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::source::snippet;
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use if_chain::if_chain;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{Expr, ExprKind};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::sym;
  11
  12 declare_clippy_lint! {
  13     /// ### What it does
  14     /// 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`
  18     ///
  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))
  21     ///
  22     /// ### Why is this bad?
  23     /// For example, `String.repeat(1)` is equivalent to `.clone()`. If cloning
  24     /// the string is the intention behind this, `clone()` should be used.
  25     ///
  26     /// ### Example
  27     /// ```rust
  28     /// fn main() {
  29     ///     let x = String::from("hello world").repeat(1);
  30     /// }
  31     /// ```
  32     /// Use instead:
  33     /// ```rust
  34     /// fn main() {
  35     ///     let x = String::from("hello world").clone();
  36     /// }
  37     /// ```
  38     pub REPEAT_ONCE,
  39     complexity,
  40     "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
  41 }
  42
  43 declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
  44
  45 impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
  46     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
  47         if_chain! {
  48             if let ExprKind::MethodCall(path, _, [receiver, count], _) = &expr.kind;
  49             if path.ident.name == sym!(repeat);
  50             if constant_context(cx, cx.typeck_results()).expr(count) == Some(Constant::Int(1));
  51             if !receiver.span.from_expansion();
  52             then {
  53                 let ty = cx.typeck_results().expr_ty(receiver).peel_refs();
  54                 if ty.is_str() {
  55                     span_lint_and_sugg(
  56                         cx,
  57                         REPEAT_ONCE,
  58                         expr.span,
  59                         "calling `repeat(1)` on str",
  60                         "consider using `.to_string()` instead",
  61                         format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
  62                         Applicability::MachineApplicable,
  63                     );
  64                 } else if ty.builtin_index().is_some() {
  65                     span_lint_and_sugg(
  66                         cx,
  67                         REPEAT_ONCE,
  68                         expr.span,
  69                         "calling `repeat(1)` on slice",
  70                         "consider using `.to_vec()` instead",
  71                         format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
  72                         Applicability::MachineApplicable,
  73                     );
  74                 } else if is_type_diagnostic_item(cx, ty, sym::String) {
  75                     span_lint_and_sugg(
  76                         cx,
  77                         REPEAT_ONCE,
  78                         expr.span,
  79                         "calling `repeat(1)` on a string literal",
  80                         "consider using `.clone()` instead",
  81                         format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
  82                         Applicability::MachineApplicable,
  83                     );
  84                 }
  85             }
  86         }
  87     }
  88 }