clippy_lints/src/methods/manual_str_repeat.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::is_path_diagnostic_item;
   3 use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
   4 use clippy_utils::sugg::Sugg;
   5 use clippy_utils::ty::{is_type_diagnostic_item, is_type_lang_item};
   6 use if_chain::if_chain;
   7 use rustc_ast::LitKind;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::{Expr, ExprKind, LangItem};
  10 use rustc_lint::LateContext;
  11 use rustc_middle::ty::{self, Ty};
  12 use rustc_span::symbol::sym;
  13 use std::borrow::Cow;
  14
  15 use super::MANUAL_STR_REPEAT;
  16
  17 enum RepeatKind {
  18     String,
  19     Char(char),
  20 }
  21
  22 fn get_ty_param(ty: Ty<'_>) -> Option<Ty<'_>> {
  23     if let ty::Adt(_, subs) = ty.kind() {
  24         subs.types().next()
  25     } else {
  26         None
  27     }
  28 }
  29
  30 fn parse_repeat_arg(cx: &LateContext<'_>, e: &Expr<'_>) -> Option<RepeatKind> {
  31     if let ExprKind::Lit(lit) = &e.kind {
  32         match lit.node {
  33             LitKind::Str(..) => Some(RepeatKind::String),
  34             LitKind::Char(c) => Some(RepeatKind::Char(c)),
  35             _ => None,
  36         }
  37     } else {
  38         let ty = cx.typeck_results().expr_ty(e);
  39         if is_type_lang_item(cx, ty, LangItem::String)
  40             || (is_type_lang_item(cx, ty, LangItem::OwnedBox) && get_ty_param(ty).map_or(false, Ty::is_str))
  41             || (is_type_diagnostic_item(cx, ty, sym::Cow) && get_ty_param(ty).map_or(false, Ty::is_str))
  42         {
  43             Some(RepeatKind::String)
  44         } else {
  45             let ty = ty.peel_refs();
  46             (ty.is_str() || is_type_lang_item(cx, ty, LangItem::String)).then_some(RepeatKind::String)
  47         }
  48     }
  49 }
  50
  51 pub(super) fn check(
  52     cx: &LateContext<'_>,
  53     collect_expr: &Expr<'_>,
  54     take_expr: &Expr<'_>,
  55     take_self_arg: &Expr<'_>,
  56     take_arg: &Expr<'_>,
  57 ) {
  58     if_chain! {
  59         if let ExprKind::Call(repeat_fn, [repeat_arg]) = take_self_arg.kind;
  60         if is_path_diagnostic_item(cx, repeat_fn, sym::iter_repeat);
  61         if is_type_lang_item(cx, cx.typeck_results().expr_ty(collect_expr), LangItem::String);
  62         if let Some(take_id) = cx.typeck_results().type_dependent_def_id(take_expr.hir_id);
  63         if let Some(iter_trait_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
  64         if cx.tcx.trait_of_item(take_id) == Some(iter_trait_id);
  65         if let Some(repeat_kind) = parse_repeat_arg(cx, repeat_arg);
  66         let ctxt = collect_expr.span.ctxt();
  67         if ctxt == take_expr.span.ctxt();
  68         if ctxt == take_self_arg.span.ctxt();
  69         then {
  70             let mut app = Applicability::MachineApplicable;
  71             let count_snip = snippet_with_context(cx, take_arg.span, ctxt, "..", &mut app).0;
  72
  73             let val_str = match repeat_kind {
  74                 RepeatKind::Char(_) if repeat_arg.span.ctxt() != ctxt => return,
  75                 RepeatKind::Char('\'') => r#""'""#.into(),
  76                 RepeatKind::Char('"') => r#""\"""#.into(),
  77                 RepeatKind::Char(_) =>
  78                     match snippet_with_applicability(cx, repeat_arg.span, "..", &mut app) {
  79                         Cow::Owned(s) => Cow::Owned(format!("\"{}\"", &s[1..s.len() - 1])),
  80                         s @ Cow::Borrowed(_) => s,
  81                     },
  82                 RepeatKind::String =>
  83                     Sugg::hir_with_context(cx, repeat_arg, ctxt, "..", &mut app).maybe_par().to_string().into(),
  84             };
  85
  86             span_lint_and_sugg(
  87                 cx,
  88                 MANUAL_STR_REPEAT,
  89                 collect_expr.span,
  90                 "manual implementation of `str::repeat` using iterators",
  91                 "try this",
  92                 format!("{val_str}.repeat({count_snip})"),
  93                 app
  94             )
  95         }
  96     }
  97 }