1 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
2 use clippy_utils::source::{snippet, snippet_with_macro_callsite};
3 use clippy_utils::sugg::Sugg;
4 use clippy_utils::ty::{is_copy, is_type_diagnostic_item, same_type_and_consts};
5 use clippy_utils::{get_parent_expr, is_trait_method, match_def_path, path_to_local, paths};
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::{BindingAnnotation, Expr, ExprKind, HirId, MatchSource, Node, PatKind};
9 use rustc_lint::{LateContext, LateLintPass};
11 use rustc_session::{declare_tool_lint, impl_lint_pass};
14 declare_clippy_lint! {
16 /// Checks for `Into`, `TryInto`, `From`, `TryFrom`, or `IntoIter` calls
17 /// which uselessly convert to the same type.
19 /// ### Why is this bad?
24 /// // format!() returns a `String`
25 /// let s: String = format!("hello").into();
30 /// let s: String = format!("hello");
32 #[clippy::version = "1.45.0"]
33 pub USELESS_CONVERSION,
35 "calls to `Into`, `TryInto`, `From`, `TryFrom`, or `IntoIter` which perform useless conversions to the same type"
39 pub struct UselessConversion {
40 try_desugar_arm: Vec<HirId>,
43 impl_lint_pass!(UselessConversion => [USELESS_CONVERSION]);
45 #[expect(clippy::too_many_lines)]
46 impl<'tcx> LateLintPass<'tcx> for UselessConversion {
47 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
48 if e.span.from_expansion() {
52 if Some(&e.hir_id) == self.try_desugar_arm.last() {
57 ExprKind::Match(_, arms, MatchSource::TryDesugar) => {
58 let (ExprKind::Ret(Some(e)) | ExprKind::Break(_, Some(e))) = arms[0].body.kind else {
61 if let ExprKind::Call(_, [arg, ..]) = e.kind {
62 self.try_desugar_arm.push(arg.hir_id);
66 ExprKind::MethodCall(name, recv, ..) => {
67 if is_trait_method(cx, e, sym::Into) && name.ident.as_str() == "into" {
68 let a = cx.typeck_results().expr_ty(e);
69 let b = cx.typeck_results().expr_ty(recv);
70 if same_type_and_consts(a, b) {
71 let sugg = snippet_with_macro_callsite(cx, recv.span, "<expr>").to_string();
76 &format!("useless conversion to the same type: `{b}`"),
77 "consider removing `.into()`",
79 Applicability::MachineApplicable, // snippet
83 if is_trait_method(cx, e, sym::IntoIterator) && name.ident.name == sym::into_iter {
84 if get_parent_expr(cx, e).is_some() &&
85 let Some(id) = path_to_local(recv) &&
86 let Node::Pat(pat) = cx.tcx.hir().get(id) &&
87 let PatKind::Binding(ann, ..) = pat.kind &&
88 ann != BindingAnnotation::MUT
90 // Do not remove .into_iter() applied to a non-mutable local variable used in
91 // a larger expression context as it would differ in mutability.
95 let a = cx.typeck_results().expr_ty(e);
96 let b = cx.typeck_results().expr_ty(recv);
98 // If the types are identical then .into_iter() can be removed, unless the type
99 // implements Copy, in which case .into_iter() returns a copy of the receiver and
100 // cannot be safely omitted.
101 if same_type_and_consts(a, b) && !is_copy(cx, b) {
102 let sugg = snippet(cx, recv.span, "<expr>").into_owned();
107 &format!("useless conversion to the same type: `{b}`"),
108 "consider removing `.into_iter()`",
110 Applicability::MachineApplicable, // snippet
115 if is_trait_method(cx, e, sym::TryInto) && name.ident.name == sym::try_into;
116 let a = cx.typeck_results().expr_ty(e);
117 let b = cx.typeck_results().expr_ty(recv);
118 if is_type_diagnostic_item(cx, a, sym::Result);
119 if let ty::Adt(_, substs) = a.kind();
120 if let Some(a_type) = substs.types().next();
121 if same_type_and_consts(a_type, b);
128 &format!("useless conversion to the same type: `{b}`"),
130 "consider removing `.try_into()`",
136 ExprKind::Call(path, [arg]) => {
138 if let ExprKind::Path(ref qpath) = path.kind;
139 if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id();
141 let a = cx.typeck_results().expr_ty(e);
142 let b = cx.typeck_results().expr_ty(arg);
144 if match_def_path(cx, def_id, &paths::TRY_FROM);
145 if is_type_diagnostic_item(cx, a, sym::Result);
146 if let ty::Adt(_, substs) = a.kind();
147 if let Some(a_type) = substs.types().next();
148 if same_type_and_consts(a_type, b);
151 let hint = format!("consider removing `{}()`", snippet(cx, path.span, "TryFrom::try_from"));
156 &format!("useless conversion to the same type: `{b}`"),
164 if Some(def_id) == cx.tcx.lang_items().from_fn();
165 if same_type_and_consts(a, b);
168 let sugg = Sugg::hir_with_macro_callsite(cx, arg, "<expr>").maybe_par();
170 format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
175 &format!("useless conversion to the same type: `{b}`"),
178 Applicability::MachineApplicable, // snippet
190 fn check_expr_post(&mut self, _: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
191 if Some(&e.hir_id) == self.try_desugar_arm.last() {
192 self.try_desugar_arm.pop();