Don't shadow unnecessary operation lint if no_effect is allowed

clippy_lints/src/no_effect.rs

@@ -1,4 +1,5 @@
 use clippy_utils::diagnostics::{span_lint_hir, span_lint_hir_and_then};
+use clippy_utils::is_lint_allowed;
 use clippy_utils::source::snippet_opt;
 use clippy_utils::ty::has_drop;
 use rustc_errors::Applicability;
@@ -79,12 +80,13 @@ impl<'tcx> LateLintPass<'tcx> for NoEffect {
 
 fn check_no_effect(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> bool {
     if let StmtKind::Semi(expr) = stmt.kind {
-        if has_no_effect(cx, expr) {
+        if has_no_effect(cx, expr) && !is_lint_allowed(cx, NO_EFFECT, expr.hir_id) {
             span_lint_hir(cx, NO_EFFECT, expr.hir_id, stmt.span, "statement with no effect");
             return true;
         }
     } else if let StmtKind::Local(local) = stmt.kind {
         if_chain! {
+            if !is_lint_allowed(cx, NO_EFFECT_UNDERSCORE_BINDING, local.hir_id);
             if let Some(init) = local.init;
             if !local.pat.span.from_expansion();
             if has_no_effect(cx, init);

tests/ui-internal/if_chain_style.stderr

@@ -32,6 +32,14 @@ error: `let` expression should be inside `then { .. }`
 LL |         let x = "";
    |         ^^^^^^^^^^^
 
+error: unnecessary operation
+  --> $DIR/if_chain_style.rs:26:13
+   |
+LL |             ();
+   |             ^^^ help: statement can be reduced to
+   |
+   = note: `-D clippy::unnecessary-operation` implied by `-D warnings`
+
 error: this `if` can be part of the outer `if_chain!`
   --> $DIR/if_chain_style.rs:35:13
    |
@@ -81,5 +89,23 @@ LL | /             let x = "";
 LL | |             let x = "";
    | |_______________________^
 
-error: aborting due to 7 previous errors
+error: unnecessary operation
+  --> $DIR/if_chain_style.rs:57:9
+   |
+LL |         ();
+   |         ^^^ help: statement can be reduced to
+
+error: unnecessary operation
+  --> $DIR/if_chain_style.rs:61:20
+   |
+LL |             then { (); }
+   |                    ^^^ help: statement can be reduced to
+
+error: unnecessary operation
+  --> $DIR/if_chain_style.rs:68:16
+   |
+LL |         then { (); }
+   |                ^^^ help: statement can be reduced to
+
+error: aborting due to 11 previous errors
 

tests/ui/author/blocks.rs

@@ -1,4 +1,4 @@
-#![allow(redundant_semicolons, clippy::no_effect)]
+#![allow(redundant_semicolons, clippy::no_effect, clippy::unnecessary_operation)]
 
 #[rustfmt::skip]
 fn main() {

tests/ui/cfg_attr_rustfmt.fixed

@@ -1,7 +1,7 @@
 // run-rustfix
 #![feature(stmt_expr_attributes)]
 
-#![allow(unused, clippy::no_effect)]
+#![allow(unused, clippy::no_effect, clippy::unnecessary_operation)]
 #![warn(clippy::deprecated_cfg_attr)]
 
 // This doesn't get linted, see known problems

tests/ui/cfg_attr_rustfmt.rs

@@ -1,7 +1,7 @@
 // run-rustfix
 #![feature(stmt_expr_attributes)]
 
-#![allow(unused, clippy::no_effect)]
+#![allow(unused, clippy::no_effect, clippy::unnecessary_operation)]
 #![warn(clippy::deprecated_cfg_attr)]
 
 // This doesn't get linted, see known problems

tests/ui/crashes/ice-7340.rs

@@ -1,4 +1,4 @@
-#![allow(clippy::no_effect)]
+#![allow(clippy::no_effect, clippy::unnecessary_operation)]
 
 fn main() {
     const CONSTANT: usize = 8;

tests/ui/erasing_op.stderr

@@ -1,3 +1,11 @@
+error: unnecessary operation
+  --> $DIR/erasing_op.rs:6:5
+   |
+LL |     x * 0;
+   |     ^^^^^^ help: statement can be reduced to: `x;0;`
+   |
+   = note: `-D clippy::unnecessary-operation` implied by `-D warnings`
+
 error: this operation will always return zero. This is likely not the intended outcome
   --> $DIR/erasing_op.rs:6:5
    |
@@ -6,17 +14,29 @@ LL |     x * 0;
    |
    = note: `-D clippy::erasing-op` implied by `-D warnings`
 
+error: unnecessary operation
+  --> $DIR/erasing_op.rs:7:5
+   |
+LL |     0 & x;
+   |     ^^^^^^ help: statement can be reduced to: `0;x;`
+
 error: this operation will always return zero. This is likely not the intended outcome
   --> $DIR/erasing_op.rs:7:5
    |
 LL |     0 & x;
    |     ^^^^^
 
+error: unnecessary operation
+  --> $DIR/erasing_op.rs:8:5
+   |
+LL |     0 / x;
+   |     ^^^^^^ help: statement can be reduced to: `0;x;`
+
 error: this operation will always return zero. This is likely not the intended outcome
   --> $DIR/erasing_op.rs:8:5
    |
 LL |     0 / x;
    |     ^^^^^
 
