clippy_lints/src/methods/map_collect_result_unit.rs

use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::res::MaybeDef;
use clippy_utils::source::snippet;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_lint::LateContext;
use rustc_middle::ty;
use rustc_span::symbol::sym;

use super::MAP_COLLECT_RESULT_UNIT;

pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, iter: &hir::Expr<'_>, map_fn: &hir::Expr<'_>) {
    // return of collect `Result<(),_>`
    let collect_ret_ty = cx.typeck_results().expr_ty(expr);
    if collect_ret_ty.is_diag_item(cx, sym::Result)
        && let ty::Adt(_, args) = collect_ret_ty.kind()
        && let Some(result_t) = args.types().next()
        && result_t.is_unit()
    // get parts for snippet
    {
        span_lint_and_sugg(
            cx,
            MAP_COLLECT_RESULT_UNIT,
            expr.span,
            "`.map().collect()` can be replaced with `.try_for_each()`",
            "try",
            format!(
                "{}.try_for_each({})",
                snippet(cx, iter.span, ".."),
                snippet(cx, map_fn.span, "..")
            ),
            Applicability::MachineApplicable,
        );
    }
}