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