rust-clippy/clippy_lints/src/eq_op.rs

use rustc::hir::*;
use rustc::lint::*;
use utils::{SpanlessEq, span_lint, span_lint_and_then, multispan_sugg, snippet, implements_trait};
use utils::sugg::Sugg;

/// **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_lint! {
    pub EQ_OP,
    Warn,
    "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_lint! {
    pub OP_REF,
    Warn,
    "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) {
                if SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
                    span_lint(cx,
                              EQ_OP,
                              e.span,
                              &format!("equal expressions as operands to `{}`", op.node.as_str()));
                } else {
                    let trait_id = match op.node {
                        BiAdd => cx.tcx.lang_items.add_trait(),
                        BiSub => cx.tcx.lang_items.sub_trait(),
                        BiMul => cx.tcx.lang_items.mul_trait(),
                        BiDiv => cx.tcx.lang_items.div_trait(),
                        BiRem => cx.tcx.lang_items.rem_trait(),
                        BiAnd | BiOr => None,
                        BiBitXor => cx.tcx.lang_items.bitxor_trait(),
                        BiBitAnd => cx.tcx.lang_items.bitand_trait(),
                        BiBitOr => cx.tcx.lang_items.bitor_trait(),
                        BiShl => cx.tcx.lang_items.shl_trait(),
                        BiShr => cx.tcx.lang_items.shr_trait(),
                        BiNe | BiEq => cx.tcx.lang_items.eq_trait(),
                        BiLt | BiLe | BiGe | BiGt => cx.tcx.lang_items.ord_trait(),
                    };
                    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)) => {
                                if implements_trait(cx, cx.tables.expr_ty(l), trait_id, &[cx.tables.expr_ty(r)], None) {
                                    span_lint_and_then(cx,
                                                       OP_REF,
                                                       e.span,
                                                       "taken reference of both operands, which is done automatically \
                                                        by the operator anyway",
                                                       |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)]);
                                    })
                                }
                            },
                            // &foo == bar
                            (&ExprAddrOf(_, ref l), _) => {
                                if implements_trait(cx,
                                                    cx.tables.expr_ty(l),
                                                    trait_id,
                                                    &[cx.tables.expr_ty(right)],
                                                    None) {
                                    span_lint_and_then(cx, OP_REF, e.span, "taken reference of left operand", |db| {
                                        let lsnip = snippet(cx, l.span, "...").to_string();
                                        let rsnip = Sugg::hir(cx, right, "...").deref().to_string();
                                        multispan_sugg(db,
                                                       "dereference the right operand instead".to_string(),
                                                       vec![(left.span, lsnip),
                                                            (right.span, rsnip)]);
                                    })
                                }
                            },
                            // foo == &bar
                            (_, &ExprAddrOf(_, ref r)) => {
                                if implements_trait(cx,
                                                    cx.tables.expr_ty(left),
                                                    trait_id,
                                                    &[cx.tables.expr_ty(r)],
                                                    None) {
                                    span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
                                        let lsnip = Sugg::hir(cx, left, "...").deref().to_string();
                                        let rsnip = snippet(cx, r.span, "...").to_string();
                                        multispan_sugg(db,
                                                       "dereference the left operand instead".to_string(),
                                                       vec![(left.span, lsnip),
                                                            (right.span, 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,
    }
}