Move ErasingOp into Operators lint pass

Author: Jarcho

clippy_lints/src/erasing_op.rs

@@ -60,7 +60,6 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(enum_clike::ENUM_CLIKE_UNPORTABLE_VARIANT),
     LintId::of(enum_variants::ENUM_VARIANT_NAMES),
     LintId::of(enum_variants::MODULE_INCEPTION),
-    LintId::of(erasing_op::ERASING_OP),
     LintId::of(escape::BOXED_LOCAL),
     LintId::of(eta_reduction::REDUNDANT_CLOSURE),
     LintId::of(explicit_write::EXPLICIT_WRITE),
@@ -250,6 +249,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(operators::DOUBLE_COMPARISONS),
     LintId::of(operators::DURATION_SUBSEC),
     LintId::of(operators::EQ_OP),
+    LintId::of(operators::ERASING_OP),
     LintId::of(operators::INEFFECTIVE_BIT_MASK),
     LintId::of(operators::MISREFACTORED_ASSIGN_OP),
     LintId::of(operators::OP_REF),

clippy_lints/src/lib.register_all.rs

@@ -21,7 +21,6 @@ store.register_group(true, "clippy::correctness", Some("clippy_correctness"), ve
     LintId::of(drop_forget_ref::FORGET_REF),
     LintId::of(drop_forget_ref::UNDROPPED_MANUALLY_DROPS),
     LintId::of(enum_clike::ENUM_CLIKE_UNPORTABLE_VARIANT),
-    LintId::of(erasing_op::ERASING_OP),
     LintId::of(format_impl::RECURSIVE_FORMAT_IMPL),
     LintId::of(formatting::POSSIBLE_MISSING_COMMA),
     LintId::of(functions::NOT_UNSAFE_PTR_ARG_DEREF),
@@ -50,6 +49,7 @@ store.register_group(true, "clippy::correctness", Some("clippy_correctness"), ve
     LintId::of(operators::ABSURD_EXTREME_COMPARISONS),
     LintId::of(operators::BAD_BIT_MASK),
     LintId::of(operators::EQ_OP),
+    LintId::of(operators::ERASING_OP),
     LintId::of(operators::INEFFECTIVE_BIT_MASK),
     LintId::of(option_env_unwrap::OPTION_ENV_UNWRAP),
     LintId::of(ptr::INVALID_NULL_PTR_USAGE),

clippy_lints/src/lib.register_correctness.rs

@@ -137,7 +137,6 @@ store.register_lints(&[
     enum_variants::MODULE_INCEPTION,
     enum_variants::MODULE_NAME_REPETITIONS,
     equatable_if_let::EQUATABLE_IF_LET,
-    erasing_op::ERASING_OP,
     escape::BOXED_LOCAL,
     eta_reduction::REDUNDANT_CLOSURE,
     eta_reduction::REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
@@ -419,6 +418,7 @@ store.register_lints(&[
     operators::DOUBLE_COMPARISONS,
     operators::DURATION_SUBSEC,
     operators::EQ_OP,
+    operators::ERASING_OP,
     operators::FLOAT_ARITHMETIC,
     operators::INEFFECTIVE_BIT_MASK,
     operators::INTEGER_ARITHMETIC,

clippy_lints/src/lib.register_lints.rs

@@ -217,7 +217,6 @@ mod entry;
 mod enum_clike;
 mod enum_variants;
 mod equatable_if_let;
-mod erasing_op;
 mod escape;
 mod eta_reduction;
 mod excessive_bools;
@@ -550,7 +549,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| Box::new(misc::MiscLints));
     store.register_late_pass(|| Box::new(eta_reduction::EtaReduction));
     store.register_late_pass(|| Box::new(identity_op::IdentityOp));
-    store.register_late_pass(|| Box::new(erasing_op::ErasingOp));
     store.register_late_pass(|| Box::new(mut_mut::MutMut));
     store.register_late_pass(|| Box::new(mut_reference::UnnecessaryMutPassed));
     store.register_late_pass(|| Box::new(len_zero::LenZero));

clippy_lints/src/lib.rs

@@ -0,0 +1,53 @@
+use clippy_utils::consts::{constant_simple, Constant};
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::ty::same_type_and_consts;
+
+use rustc_hir::{BinOpKind, Expr};
+use rustc_lint::LateContext;
+use rustc_middle::ty::TypeckResults;
+
+use super::ERASING_OP;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    e: &'tcx Expr<'_>,
+    op: BinOpKind,
+    left: &'tcx Expr<'_>,
+    right: &'tcx Expr<'_>,
+) {
+    let tck = cx.typeck_results();
+    match op {
+        BinOpKind::Mul | BinOpKind::BitAnd => {
+            check_op(cx, tck, left, right, e);
+            check_op(cx, tck, right, left, e);
+        },
+        BinOpKind::Div => check_op(cx, tck, left, right, e),
+        _ => (),
+    }
+}
+
+fn different_types(tck: &TypeckResults<'_>, input: &Expr<'_>, output: &Expr<'_>) -> bool {
+    let input_ty = tck.expr_ty(input).peel_refs();
+    let output_ty = tck.expr_ty(output).peel_refs();
+    !same_type_and_consts(input_ty, output_ty)
+}
+
+fn check_op<'tcx>(
+    cx: &LateContext<'tcx>,
+    tck: &TypeckResults<'tcx>,
+    op: &Expr<'tcx>,
+    other: &Expr<'tcx>,
+    parent: &Expr<'tcx>,
+) {
+    if constant_simple(cx, tck, op) == Some(Constant::Int(0)) {
+        if different_types(tck, other, parent) {
+            return;
+        }
+        span_lint(
+            cx,
+            ERASING_OP,
+            parent.span,
+            "this operation will always return zero. This is likely not the intended outcome",
+        );
+    }
+}

clippy_lints/src/operators/erasing_op.rs

@@ -9,6 +9,7 @@ mod bit_mask;
 mod double_comparison;
 mod duration_subsec;
 mod eq_op;
+mod erasing_op;
 mod misrefactored_assign_op;
 mod op_ref;
 mod verbose_bit_mask;
@@ -354,6 +355,28 @@ declare_clippy_lint! {
     "taking a reference to satisfy the type constraints on `==`"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for erasing operations, e.g., `x * 0`.
+    ///
+    /// ### Why is this bad?
+    /// The whole expression can be replaced by zero.
+    /// This is most likely not the intended outcome and should probably be
+    /// corrected
+    ///
+    /// ### Example
+    /// ```rust
+    /// let x = 1;
+    /// 0 / x;
+    /// 0 * x;
+    /// x & 0;
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
+    pub ERASING_OP,
+    correctness,
+    "using erasing operations, e.g., `x * 0` or `y & 0`"
+}
+
 pub struct Operators {
     arithmetic_context: arithmetic::Context,
     verbose_bit_mask_threshold: u64,
@@ -371,6 +394,7 @@ impl_lint_pass!(Operators => [
     DURATION_SUBSEC,
     EQ_OP,
     OP_REF,
+    ERASING_OP,
 ]);
 impl Operators {
     pub fn new(verbose_bit_mask_threshold: u64) -> Self {
@@ -391,6 +415,7 @@ impl<'tcx> LateLintPass<'tcx> for Operators {
                         eq_op::check(cx, e, op.node, lhs, rhs);
                         op_ref::check(cx, e, op.node, lhs, rhs);
                     }
+                    erasing_op::check(cx, e, op.node, lhs, rhs);
                 }
                 self.arithmetic_context.check_binary(cx, e, op.node, lhs, rhs);
                 bit_mask::check(cx, e, op.node, lhs, rhs);