rust/clippy_lints/src/methods/manual_str_repeat.rs

use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
use clippy_utils::sugg::Sugg;
use clippy_utils::ty::{is_type_diagnostic_item, is_type_lang_item, match_type};
use clippy_utils::{is_expr_path_def_path, paths};
use if_chain::if_chain;
use rustc_ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, LangItem};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, Ty};
use rustc_span::symbol::sym;
use std::borrow::Cow;

use super::MANUAL_STR_REPEAT;

enum RepeatKind {
    String,
    Char(char),
}

fn get_ty_param(ty: Ty<'_>) -> Option<Ty<'_>> {
    if let ty::Adt(_, subs) = ty.kind() {
        subs.types().next()
    } else {
        None
    }
}

fn parse_repeat_arg(cx: &LateContext<'_>, e: &Expr<'_>) -> Option<RepeatKind> {
    if let ExprKind::Lit(lit) = &e.kind {
        match lit.node {
            LitKind::Str(..) => Some(RepeatKind::String),
            LitKind::Char(c) => Some(RepeatKind::Char(c)),
            _ => None,
        }
    } else {
        let ty = cx.typeck_results().expr_ty(e);
        if is_type_diagnostic_item(cx, ty, sym::String)
            || (is_type_lang_item(cx, ty, LangItem::OwnedBox) && get_ty_param(ty).map_or(false, Ty::is_str))
            || (match_type(cx, ty, &paths::COW) && get_ty_param(ty).map_or(false, Ty::is_str))
        {
            Some(RepeatKind::String)
        } else {
            let ty = ty.peel_refs();
            (ty.is_str() || is_type_diagnostic_item(cx, ty, sym::String)).then(|| RepeatKind::String)
        }
    }
}

pub(super) fn check(
    cx: &LateContext<'_>,
    collect_expr: &Expr<'_>,
    take_expr: &Expr<'_>,
    take_self_arg: &Expr<'_>,
    take_arg: &Expr<'_>,
) {
    if_chain! {
        if let ExprKind::Call(repeat_fn, [repeat_arg]) = take_self_arg.kind;
        if is_expr_path_def_path(cx, repeat_fn, &paths::ITER_REPEAT);
        if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(collect_expr), sym::String);
        if let Some(collect_id) = cx.typeck_results().type_dependent_def_id(collect_expr.hir_id);
        if let Some(take_id) = cx.typeck_results().type_dependent_def_id(take_expr.hir_id);
        if let Some(iter_trait_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
        if cx.tcx.trait_of_item(collect_id) == Some(iter_trait_id);
        if cx.tcx.trait_of_item(take_id) == Some(iter_trait_id);
        if let Some(repeat_kind) = parse_repeat_arg(cx, repeat_arg);
        let ctxt = collect_expr.span.ctxt();
        if ctxt == take_expr.span.ctxt();
        if ctxt == take_self_arg.span.ctxt();
        then {
            let mut app = Applicability::MachineApplicable;
            let count_snip = snippet_with_context(cx, take_arg.span, ctxt, "..", &mut app).0;

            let val_str = match repeat_kind {
                RepeatKind::Char(_) if repeat_arg.span.ctxt() != ctxt => return,
                RepeatKind::Char('\'') => r#""'""#.into(),
                RepeatKind::Char('"') => r#""\"""#.into(),
                RepeatKind::Char(_) =>
                    match snippet_with_applicability(cx, repeat_arg.span, "..", &mut app) {
                        Cow::Owned(s) => Cow::Owned(format!("\"{}\"", &s[1..s.len() - 1])),
                        s @ Cow::Borrowed(_) => s,
                    },
                RepeatKind::String =>
                    Sugg::hir_with_context(cx, repeat_arg, ctxt, "..", &mut app).maybe_par().to_string().into(),
            };

            span_lint_and_sugg(
                cx,
                MANUAL_STR_REPEAT,
                collect_expr.span,
                "manual implementation of `str::repeat` using iterators",
                "try this",
                format!("{}.repeat({})", val_str, count_snip),
                app
            )
        }
    }
}