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use rustc::hir::*;
use rustc::lint::*;
use utils::{SpanlessEq, span_lint};

/// **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`)"
}

#[derive(Copy,Clone)]
pub struct EqOp;

impl LintPass for EqOp {
    fn get_lints(&self) -> LintArray {
        lint_array!(EQ_OP)
    }
}

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) {
                span_lint(cx,
                          EQ_OP,
                          e.span,
                          &format!("equal expressions as operands to `{}`", op.node.as_str()));
            }
        }
    }
}


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,
    }
}