Fix nits and add test for `unnecessary_operation`

4 files changed, 66 insertions, 26 deletions

diff --git a/clippy_lints/src/no_effect.rs b/clippy_lints/src/no_effect.rs
index a0e7dbf9ec6..5978da83199 100644
--- a/clippy_lints/src/no_effect.rs
+++ b/clippy_lints/src/no_effect.rs
@@ -92,8 +92,10 @@ fn check_no_effect(cx: &LateContext<'_>, stmt: &Stmt<'_>) -> bool {
             return false;
         }
         let expr = peel_blocks(expr);
-        // assume nontrivial oprand of `Binary` Expr can skip `check_unnecessary_operation`
-        if is_operator_overriden(cx, 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) {
@@ -162,18 +164,18 @@ fn check_no_effect(cx: &LateContext<'_>, stmt: &Stmt<'_>) -> bool {
     false
 }
 
-fn is_operator_overriden(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
-    // It's very hard or impossable to check whether overrided operator have side-effect this lint.
-    // So, this function assume user-defined operator is overrided with an side-effect.
+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 overrided, at least one operand is ADT type
+            // 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 overrided in `ExprKind::{Binary, Unary}`.
+            // use this function to check whether operator is overridden in `ExprKind::{Binary, Unary}`.
             cx.typeck_results().is_method_call(expr)
         },
         _ => false,
diff --git a/tests/ui/unnecessary_operation.fixed b/tests/ui/unnecessary_operation.fixed
index d0c0298ef4c..463412daec0 100644
--- a/tests/ui/unnecessary_operation.fixed
+++ b/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;
 }
diff --git a/tests/ui/unnecessary_operation.rs b/tests/ui/unnecessary_operation.rs
index e8e3a2d5657..f0d28e28902 100644
--- a/tests/ui/unnecessary_operation.rs
+++ b/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;
 }
diff --git a/tests/ui/unnecessary_operation.stderr b/tests/ui/unnecessary_operation.stderr
index fbe495f518f..eeee9ad6006 100644
--- a/tests/ui/unnecessary_operation.stderr
+++ b/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();`
@@ -8,103 +8,103 @@ 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()
@@ -112,7 +112,7 @@ 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"),