-use clippy_utils::{diagnostics::span_lint_and_help, is_default_equivalent, path_def_id};
-use rustc_hir::{Expr, ExprKind, QPath};
+use clippy_utils::{
+ diagnostics::span_lint_and_sugg, get_parent_node, is_default_equivalent, macros::macro_backtrace, match_path,
+ path_def_id, paths, ty::expr_sig,
+};
+use rustc_errors::Applicability;
+use rustc_hir::{
+ intravisit::{walk_ty, Visitor},
+ Block, Expr, ExprKind, Local, Node, QPath, TyKind,
+};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
/// Second, `Box::default()` can be faster
/// [in certain cases](https://nnethercote.github.io/perf-book/standard-library-types.html#box).
///
- /// ### Known problems
- /// The lint may miss some cases (e.g. Box::new(String::from(""))).
- /// On the other hand, it will trigger on cases where the `default`
- /// code comes from a macro that does something different based on
- /// e.g. target operating system.
- ///
/// ### Example
/// ```rust
/// let x: Box<String> = Box::new(Default::default());
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
if let ExprKind::Call(box_new, [arg]) = expr.kind
&& let ExprKind::Path(QPath::TypeRelative(ty, seg)) = box_new.kind
- && let ExprKind::Call(..) = arg.kind
+ && let ExprKind::Call(arg_path, ..) = arg.kind
&& !in_external_macro(cx.sess(), expr.span)
- && expr.span.eq_ctxt(arg.span)
+ && (expr.span.eq_ctxt(arg.span) || is_vec_expn(cx, arg))
&& seg.ident.name == sym::new
- && path_def_id(cx, ty) == cx.tcx.lang_items().owned_box()
+ && path_def_id(cx, ty).map_or(false, |id| Some(id) == cx.tcx.lang_items().owned_box())
&& is_default_equivalent(cx, arg)
{
- span_lint_and_help(
+ let arg_ty = cx.typeck_results().expr_ty(arg);
+ span_lint_and_sugg(
cx,
BOX_DEFAULT,
expr.span,
"`Box::new(_)` of default value",
- None,
- "use `Box::default()` instead",
+ "try",
+ if is_plain_default(arg_path) || given_type(cx, expr) {
+ "Box::default()".into()
+ } else {
+ format!("Box::<{arg_ty}>::default()")
+ },
+ Applicability::MachineApplicable
);
}
}
}
+
+fn is_plain_default(arg_path: &Expr<'_>) -> bool {
+ // we need to match the actual path so we don't match e.g. "u8::default"
+ if let ExprKind::Path(QPath::Resolved(None, path)) = &arg_path.kind {
+ // avoid generic parameters
+ match_path(path, &paths::DEFAULT_TRAIT_METHOD) && path.segments.iter().all(|seg| seg.args.is_none())
+ } else {
+ false
+ }
+}
+
+fn is_vec_expn(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+ macro_backtrace(expr.span)
+ .next()
+ .map_or(false, |call| cx.tcx.is_diagnostic_item(sym::vec_macro, call.def_id))
+}
+
+#[derive(Default)]
+struct InferVisitor(bool);
+
+impl<'tcx> Visitor<'tcx> for InferVisitor {
+ fn visit_ty(&mut self, t: &rustc_hir::Ty<'_>) {
+ self.0 |= matches!(t.kind, TyKind::Infer | TyKind::OpaqueDef(..) | TyKind::TraitObject(..));
+ if !self.0 {
+ walk_ty(self, t);
+ }
+ }
+}
+
+fn given_type(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+ match get_parent_node(cx.tcx, expr.hir_id) {
+ Some(Node::Local(Local { ty: Some(ty), .. })) => {
+ let mut v = InferVisitor::default();
+ v.visit_ty(ty);
+ !v.0
+ },
+ Some(
+ Node::Expr(Expr {
+ kind: ExprKind::Call(path, args),
+ ..
+ }) | Node::Block(Block {
+ expr:
+ Some(Expr {
+ kind: ExprKind::Call(path, args),
+ ..
+ }),
+ ..
+ }),
+ ) => {
+ if let Some(index) = args.iter().position(|arg| arg.hir_id == expr.hir_id) &&
+ let Some(sig) = expr_sig(cx, path) &&
+ let Some(input) = sig.input(index)
+ {
+ input.no_bound_vars().is_some()
+ } else {
+ false
+ }
+ },
+ _ => false,
+ }
+}