clippy_lints/src/ptr/cmp_null.rs

use super::CMP_NULL;
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::res::{MaybeDef as _, MaybeResPath as _};
use clippy_utils::sugg::Sugg;
use clippy_utils::{is_lint_allowed, sym};
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind};
use rustc_lint::LateContext;

pub(super) fn check<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &'tcx Expr<'_>,
    op: BinOpKind,
    l: &Expr<'_>,
    r: &Expr<'_>,
) -> bool {
    let mut applicability = Applicability::MachineApplicable;
    let non_null_path_snippet = match (
        is_lint_allowed(cx, CMP_NULL, expr.hir_id),
        is_null_path(cx, l),
        is_null_path(cx, r),
    ) {
        (false, true, false) => Sugg::hir_with_context(cx, r, expr.span.ctxt(), "..", &mut applicability).maybe_paren(),
        (false, false, true) => Sugg::hir_with_context(cx, l, expr.span.ctxt(), "..", &mut applicability).maybe_paren(),
        _ => return false,
    };
    let invert = if op == BinOpKind::Eq { "" } else { "!" };

    span_lint_and_sugg(
        cx,
        CMP_NULL,
        expr.span,
        "comparing with null is better expressed by the `.is_null()` method",
        "try",
        format!("{invert}{non_null_path_snippet}.is_null()"),
        applicability,
    );
    true
}

fn is_null_path(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
    if let ExprKind::Call(pathexp, []) = expr.kind {
        matches!(
            pathexp.basic_res().opt_diag_name(cx),
            Some(sym::ptr_null | sym::ptr_null_mut)
        )
    } else {
        false
    }
}