Move RepeatOnce into Methods lint pass

Author: Jarcho

clippy_lints/src/lib.register_all.rs

@@ -197,6 +197,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(methods::OR_FUN_CALL),
     LintId::of(methods::OR_THEN_UNWRAP),
     LintId::of(methods::RANGE_ZIP_WITH_LEN),
+    LintId::of(methods::REPEAT_ONCE),
     LintId::of(methods::RESULT_MAP_OR_INTO_OPTION),
     LintId::of(methods::SEARCH_IS_SOME),
     LintId::of(methods::SHOULD_IMPLEMENT_TRAIT),
@@ -287,7 +288,6 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(redundant_static_lifetimes::REDUNDANT_STATIC_LIFETIMES),
     LintId::of(reference::DEREF_ADDROF),
     LintId::of(regex::INVALID_REGEX),
-    LintId::of(repeat_once::REPEAT_ONCE),
     LintId::of(returns::LET_AND_RETURN),
     LintId::of(returns::NEEDLESS_RETURN),
     LintId::of(self_named_constructors::SELF_NAMED_CONSTRUCTORS),

clippy_lints/src/lib.register_complexity.rs

@@ -52,6 +52,7 @@ store.register_group(true, "clippy::complexity", Some("clippy_complexity"), vec!
     LintId::of(methods::OPTION_FILTER_MAP),
     LintId::of(methods::OR_THEN_UNWRAP),
     LintId::of(methods::RANGE_ZIP_WITH_LEN),
+    LintId::of(methods::REPEAT_ONCE),
     LintId::of(methods::SEARCH_IS_SOME),
     LintId::of(methods::SKIP_WHILE_NEXT),
     LintId::of(methods::UNNECESSARY_FILTER_MAP),
@@ -80,7 +81,6 @@ store.register_group(true, "clippy::complexity", Some("clippy_complexity"), vec!
     LintId::of(redundant_closure_call::REDUNDANT_CLOSURE_CALL),
     LintId::of(redundant_slicing::REDUNDANT_SLICING),
     LintId::of(reference::DEREF_ADDROF),
-    LintId::of(repeat_once::REPEAT_ONCE),
     LintId::of(strings::STRING_FROM_UTF8_AS_BYTES),
     LintId::of(strlen_on_c_strings::STRLEN_ON_C_STRINGS),
     LintId::of(swap::MANUAL_SWAP),

clippy_lints/src/lib.register_lints.rs

@@ -346,6 +346,7 @@ store.register_lints(&[
     methods::OR_THEN_UNWRAP,
     methods::PATH_BUF_PUSH_OVERWRITE,
     methods::RANGE_ZIP_WITH_LEN,
+    methods::REPEAT_ONCE,
     methods::RESULT_MAP_OR_INTO_OPTION,
     methods::SEARCH_IS_SOME,
     methods::SHOULD_IMPLEMENT_TRAIT,
@@ -489,7 +490,6 @@ store.register_lints(&[
     reference::DEREF_ADDROF,
     regex::INVALID_REGEX,
     regex::TRIVIAL_REGEX,
-    repeat_once::REPEAT_ONCE,
     return_self_not_must_use::RETURN_SELF_NOT_MUST_USE,
     returns::LET_AND_RETURN,
     returns::NEEDLESS_RETURN,

clippy_lints/src/lib.rs

@@ -343,7 +343,6 @@ mod redundant_static_lifetimes;
 mod ref_option_ref;
 mod reference;
 mod regex;
-mod repeat_once;
 mod return_self_not_must_use;
 mod returns;
 mod same_name_method;
@@ -824,7 +823,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| Box::new(macro_use::MacroUseImports::default()));
     store.register_late_pass(|| Box::new(pattern_type_mismatch::PatternTypeMismatch));
     store.register_late_pass(|| Box::new(stable_sort_primitive::StableSortPrimitive));
-    store.register_late_pass(|| Box::new(repeat_once::RepeatOnce));
     store.register_late_pass(|| Box::new(unwrap_in_result::UnwrapInResult));
     store.register_late_pass(|| Box::new(semicolon_if_nothing_returned::SemicolonIfNothingReturned));
     store.register_late_pass(|| Box::new(async_yields_async::AsyncYieldsAsync));

clippy_lints/src/methods/mod.rs

@@ -65,6 +65,7 @@ mod or_fun_call;
 mod or_then_unwrap;
 mod path_buf_push_overwrite;
 mod range_zip_with_len;
+mod repeat_once;
 mod search_is_some;
 mod single_char_add_str;
 mod single_char_insert_string;
@@ -2760,6 +2761,38 @@ declare_clippy_lint! {
     "zipping iterator with a range when `enumerate()` would do"
 }
 
+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.
+    ///
+    /// ### Example
+    /// ```rust
+    /// fn main() {
+    ///     let x = String::from("hello world").repeat(1);
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// fn main() {
+    ///     let x = String::from("hello world").clone();
+    /// }
+    /// ```
+    #[clippy::version = "1.47.0"]
+    pub REPEAT_ONCE,
+    complexity,
+    "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Option<RustcVersion>,
@@ -2875,6 +2908,7 @@ impl_lint_pass!(Methods => [
     NONSENSICAL_OPEN_OPTIONS,
     PATH_BUF_PUSH_OVERWRITE,
     RANGE_ZIP_WITH_LEN,
+    REPEAT_ONCE,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -3263,6 +3297,9 @@ impl Methods {
                 ("push", [arg]) => {
                     path_buf_push_overwrite::check(cx, expr, arg);
                 },
+                ("repeat", [arg]) => {
+                    repeat_once::check(cx, expr, recv, arg);
+                },
                 ("splitn" | "rsplitn", [count_arg, pat_arg]) => {
                     if let Some((Constant::Int(count), _)) = constant(cx, cx.typeck_results(), count_arg) {
                         suspicious_splitn::check(cx, name, expr, recv, count);

clippy_lints/src/methods/repeat_once.rs

@@ -0,0 +1,52 @@
+use clippy_utils::consts::{constant_context, Constant};
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet;
+use clippy_utils::ty::is_type_diagnostic_item;
+use rustc_errors::Applicability;
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_span::sym;
+
+use super::REPEAT_ONCE;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    recv: &'tcx Expr<'_>,
+    repeat_arg: &'tcx Expr<'_>,
+) {
+    if constant_context(cx, cx.typeck_results()).expr(repeat_arg) == Some(Constant::Int(1)) {
+        let ty = cx.typeck_results().expr_ty(recv).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, recv.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, recv.span, r#""...""#)),
+                Applicability::MachineApplicable,
+            );
+        } else if is_type_diagnostic_item(cx, ty, sym::String) {
+            span_lint_and_sugg(
+                cx,
+                REPEAT_ONCE,
+                expr.span,
+                "calling `repeat(1)` on a string literal",
+                "consider using `.clone()` instead",
+                format!("{}.clone()", snippet(cx, recv.span, r#""...""#)),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+}