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! {
15 /// Checks for usage of `.repeat(1)` and suggest the following method for each types.
16 /// - `.to_string()` for `str`
17 /// - `.clone()` for `String`
18 /// - `.to_vec()` for `slice`
20 /// The lint will evaluate constant expressions and values as arguments of `.repeat(..)` and emit a message if
21 /// they are equivalent to `1`. (Related discussion in [rust-clippy#7306](https://github.com/rust-lang/rust-clippy/issues/7306))
23 /// ### Why is this bad?
24 /// For example, `String.repeat(1)` is equivalent to `.clone()`. If cloning
25 /// the string is the intention behind this, `clone()` should be used.
30 /// let x = String::from("hello world").repeat(1);
36 /// let x = String::from("hello world").clone();
41 "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
44 declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
46 impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
47 fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
49 if let ExprKind::MethodCall(path, _, [receiver, count], _) = &expr.kind;
50 if path.ident.name == sym!(repeat);
51 if constant_context(cx, cx.typeck_results()).expr(count) == Some(Constant::Int(1));
52 if !in_macro(receiver.span);
54 let ty = cx.typeck_results().expr_ty(receiver).peel_refs();
60 "calling `repeat(1)` on str",
61 "consider using `.to_string()` instead",
62 format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
63 Applicability::MachineApplicable,
65 } else if ty.builtin_index().is_some() {
70 "calling `repeat(1)` on slice",
71 "consider using `.to_vec()` instead",
72 format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
73 Applicability::MachineApplicable,
75 } else if is_type_diagnostic_item(cx, ty, sym::String) {
80 "calling `repeat(1)` on a string literal",
81 "consider using `.clone()` instead",
82 format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
83 Applicability::MachineApplicable,