-error: aborting due to 3 previous errors
+error: aborting due to 6 previous errors
 

tests/ui/eta.fixed

@@ -29,7 +29,7 @@ macro_rules! closure_mac {
 
 fn main() {
     let a = Some(1u8).map(foo);
-    let c = Some(1u8).map(|a| {1+2; foo}(a));
+    let c = Some(1u8).map(|a| {1;2; foo}(a));
     true.then(|| mac!()); // don't lint function in macro expansion
     Some(1).map(closure_mac!()); // don't lint closure in macro expansion
     let _: Option<Vec<u8>> = true.then(std::vec::Vec::new); // special case vec!

tests/ui/eta.stderr

@@ -6,6 +6,14 @@ LL |     let a = Some(1u8).map(|a| foo(a));
    |
    = note: `-D clippy::redundant-closure` implied by `-D warnings`
 
+error: unnecessary operation
+  --> $DIR/eta.rs:32:32
+   |
+LL |     let c = Some(1u8).map(|a| {1+2; foo}(a));
+   |                                ^^^^ help: statement can be reduced to: `1;2;`
+   |
+   = note: `-D clippy::unnecessary-operation` implied by `-D warnings`
+
 error: redundant closure
   --> $DIR/eta.rs:35:40
    |
@@ -130,5 +138,5 @@ error: redundant closure
 LL |     map_str_to_path(|s| s.as_ref());
    |                     ^^^^^^^^^^^^^^ help: replace the closure with the method itself: `std::convert::AsRef::as_ref`
 
-error: aborting due to 21 previous errors
+error: aborting due to 22 previous errors
 

tests/ui/if_same_then_else.stderr

@@ -25,6 +25,92 @@ LL | |         foo();
 LL | |     }
    | |_____^
 
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:22:9
+   |
+LL |         Foo { bar: 42 };
+   |         ^^^^^^^^^^^^^^^^ help: statement can be reduced to: `42;`
+   |
+   = note: `-D clippy::unnecessary-operation` implied by `-D warnings`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:23:9
+   |
+LL |         0..10;
+   |         ^^^^^^ help: statement can be reduced to: `0;10;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:24:9
+   |
+LL |         ..;
+   |         ^^^ help: statement can be reduced to
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:25:9
+   |
+LL |         0..;
+   |         ^^^^ help: statement can be reduced to: `0;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:26:9
+   |
+LL |         ..10;
+   |         ^^^^^ help: statement can be reduced to: `10;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:31:9
+   |
+LL |         Foo { bar: 42 };
+   |         ^^^^^^^^^^^^^^^^ help: statement can be reduced to: `42;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:32:9
+   |
+LL |         0..10;
+   |         ^^^^^^ help: statement can be reduced to: `0;10;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:33:9
+   |
+LL |         ..;
+   |         ^^^ help: statement can be reduced to
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:34:9
+   |
+LL |         0..;
+   |         ^^^^ help: statement can be reduced to: `0;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:35:9
+   |
+LL |         ..10;
+   |         ^^^^^ help: statement can be reduced to: `10;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:41:9
+   |
+LL |         Foo { bar: 42 };
+   |         ^^^^^^^^^^^^^^^^ help: statement can be reduced to: `42;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:43:9
+   |
+LL |         Foo { bar: 43 };
+   |         ^^^^^^^^^^^^^^^^ help: statement can be reduced to: `43;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:47:9
+   |
+LL |         ();
+   |         ^^^ help: statement can be reduced to
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:53:9
+   |
+LL |         0..10;
+   |         ^^^^^^ help: statement can be reduced to: `0;10;`
+
 error: this `if` has identical blocks
   --> $DIR/if_same_then_else.rs:65:21
    |
@@ -108,5 +194,17 @@ LL | |         bar + 1;
 LL | |     }
    | |_____^
 
-error: aborting due to 5 previous errors
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:101:9
+   |
+LL |         bar + 1;
+   |         ^^^^^^^^ help: statement can be reduced to: `bar;1;`
+
+error: unnecessary operation
+  --> $DIR/if_same_then_else.rs:109:9
+   |
+LL |         bar + 1;
+   |         ^^^^^^^^ help: statement can be reduced to: `bar;1;`
+
+error: aborting due to 21 previous errors
 

tests/ui/let_unit.fixed

@@ -1,7 +1,7 @@
 // run-rustfix
 
 #![warn(clippy::let_unit_value)]
-#![allow(clippy::no_effect)]
+#![allow(clippy::no_effect, clippy::unnecessary_operation)]
 #![allow(unused_variables)]
 
 macro_rules! let_and_return {

tests/ui/let_unit.rs

@@ -1,7 +1,7 @@
 // run-rustfix
 
 #![warn(clippy::let_unit_value)]
-#![allow(clippy::no_effect)]
+#![allow(clippy::no_effect, clippy::unnecessary_operation)]
 #![allow(unused_variables)]
 
 macro_rules! let_and_return {

tests/ui/needless_bool/fixable.fixed

@@ -5,6 +5,7 @@
     unused,
     dead_code,
     clippy::no_effect,
+    clippy::unnecessary_operation,
     clippy::if_same_then_else,
     clippy::equatable_if_let,
     clippy::needless_return,

tests/ui/needless_bool/fixable.rs

@@ -5,6 +5,7 @@
     unused,
     dead_code,
     clippy::no_effect,
+    clippy::unnecessary_operation,
     clippy::if_same_then_else,
     clippy::equatable_if_let,
     clippy::needless_return,