuple(0);
    |     ^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:115:5
+  --> $DIR/no_effect.rs:139:5
    |
 LL |     Enum::Struct { field: 0 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:117:5
+  --> $DIR/no_effect.rs:141:5
    |
 LL |     5 + 6;
    |     ^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:119:5
+  --> $DIR/no_effect.rs:143:5
    |
 LL |     *&42;
    |     ^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:121:5
+  --> $DIR/no_effect.rs:145:5
    |
 LL |     &6;
    |     ^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:123:5
+  --> $DIR/no_effect.rs:147:5
    |
 LL |     (5, 6, 7);
    |     ^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:125:5
+  --> $DIR/no_effect.rs:149:5
    |
 LL |     ..;
    |     ^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:127:5
+  --> $DIR/no_effect.rs:151:5
    |
 LL |     5..;
    |     ^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:129:5
+  --> $DIR/no_effect.rs:153:5
    |
 LL |     ..5;
    |     ^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:131:5
+  --> $DIR/no_effect.rs:155:5
    |
 LL |     5..6;
    |     ^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:133:5
+  --> $DIR/no_effect.rs:157:5
    |
 LL |     5..=6;
    |     ^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:135:5
+  --> $DIR/no_effect.rs:159:5
    |
 LL |     [42, 55];
    |     ^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:137:5
+  --> $DIR/no_effect.rs:161:5
    |
 LL |     [42, 55][1];
    |     ^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:139:5
+  --> $DIR/no_effect.rs:163:5
    |
 LL |     (42, 55).1;
    |     ^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:141:5
+  --> $DIR/no_effect.rs:165:5
    |
 LL |     [42; 55];
    |     ^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:143:5
+  --> $DIR/no_effect.rs:167:5
    |
 LL |     [42; 55][13];
    |     ^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:146:5
+  --> $DIR/no_effect.rs:170:5
    |
 LL |     || x += 5;
    |     ^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:149:5
+  --> $DIR/no_effect.rs:173:5
    |
 LL |     FooString { s: s };
    |     ^^^^^^^^^^^^^^^^^^^
 
 error: binding to `_` prefixed variable with no side-effect
-  --> $DIR/no_effect.rs:151:5
+  --> $DIR/no_effect.rs:175:5
    |
 LL |     let _unused = 1;
    |     ^^^^^^^^^^^^^^^^
@@ -161,19 +161,19 @@ LL |     let _unused = 1;
    = help: to override `-D warnings` add `#[allow(clippy::no_effect_underscore_binding)]`
 
 error: binding to `_` prefixed variable with no side-effect
-  --> $DIR/no_effect.rs:154:5
+  --> $DIR/no_effect.rs:178:5
    |
 LL |     let _penguin = || println!("Some helpful closure");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: binding to `_` prefixed variable with no side-effect
-  --> $DIR/no_effect.rs:156:5
+  --> $DIR/no_effect.rs:180:5
    |
 LL |     let _duck = Struct { field: 0 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: binding to `_` prefixed variable with no side-effect
-  --> $DIR/no_effect.rs:158:5
+  --> $DIR/no_effect.rs:182:5
    |
 LL |     let _cat = [2, 4, 6, 8][2];
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^

tests/ui/unnecessary_operation.fixed

@@ -7,6 +7,9 @@
 )]
 #![warn(clippy::unnecessary_operation)]
 
+use std::fmt::Display;
+use std::ops::Shl;
+
 struct Tuple(i32);
 struct Struct {
     field: i32,
@@ -50,6 +53,19 @@ fn get_drop_struct() -> DropStruct {
     DropStruct { field: 0 }
 }
 
+struct Cout;
+
+impl<T> Shl<T> for Cout
+where
+    T: Display,
+{
+    type Output = Self;
+    fn shl(self, rhs: T) -> Self::Output {
+        println!("{}", rhs);
+        self
+    }
+}
+
 fn main() {
     get_number();
     get_number();
@@ -87,4 +103,7 @@ fn main() {
         ($($e:expr),*) => {{ $($e;)* }}
     }
     use_expr!(isize::MIN / -(one() as isize), i8::MIN / -one());
+
+    // Issue #11885
+    Cout << 16;
 }

tests/ui/unnecessary_operation.rs

@@ -7,6 +7,9 @@
 )]
 #![warn(clippy::unnecessary_operation)]
 
