clippy_lints/src/loops/for_kv_map.rs

use super::FOR_KV_MAP;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::source::snippet;
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::{pat_is_wild, sugg};
use rustc_errors::Applicability;
use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, Pat, PatKind};
use rustc_lint::LateContext;
use rustc_middle::ty;
use rustc_span::sym;

/// Checks for the `FOR_KV_MAP` lint.
pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, arg: &'tcx Expr<'_>, body: &'tcx Expr<'_>) {
    let pat_span = pat.span;

    if let PatKind::Tuple(pat, _) = pat.kind
        && pat.len() == 2
    {
        let arg_span = arg.span;
        let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
            ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
                (key, _) if pat_is_wild(cx, key, body) => (pat[1].span, "value", ty, mutbl),
                (_, value) if pat_is_wild(cx, value, body) => (pat[0].span, "key", ty, Mutability::Not),
                _ => return,
            },
            _ => return,
        };
        let mutbl = match mutbl {
            Mutability::Not => "",
            Mutability::Mut => "_mut",
        };
        let arg = match arg.kind {
            ExprKind::AddrOf(BorrowKind::Ref, _, expr) => expr,
            _ => arg,
        };

        if is_type_diagnostic_item(cx, ty, sym::HashMap) || is_type_diagnostic_item(cx, ty, sym::BTreeMap) {
            span_lint_and_then(
                cx,
                FOR_KV_MAP,
                arg_span,
                format!("you seem to want to iterate on a map's {kind}s"),
                |diag| {
                    let map = sugg::Sugg::hir(cx, arg, "map");
                    diag.multipart_suggestion(
                        "use the corresponding method",
                        vec![
                            (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
                            (arg_span, format!("{}.{kind}s{mutbl}()", map.maybe_paren())),
                        ],
                        Applicability::MachineApplicable,
                    );
                },
            );
        }
    }
}