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:** 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?** For example, `String.repeat(1)` is equivalent to `.clone()`. If cloning
  23     /// the string is the intention behind this, `clone()` should be used.
  24     ///
  25     /// **Known problems:** None.
  26     ///
  27     /// **Example:**
  28     ///
  29     /// ```rust
  30     /// fn main() {
  31     ///     let x = String::from("hello world").repeat(1);
  32     /// }
  33     /// ```
  34     /// Use instead:
  35     /// ```rust
  36     /// fn main() {
  37     ///     let x = String::from("hello world").clone();
  38     /// }
  39     /// ```
  40     pub REPEAT_ONCE,
  41     complexity,
  42     "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
  43 }
  44
  45 declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
  46
  47 impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
  48     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
  49         if_chain! {
  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);
  54             then {
  55                 let ty = cx.typeck_results().expr_ty(receiver).peel_refs();
  56                 if ty.is_str() {
  57                     span_lint_and_sugg(
  58                         cx,
  59                         REPEAT_ONCE,
  60                         expr.span,
  61                         "calling `repeat(1)` on str",
  62                         "consider using `.to_string()` instead",
  63                         format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
  64                         Applicability::MachineApplicable,
  65                     );
  66                 } else if ty.builtin_index().is_some() {
  67                     span_lint_and_sugg(
  68                         cx,
  69                         REPEAT_ONCE,
  70                         expr.span,
  71                         "calling `repeat(1)` on slice",
  72                         "consider using `.to_vec()` instead",
  73                         format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
  74                         Applicability::MachineApplicable,
  75                     );
  76                 } else if is_type_diagnostic_item(cx, ty, sym::string_type) {
  77                     span_lint_and_sugg(
  78                         cx,
  79                         REPEAT_ONCE,
  80                         expr.span,
  81                         "calling `repeat(1)` on a string literal",
  82                         "consider using `.clone()` instead",
  83                         format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
  84                         Applicability::MachineApplicable,
  85                     );
  86                 }
  87             }
  88         }
  89     }
  90 }