+use std::fmt::Display;
+use std::ops::Shl;
+
 struct Tuple(i32);
 struct Struct {
     field: i32,
@@ -50,6 +53,19 @@ fn get_drop_struct() -> DropStruct {
     DropStruct { field: 0 }
 }
 
+struct Cout;
+
+impl<T> Shl<T> for Cout
+where
+    T: Display,
+{
+    type Output = Self;
+    fn shl(self, rhs: T) -> Self::Output {
+        println!("{}", rhs);
+        self
+    }
+}
+
 fn main() {
     Tuple(get_number());
     Struct { field: get_number() };
@@ -91,4 +107,7 @@ fn main() {
         ($($e:expr),*) => {{ $($e;)* }}
     }
     use_expr!(isize::MIN / -(one() as isize), i8::MIN / -one());
+
+    // Issue #11885
+    Cout << 16;
 }

tests/ui/unnecessary_operation.stderr

@@ -1,5 +1,5 @@
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:54:5
+  --> $DIR/unnecessary_operation.rs:70:5
    |
 LL |     Tuple(get_number());
    |     ^^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
@@ -8,111 +8,111 @@ LL |     Tuple(get_number());
    = help: to override `-D warnings` add `#[allow(clippy::unnecessary_operation)]`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:55:5
+  --> $DIR/unnecessary_operation.rs:71:5
    |
 LL |     Struct { field: get_number() };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:56:5
+  --> $DIR/unnecessary_operation.rs:72:5
    |
 LL |     Struct { ..get_struct() };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_struct();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:57:5
+  --> $DIR/unnecessary_operation.rs:73:5
    |
 LL |     Enum::Tuple(get_number());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:58:5
+  --> $DIR/unnecessary_operation.rs:74:5
    |
 LL |     Enum::Struct { field: get_number() };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:59:5
+  --> $DIR/unnecessary_operation.rs:75:5
    |
 LL |     5 + get_number();
    |     ^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `5;get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:60:5
+  --> $DIR/unnecessary_operation.rs:76:5
    |
 LL |     *&get_number();
    |     ^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:61:5
+  --> $DIR/unnecessary_operation.rs:77:5
    |
 LL |     &get_number();
    |     ^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:62:5
+  --> $DIR/unnecessary_operation.rs:78:5
    |
 LL |     (5, 6, get_number());
    |     ^^^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `5;6;get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:63:5
+  --> $DIR/unnecessary_operation.rs:79:5
    |
 LL |     get_number()..;
    |     ^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:64:5
+  --> $DIR/unnecessary_operation.rs:80:5
    |
 LL |     ..get_number();
    |     ^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:65:5
+  --> $DIR/unnecessary_operation.rs:81:5
    |
 LL |     5..get_number();
    |     ^^^^^^^^^^^^^^^^ help: statement can be reduced to: `5;get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:66:5
+  --> $DIR/unnecessary_operation.rs:82:5
    |
 LL |     [42, get_number()];
    |     ^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `42;get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:67:5
+  --> $DIR/unnecessary_operation.rs:83:5
    |
 LL |     [42, 55][get_usize()];
    |     ^^^^^^^^^^^^^^^^^^^^^^ help: statement can be written as: `assert!([42, 55].len() > get_usize());`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:68:5
+  --> $DIR/unnecessary_operation.rs:84:5
    |
 LL |     (42, get_number()).1;
    |     ^^^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `42;get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:69:5
+  --> $DIR/unnecessary_operation.rs:85:5
    |
 LL |     [get_number(); 55];
    |     ^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:70:5
+  --> $DIR/unnecessary_operation.rs:86:5
    |
 LL |     [42; 55][get_usize()];
    |     ^^^^^^^^^^^^^^^^^^^^^^ help: statement can be written as: `assert!([42; 55].len() > get_usize());`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:71:5
+  --> $DIR/unnecessary_operation.rs:87:5
    |
 LL | /     {
 LL | |         get_number()
 LL | |     };
    | |______^ help: statement can be reduced to: `get_number();`
 
 error: unnecessary operation
-  --> $DIR/unnecessary_operation.rs:74:5
+  --> $DIR/unnecessary_operation.rs:90:5
    |
 LL | /     FooString {
 LL | |         s: String::from("blah"),