rust/clippy_lints/src/eq_op.rs
2018-03-28 15:24:26 +02:00

163 lines
7.4 KiB
Rust

use rustc::hir::*;
use rustc::lint::*;
use utils::{in_macro, implements_trait, is_copy, multispan_sugg, snippet, span_lint, span_lint_and_then, SpanlessEq};
/// **What it does:** Checks for equal operands to comparison, logical and
/// bitwise, difference and division binary operators (`==`, `>`, etc., `&&`,
/// `||`, `&`, `|`, `^`, `-` and `/`).
///
/// **Why is this bad?** This is usually just a typo or a copy and paste error.
///
/// **Known problems:** False negatives: We had some false positives regarding
/// calls (notably [racer](https://github.com/phildawes/racer) had one instance
/// of `x.pop() && x.pop()`), so we removed matching any function or method
/// calls. We may introduce a whitelist of known pure functions in the future.
///
/// **Example:**
/// ```rust
/// x + 1 == x + 1
/// ```
declare_clippy_lint! {
pub EQ_OP,
correctness,
"equal operands on both sides of a comparison or bitwise combination (e.g. `x == x`)"
}
/// **What it does:** Checks for arguments to `==` which have their address
/// taken to satisfy a bound
/// and suggests to dereference the other argument instead
///
/// **Why is this bad?** It is more idiomatic to dereference the other argument.
///
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// &x == y
/// ```
declare_clippy_lint! {
pub OP_REF,
style,
"taking a reference to satisfy the type constraints on `==`"
}
#[derive(Copy, Clone)]
pub struct EqOp;
impl LintPass for EqOp {
fn get_lints(&self) -> LintArray {
lint_array!(EQ_OP, OP_REF)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EqOp {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
if let ExprBinary(ref op, ref left, ref right) = e.node {
if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) && !in_macro(e.span) {
span_lint(
cx,
EQ_OP,
e.span,
&format!("equal expressions as operands to `{}`", op.node.as_str()),
);
return;
}
let (trait_id, requires_ref) = match op.node {
BiAdd => (cx.tcx.lang_items().add_trait(), false),
BiSub => (cx.tcx.lang_items().sub_trait(), false),
BiMul => (cx.tcx.lang_items().mul_trait(), false),
BiDiv => (cx.tcx.lang_items().div_trait(), false),
BiRem => (cx.tcx.lang_items().rem_trait(), false),
// don't lint short circuiting ops
BiAnd | BiOr => return,
BiBitXor => (cx.tcx.lang_items().bitxor_trait(), false),
BiBitAnd => (cx.tcx.lang_items().bitand_trait(), false),
BiBitOr => (cx.tcx.lang_items().bitor_trait(), false),
BiShl => (cx.tcx.lang_items().shl_trait(), false),
BiShr => (cx.tcx.lang_items().shr_trait(), false),
BiNe | BiEq => (cx.tcx.lang_items().eq_trait(), true),
BiLt | BiLe | BiGe | BiGt => (cx.tcx.lang_items().ord_trait(), true),
};
if let Some(trait_id) = trait_id {
#[allow(match_same_arms)]
match (&left.node, &right.node) {
// do not suggest to dereference literals
(&ExprLit(..), _) | (_, &ExprLit(..)) => {},
// &foo == &bar
(&ExprAddrOf(_, ref l), &ExprAddrOf(_, ref r)) => {
let lty = cx.tables.expr_ty(l);
let rty = cx.tables.expr_ty(r);
let lcpy = is_copy(cx, lty);
let rcpy = is_copy(cx, rty);
// either operator autorefs or both args are copyable
if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty]) {
span_lint_and_then(
cx,
OP_REF,
e.span,
"needlessly taken reference of both operands",
|db| {
let lsnip = snippet(cx, l.span, "...").to_string();
let rsnip = snippet(cx, r.span, "...").to_string();
multispan_sugg(
db,
"use the values directly".to_string(),
vec![(left.span, lsnip), (right.span, rsnip)],
);
},
)
} else if lcpy && !rcpy && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right)]) {
span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
let lsnip = snippet(cx, l.span, "...").to_string();
db.span_suggestion(left.span, "use the left value directly", lsnip);
})
} else if !lcpy && rcpy && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty]) {
span_lint_and_then(
cx,
OP_REF,
e.span,
"needlessly taken reference of right operand",
|db| {
let rsnip = snippet(cx, r.span, "...").to_string();
db.span_suggestion(right.span, "use the right value directly", rsnip);
},
)
}
},
// &foo == bar
(&ExprAddrOf(_, ref l), _) => {
let lty = cx.tables.expr_ty(l);
let lcpy = is_copy(cx, lty);
if (requires_ref || lcpy) && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right)]) {
span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
let lsnip = snippet(cx, l.span, "...").to_string();
db.span_suggestion(left.span, "use the left value directly", lsnip);
})
}
},
// foo == &bar
(_, &ExprAddrOf(_, ref r)) => {
let rty = cx.tables.expr_ty(r);
let rcpy = is_copy(cx, rty);
if (requires_ref || rcpy) && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty]) {
span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
let rsnip = snippet(cx, r.span, "...").to_string();
db.span_suggestion(right.span, "use the right value directly", rsnip);
})
}
},
_ => {},
}
}
}
}
}
fn is_valid_operator(op: &BinOp) -> bool {
match op.node {
BiSub | BiDiv | BiEq | BiLt | BiLe | BiGt | BiGe | BiNe | BiAnd | BiOr | BiBitXor | BiBitAnd | BiBitOr => true,
_ => false,
}
}