clippy_lints/src/repeat_once.rs

   1 use crate::consts::{constant_context, Constant};
   2 use crate::utils::{in_macro, 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:** Checks for usage of `.repeat(1)` and suggest the following method for each types.
  14     /// - `.to_string()` for `str`
  15     /// - `.clone()` for `String`
  16     /// - `.to_vec()` for `slice`
  17     ///
  18     /// **Why is this bad?** For example, `String.repeat(1)` is equivalent to `.clone()`. If cloning the string is the intention behind this, `clone()` should be used.
  19     ///
  20     /// **Known problems:** None.
  21     ///
  22     /// **Example:**
  23     ///
  24     /// ```rust
  25     /// fn main() {
  26     ///     let x = String::from("hello world").repeat(1);
  27     /// }
  28     /// ```
  29     /// Use instead:
  30     /// ```rust
  31     /// fn main() {
  32     ///     let x = String::from("hello world").clone();
  33     /// }
  34     /// ```
  35     pub REPEAT_ONCE,
  36     complexity,
  37     "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
  38 }
  39
  40 declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
  41
  42 impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
  43     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
  44         if_chain! {
  45             if let ExprKind::MethodCall(path, _, [receiver, count], _) = &expr.kind;
  46             if path.ident.name == sym!(repeat);
  47             if let Some(Constant::Int(1)) = constant_context(cx, cx.typeck_results()).expr(&count);
  48             if !in_macro(receiver.span);
  49             then {
  50                 let ty = cx.typeck_results().expr_ty(&receiver).peel_refs();
  51                 if ty.is_str() {
  52                     span_lint_and_sugg(
  53                         cx,
  54                         REPEAT_ONCE,
  55                         expr.span,
  56                         "calling `repeat(1)` on str",
  57                         "consider using `.to_string()` instead",
  58                         format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
  59                         Applicability::MachineApplicable,
  60                     );
  61                 } else if ty.builtin_index().is_some() {
  62                     span_lint_and_sugg(
  63                         cx,
  64                         REPEAT_ONCE,
  65                         expr.span,
  66                         "calling `repeat(1)` on slice",
  67                         "consider using `.to_vec()` instead",
  68                         format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
  69                         Applicability::MachineApplicable,
  70                     );
  71                 } else if is_type_diagnostic_item(cx, ty, sym::string_type) {
  72                     span_lint_and_sugg(
  73                         cx,
  74                         REPEAT_ONCE,
  75                         expr.span,
  76                         "calling `repeat(1)` on a string literal",
  77                         "consider using `.clone()` instead",
  78                         format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
  79                         Applicability::MachineApplicable,
  80                     );
  81                 }
  82             }
  83         }
  84     }
  85 }