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|
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 = "1.63.0"]
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
}
|
