From fc8ab099c38952b91e38608c386314bde6dd2629 Mon Sep 17 00:00:00 2001
From: Eduardo Broto <ebroto@tutanota.com>
Date: Fri, 15 May 2020 21:17:37 +0200
Subject: [PATCH] identity_op: allow `1 << 0`
---
clippy_lints/src/identity_op.rs | 22 ++++++++++++++++++++--
tests/ui/identity_op.rs | 5 +++++
tests/ui/identity_op.stderr | 20 +++++++++++++++++++-
3 files changed, 44 insertions(+), 3 deletions(-)
diff --git a/clippy_lints/src/identity_op.rs b/clippy_lints/src/identity_op.rs
index 088e4ab1921..78e07d25f67 100644
--- a/clippy_lints/src/identity_op.rs
+++ b/clippy_lints/src/identity_op.rs
@@ -1,4 +1,5 @@
-use rustc_hir::{BinOpKind, Expr, ExprKind};
+use if_chain::if_chain;
+use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -32,7 +33,10 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityOp {
if e.span.from_expansion() {
return;
}
- if let ExprKind::Binary(ref cmp, ref left, ref right) = e.kind {
+ if let ExprKind::Binary(cmp, ref left, ref right) = e.kind {
+ if is_allowed(cx, cmp, left, right) {
+ return;
+ }
match cmp.node {
BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
check(cx, left, 0, e.span, right.span);
@@ -54,6 +58,20 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityOp {
}
}
+fn is_allowed(cx: &LateContext<'_, '_>, cmp: BinOp, left: &Expr<'_>, right: &Expr<'_>) -> bool {
+ // `1 << 0` is a common pattern in bit manipulation code
+ if_chain! {
+ if let BinOpKind::Shl = cmp.node;
+ if let Some(Constant::Int(0)) = constant_simple(cx, cx.tables, right);
+ if let Some(Constant::Int(1)) = constant_simple(cx, cx.tables, left);
+ then {
+ return true;
+ }
+ }
+
+ false
+}
+
#[allow(clippy::cast_possible_wrap)]
fn check(cx: &LateContext<'_, '_>, e: &Expr<'_>, m: i8, span: Span, arg: Span) {
if let Some(Constant::Int(v)) = constant_simple(cx, cx.tables, e) {
diff --git a/tests/ui/identity_op.rs b/tests/ui/identity_op.rs
index ae2815d345a..ceaacaaf6bd 100644
--- a/tests/ui/identity_op.rs
+++ b/tests/ui/identity_op.rs
@@ -33,4 +33,9 @@ fn main() {
let u: u8 = 0;
u & 255;
+
+ 1 << 0; // no error, this case is allowed, see issue 3430
+ 42 << 0;
+ 1 >> 0;
+ 42 >> 0;
}
diff --git a/tests/ui/identity_op.stderr b/tests/ui/identity_op.stderr
index 4742877706a..d8d44a74f9a 100644
--- a/tests/ui/identity_op.stderr
+++ b/tests/ui/identity_op.stderr
@@ -48,5 +48,23 @@ error: the operation is ineffective. Consider reducing it to `u`
LL | u & 255;
| ^^^^^^^
-error: aborting due to 8 previous errors
+error: the operation is ineffective. Consider reducing it to `42`
+ --> $DIR/identity_op.rs:38:5
+ |
+LL | 42 << 0;
+ | ^^^^^^^
+
+error: the operation is ineffective. Consider reducing it to `1`
+ --> $DIR/identity_op.rs:39:5
+ |
+LL | 1 >> 0;
+ | ^^^^^^
+
+error: the operation is ineffective. Consider reducing it to `42`
+ --> $DIR/identity_op.rs:40:5
+ |
+LL | 42 >> 0;
+ | ^^^^^^^
+
+error: aborting due to 11 previous errors