clippy_lints/src/methods/clear_with_drain.rs

use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::is_range_full;
use clippy_utils::ty::{is_type_diagnostic_item, is_type_lang_item};
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, LangItem, QPath};
use rustc_lint::LateContext;
use rustc_span::Span;
use rustc_span::symbol::sym;

use super::CLEAR_WITH_DRAIN;

// Add `String` here when it is added to diagnostic items
const ACCEPTABLE_TYPES_WITH_ARG: [rustc_span::Symbol; 2] = [sym::Vec, sym::VecDeque];

const ACCEPTABLE_TYPES_WITHOUT_ARG: [rustc_span::Symbol; 3] = [sym::BinaryHeap, sym::HashMap, sym::HashSet];

pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, span: Span, arg: Option<&Expr<'_>>) {
    if let Some(arg) = arg {
        if match_acceptable_type(cx, recv, &ACCEPTABLE_TYPES_WITH_ARG)
            && let ExprKind::Path(QPath::Resolved(None, container_path)) = recv.kind
            && is_range_full(cx, arg, Some(container_path))
        {
            suggest(cx, expr, recv, span);
        }
    } else if match_acceptable_type(cx, recv, &ACCEPTABLE_TYPES_WITHOUT_ARG) {
        suggest(cx, expr, recv, span);
    }
}

fn match_acceptable_type(cx: &LateContext<'_>, expr: &Expr<'_>, types: &[rustc_span::Symbol]) -> bool {
    let expr_ty = cx.typeck_results().expr_ty(expr).peel_refs();
    types.iter().any(|&ty| is_type_diagnostic_item(cx, expr_ty, ty))
    // String type is a lang item but not a diagnostic item for now so we need a separate check
        || is_type_lang_item(cx, expr_ty, LangItem::String)
}

fn suggest(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, span: Span) {
    if let Some(adt) = cx.typeck_results().expr_ty(recv).ty_adt_def()
    // Use `opt_item_name` while `String` is not a diagnostic item
        && let Some(ty_name) = cx.tcx.opt_item_name(adt.did())
    {
        span_lint_and_sugg(
            cx,
            CLEAR_WITH_DRAIN,
            span.with_hi(expr.span.hi()),
            format!("`drain` used to clear a `{ty_name}`"),
            "try",
            "clear()".to_string(),
            Applicability::MachineApplicable,
        );
    }
}