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

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