1 use clippy_utils::consts::{constant_context, Constant};
2 use clippy_utils::diagnostics::span_lint_and_sugg;
3 use clippy_utils::in_macro;
4 use clippy_utils::source::snippet;
5 use clippy_utils::ty::is_type_diagnostic_item;
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::{Expr, ExprKind};
9 use rustc_lint::{LateContext, LateLintPass};
10 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 declare_clippy_lint! {
14 /// **What it does:** Checks for usage of `.repeat(1)` and suggest the following method for each types.
15 /// - `.to_string()` for `str`
16 /// - `.clone()` for `String`
17 /// - `.to_vec()` for `slice`
19 /// The lint will evaluate constant expressions and values as arguments of `.repeat(..)` and emit a message if
20 /// they are equivalent to `1`. (Related discussion in [rust-clippy#7306](https://github.com/rust-lang/rust-clippy/issues/7306))
22 /// **Why is this bad?** For example, `String.repeat(1)` is equivalent to `.clone()`. If cloning
23 /// the string is the intention behind this, `clone()` should be used.
25 /// **Known problems:** None.
31 /// let x = String::from("hello world").repeat(1);
37 /// let x = String::from("hello world").clone();
42 "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
45 declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
47 impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
48 fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
50 if let ExprKind::MethodCall(path, _, [receiver, count], _) = &expr.kind;
51 if path.ident.name == sym!(repeat);
52 if let Some(Constant::Int(1)) = constant_context(cx, cx.typeck_results()).expr(count);
53 if !in_macro(receiver.span);
55 let ty = cx.typeck_results().expr_ty(receiver).peel_refs();
61 "calling `repeat(1)` on str",
62 "consider using `.to_string()` instead",
63 format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
64 Applicability::MachineApplicable,
66 } else if ty.builtin_index().is_some() {
71 "calling `repeat(1)` on slice",
72 "consider using `.to_vec()` instead",
73 format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
74 Applicability::MachineApplicable,
76 } else if is_type_diagnostic_item(cx, ty, sym::string_type) {
81 "calling `repeat(1)` on a string literal",
82 "consider using `.clone()` instead",
83 format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
84 Applicability::MachineApplicable,