src/tools/clippy/clippy_lints/src/repeat_once.rs

   1 use crate::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     /// **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.
  20     ///
  21     /// **Known problems:** None.
  22     ///
  23     /// **Example:**
  24     ///
  25     /// ```rust
  26     /// fn main() {
  27     ///     let x = String::from("hello world").repeat(1);
  28     /// }
  29     /// ```
  30     /// Use instead:
  31     /// ```rust
  32     /// fn main() {
  33     ///     let x = String::from("hello world").clone();
  34     /// }
  35     /// ```
  36     pub REPEAT_ONCE,
  37     complexity,
  38     "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
  39 }
  40
  41 declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
  42
  43 impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
  44     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
  45         if_chain! {
  46             if let ExprKind::MethodCall(path, _, [receiver, count], _) = &expr.kind;
  47             if path.ident.name == sym!(repeat);
  48             if let Some(Constant::Int(1)) = constant_context(cx, cx.typeck_results()).expr(&count);
  49             if !in_macro(receiver.span);
  50             then {
  51                 let ty = cx.typeck_results().expr_ty(&receiver).peel_refs();
  52                 if ty.is_str() {
  53                     span_lint_and_sugg(
  54                         cx,
  55                         REPEAT_ONCE,
  56                         expr.span,
  57                         "calling `repeat(1)` on str",
  58                         "consider using `.to_string()` instead",
  59                         format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
  60                         Applicability::MachineApplicable,
  61                     );
  62                 } else if ty.builtin_index().is_some() {
  63                     span_lint_and_sugg(
  64                         cx,
  65                         REPEAT_ONCE,
  66                         expr.span,
  67                         "calling `repeat(1)` on slice",
  68                         "consider using `.to_vec()` instead",
  69                         format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
  70                         Applicability::MachineApplicable,
  71                     );
  72                 } else if is_type_diagnostic_item(cx, ty, sym::string_type) {
  73                     span_lint_and_sugg(
  74                         cx,
  75                         REPEAT_ONCE,
  76                         expr.span,
  77                         "calling `repeat(1)` on a string literal",
  78                         "consider using `.clone()` instead",
  79                         format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
  80                         Applicability::MachineApplicable,
  81                     );
  82                 }
  83             }
  84         }
  85     }
  86 }