clippy_lints/src/repeat_once.rs

   1 use crate::consts::{constant_context, Constant};
   2 use crate::utils::{in_macro, snippet, span_lint_and_sugg};
   3 use clippy_utils::ty::is_type_diagnostic_item;
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{Expr, ExprKind};
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_session::{declare_lint_pass, declare_tool_lint};
   9 use rustc_span::sym;
  10
  11 declare_clippy_lint! {
  12     /// **What it does:** Checks for usage of `.repeat(1)` and suggest the following method for each types.
  13     /// - `.to_string()` for `str`
  14     /// - `.clone()` for `String`
  15     /// - `.to_vec()` for `slice`
  16     ///
  17     /// **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.
  18     ///
  19     /// **Known problems:** None.
  20     ///
  21     /// **Example:**
  22     ///
  23     /// ```rust
  24     /// fn main() {
  25     ///     let x = String::from("hello world").repeat(1);
  26     /// }
  27     /// ```
  28     /// Use instead:
  29     /// ```rust
  30     /// fn main() {
  31     ///     let x = String::from("hello world").clone();
  32     /// }
  33     /// ```
  34     pub REPEAT_ONCE,
  35     complexity,
  36     "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
  37 }
  38
  39 declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
  40
  41 impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
  42     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
  43         if_chain! {
  44             if let ExprKind::MethodCall(path, _, [receiver, count], _) = &expr.kind;
  45             if path.ident.name == sym!(repeat);
  46             if let Some(Constant::Int(1)) = constant_context(cx, cx.typeck_results()).expr(&count);
  47             if !in_macro(receiver.span);
  48             then {
  49                 let ty = cx.typeck_results().expr_ty(&receiver).peel_refs();
  50                 if ty.is_str() {
  51                     span_lint_and_sugg(
  52                         cx,
  53                         REPEAT_ONCE,
  54                         expr.span,
  55                         "calling `repeat(1)` on str",
  56                         "consider using `.to_string()` instead",
  57                         format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
  58                         Applicability::MachineApplicable,
  59                     );
  60                 } else if ty.builtin_index().is_some() {
  61                     span_lint_and_sugg(
  62                         cx,
  63                         REPEAT_ONCE,
  64                         expr.span,
  65                         "calling `repeat(1)` on slice",
  66                         "consider using `.to_vec()` instead",
  67                         format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
  68                         Applicability::MachineApplicable,
  69                     );
  70                 } else if is_type_diagnostic_item(cx, ty, sym::string_type) {
  71                     span_lint_and_sugg(
  72                         cx,
  73                         REPEAT_ONCE,
  74                         expr.span,
  75                         "calling `repeat(1)` on a string literal",
  76                         "consider using `.clone()` instead",
  77                         format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
  78                         Applicability::MachineApplicable,
  79                     );
  80                 }
  81             }
  82         }
  83     }
  84 }