arity 0.5.0

An LSP, formatter, and linter for R
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//! `equals-na`: `x == NA` is always `NA`, never `TRUE`/`FALSE` — almost always
//! a mistake for `is.na(x)`. Only the `==` form is rewritten; `!=` is left for a
//! separate rule.

use crate::linter::diagnostic::{Diagnostic, Fix, Severity, ViolationData};
use crate::linter::rules::matchers;
use crate::linter::rules::{Rule, RuleContext};
use crate::syntax::{SyntaxElement, SyntaxKind};

pub struct EqualsNa;

impl Rule for EqualsNa {
    fn id(&self) -> &'static str {
        "equals-na"
    }

    fn interests(&self) -> &'static [SyntaxKind] {
        &[SyntaxKind::BINARY_EXPR]
    }

    fn check(&self, el: &SyntaxElement, _ctx: &RuleContext<'_>, sink: &mut Vec<Diagnostic>) {
        let Some(node) = el.as_node() else {
            return;
        };
        let Some((lhs, op, rhs)) = matchers::binary_parts(node) else {
            return;
        };
        if op.kind() != SyntaxKind::EQUAL2 {
            return;
        }
        // The non-`NA` operand; bail unless exactly one side is `NA`.
        let other = match (matchers::is_na(&lhs), matchers::is_na(&rhs)) {
            (true, false) => &rhs,
            (false, true) => &lhs,
            _ => return,
        };
        let r = node.text_range();
        // `is.na(<other>)` parenthesizes the operand, so no precedence guard.
        let fix = Fix::safe(
            usize::from(r.start()),
            usize::from(r.end()),
            format!("is.na({})", matchers::element_text(other)),
            "Replace `== NA` with `is.na()`",
        );
        sink.push(Diagnostic {
            rule: "equals-na",
            severity: Severity::Warning,
            path: Default::default(),
            range: r,
            message: ViolationData::new(
                "equals-na",
                "comparison with `NA` is always `NA`; use `is.na()`",
            )
            .with_suggestion("Use `is.na(x)`."),
            fix: Some(fix),
        });
    }
}