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use clippy_utils::consts::{constant_context, Constant};
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::in_macro;
use clippy_utils::source::snippet;
use clippy_utils::ty::is_type_diagnostic_item;
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// **What it does:** Checks for usage of `.repeat(1)` and suggest the following method for each types.
/// - `.to_string()` for `str`
/// - `.clone()` for `String`
/// - `.to_vec()` for `slice`
///
/// The lint will evaluate constant expressions and values as arguments of `.repeat(..)` and emit a message if
/// they are equivalent to `1`. (Related discussion in [rust-clippy#7306](https://github.com/rust-lang/rust-clippy/issues/7306))
///
/// **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.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// fn main() {
/// let x = String::from("hello world").repeat(1);
/// }
/// ```
/// Use instead:
/// ```rust
/// fn main() {
/// let x = String::from("hello world").clone();
/// }
/// ```
pub REPEAT_ONCE,
complexity,
"using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
}
declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
if_chain! {
if let ExprKind::MethodCall(path, _, [receiver, count], _) = &expr.kind;
if path.ident.name == sym!(repeat);
if let Some(Constant::Int(1)) = constant_context(cx, cx.typeck_results()).expr(count);
if !in_macro(receiver.span);
then {
let ty = cx.typeck_results().expr_ty(receiver).peel_refs();
if ty.is_str() {
span_lint_and_sugg(
cx,
REPEAT_ONCE,
expr.span,
"calling `repeat(1)` on str",
"consider using `.to_string()` instead",
format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
Applicability::MachineApplicable,
);
} else if ty.builtin_index().is_some() {
span_lint_and_sugg(
cx,
REPEAT_ONCE,
expr.span,
"calling `repeat(1)` on slice",
"consider using `.to_vec()` instead",
format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
Applicability::MachineApplicable,
);
} else if is_type_diagnostic_item(cx, ty, sym::string_type) {
span_lint_and_sugg(
cx,
REPEAT_ONCE,
expr.span,
"calling `repeat(1)` on a string literal",
"consider using `.clone()` instead",
format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
Applicability::MachineApplicable,
);
}
}
}
}
}
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