clippy_lints/src/repeat_once.rs

   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};
  11 use rustc_span::sym;
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  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`
  19     ///
  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))
  22     ///
  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.
  26     ///
  27     /// ### Example
  28     /// ```rust
  29     /// fn main() {
  30     ///     let x = String::from("hello world").repeat(1);
  31     /// }
  32     /// ```
  33     /// Use instead:
  34     /// ```rust
  35     /// fn main() {
  36     ///     let x = String::from("hello world").clone();
  37     /// }
  38     /// ```
  39     pub REPEAT_ONCE,
  40     complexity,
  41     "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
  42 }
  43
  44 declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
  45
  46 impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
  47     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
  48         if_chain! {
  49             if let ExprKind::MethodCall(path, _, [receiver, count], _) = &expr.kind;
  50             if path.ident.name == sym!(repeat);
  51             if let Some(Constant::Int(1)) = constant_context(cx, cx.typeck_results()).expr(count);
  52             if !in_macro(receiver.span);
  53             then {
  54                 let ty = cx.typeck_results().expr_ty(receiver).peel_refs();
  55                 if ty.is_str() {
  56                     span_lint_and_sugg(
  57                         cx,
  58                         REPEAT_ONCE,
  59                         expr.span,
  60                         "calling `repeat(1)` on str",
  61                         "consider using `.to_string()` instead",
  62                         format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
  63                         Applicability::MachineApplicable,
  64                     );
  65                 } else if ty.builtin_index().is_some() {
  66                     span_lint_and_sugg(
  67                         cx,
  68                         REPEAT_ONCE,
  69                         expr.span,
  70                         "calling `repeat(1)` on slice",
  71                         "consider using `.to_vec()` instead",
  72                         format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
  73                         Applicability::MachineApplicable,
  74                     );
  75                 } else if is_type_diagnostic_item(cx, ty, sym::string_type) {
  76                     span_lint_and_sugg(
  77                         cx,
  78                         REPEAT_ONCE,
  79                         expr.span,
  80                         "calling `repeat(1)` on a string literal",
  81                         "consider using `.clone()` instead",
  82                         format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
  83                         Applicability::MachineApplicable,
  84                     );
  85                 }
  86             }
  87         }
  88     }
  89 }