1 files changed, 139 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/rc_clone_in_vec_init.rs b/src/tools/clippy/clippy_lints/src/rc_clone_in_vec_init.rs
new file mode 100644
index 000000000..8db8c4e9b
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/rc_clone_in_vec_init.rs
@@ -0,0 +1,139 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::higher::VecArgs;
+use clippy_utils::last_path_segment;
+use clippy_utils::macros::root_macro_call_first_node;
+use clippy_utils::paths;
+use clippy_utils::source::{indent_of, snippet};
+use clippy_utils::ty::match_type;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, QPath, TyKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::{sym, Span, Symbol};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for reference-counted pointers (`Arc`, `Rc`, `rc::Weak`, and `sync::Weak`)
+    /// in `vec![elem; len]`
+    ///
+    /// ### Why is this bad?
+    /// This will create `elem` once and clone it `len` times - doing so with `Arc`/`Rc`/`Weak`
+    /// is a bit misleading, as it will create references to the same pointer, rather
+    /// than different instances.
+    ///
+    /// ### Example
+    /// ```rust
+    /// let v = vec![std::sync::Arc::new("some data".to_string()); 100];
+    /// // or
+    /// let v = vec![std::rc::Rc::new("some data".to_string()); 100];
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// // Initialize each value separately:
+    /// let mut data = Vec::with_capacity(100);
+    /// for _ in 0..100 {
+    ///     data.push(std::rc::Rc::new("some data".to_string()));
+    /// }
+    ///
+    /// // Or if you want clones of the same reference,
+    /// // Create the reference beforehand to clarify that
+    /// // it should be cloned for each value
+    /// let data = std::rc::Rc::new("some data".to_string());
+    /// let v = vec![data; 100];
+    /// ```
+    #[clippy::version = "1.62.0"]
+    pub RC_CLONE_IN_VEC_INIT,
+    suspicious,
+    "initializing reference-counted pointer in `vec![elem; len]`"
+}
+declare_lint_pass!(RcCloneInVecInit => [RC_CLONE_IN_VEC_INIT]);
+
+impl LateLintPass<'_> for RcCloneInVecInit {
+    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
+        let Some(macro_call) = root_macro_call_first_node(cx, expr) else { return; };
+        let Some(VecArgs::Repeat(elem, len)) = VecArgs::hir(cx, expr) else { return; };
+        let Some((symbol, func_span)) = ref_init(cx, elem) else { return; };
+
+        emit_lint(cx, symbol, macro_call.span, elem, len, func_span);
+    }
+}
+
+fn loop_init_suggestion(elem: &str, len: &str, indent: &str) -> String {
+    format!(
+        r#"{{
+{indent}    let mut v = Vec::with_capacity({len});
+{indent}    (0..{len}).for_each(|_| v.push({elem}));
+{indent}    v
+{indent}}}"#
+    )
+}
+
+fn extract_suggestion(elem: &str, len: &str, indent: &str) -> String {
+    format!(
+        "{{
+{indent}    let data = {elem};
+{indent}    vec![data; {len}]
+{indent}}}"
+    )
+}
+
+fn emit_lint(cx: &LateContext<'_>, symbol: Symbol, lint_span: Span, elem: &Expr<'_>, len: &Expr<'_>, func_span: Span) {
+    let symbol_name = symbol.as_str();
+
+    span_lint_and_then(
+        cx,
+        RC_CLONE_IN_VEC_INIT,
+        lint_span,
+        "initializing a reference-counted pointer in `vec![elem; len]`",
+        |diag| {
+            let len_snippet = snippet(cx, len.span, "..");
+            let elem_snippet = format!("{}(..)", snippet(cx, elem.span.with_hi(func_span.hi()), ".."));
+            let indentation = " ".repeat(indent_of(cx, lint_span).unwrap_or(0));
+            let loop_init_suggestion = loop_init_suggestion(&elem_snippet, len_snippet.as_ref(), &indentation);
+            let extract_suggestion = extract_suggestion(&elem_snippet, len_snippet.as_ref(), &indentation);
+
+            diag.note(format!("each element will point to the same `{symbol_name}` instance"));
+            diag.span_suggestion(
+                lint_span,
+                format!("consider initializing each `{symbol_name}` element individually"),
+                loop_init_suggestion,
+                Applicability::HasPlaceholders,
+            );
+            diag.span_suggestion(
+                lint_span,
+                format!(
+                    "or if this is intentional, consider extracting the `{symbol_name}` initialization to a variable"
+                ),
+                extract_suggestion,
+                Applicability::HasPlaceholders,
+            );
+        },
+    );
+}
+
+/// Checks whether the given `expr` is a call to `Arc::new`, `Rc::new`, or evaluates to a `Weak`
+fn ref_init(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<(Symbol, Span)> {
+    if_chain! {
+        if let ExprKind::Call(func, _args) = expr.kind;
+        if let ExprKind::Path(ref func_path @ QPath::TypeRelative(ty, _)) = func.kind;
+        if let TyKind::Path(ref ty_path) = ty.kind;
+        if let Some(def_id) = cx.qpath_res(ty_path, ty.hir_id).opt_def_id();
+
+        then {
+            if last_path_segment(func_path).ident.name == sym::new
+                && let Some(symbol) = cx
+                    .tcx
+                    .get_diagnostic_name(def_id)
+                    .filter(|symbol| symbol == &sym::Arc || symbol == &sym::Rc) {
+                return Some((symbol, func.span));
+            }
+
+            let ty_path = cx.typeck_results().expr_ty(expr);
+            if match_type(cx, ty_path, &paths::WEAK_RC) || match_type(cx, ty_path, &paths::WEAK_ARC) {
+                return Some((Symbol::intern("Weak"), func.span));
+            }
+        }
+    }
+
+    None
+}