1 use crate::utils::sugg::Sugg;
3 get_parent_expr, is_type_diagnostic_item, match_def_path, match_trait_method, paths, snippet,
4 snippet_with_macro_callsite, span_lint_and_help, span_lint_and_sugg,
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::{Expr, ExprKind, HirId, MatchSource};
9 use rustc_lint::{LateContext, LateLintPass};
10 use rustc_middle::ty::{self, TyS};
11 use rustc_session::{declare_tool_lint, impl_lint_pass};
14 declare_clippy_lint! {
15 /// **What it does:** Checks for `Into`, `TryInto`, `From`, `TryFrom`, or `IntoIter` calls
16 /// which uselessly convert to the same type.
18 /// **Why is this bad?** Redundant code.
20 /// **Known problems:** None.
26 /// // format!() returns a `String`
27 /// let s: String = format!("hello").into();
30 /// let s: String = format!("hello");
32 pub USELESS_CONVERSION,
34 "calls to `Into`, `TryInto`, `From`, `TryFrom`, or `IntoIter` which perform useless conversions to the same type"
38 pub struct UselessConversion {
39 try_desugar_arm: Vec<HirId>,
42 impl_lint_pass!(UselessConversion => [USELESS_CONVERSION]);
44 #[allow(clippy::too_many_lines)]
45 impl<'tcx> LateLintPass<'tcx> for UselessConversion {
46 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
47 if e.span.from_expansion() {
51 if Some(&e.hir_id) == self.try_desugar_arm.last() {
56 ExprKind::Match(_, ref arms, MatchSource::TryDesugar) => {
57 let e = match arms[0].body.kind {
58 ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
61 if let ExprKind::Call(_, ref args) = e.kind {
62 self.try_desugar_arm.push(args[0].hir_id);
66 ExprKind::MethodCall(ref name, .., ref args, _) => {
67 if match_trait_method(cx, e, &paths::INTO) && &*name.ident.as_str() == "into" {
68 let a = cx.typeck_results().expr_ty(e);
69 let b = cx.typeck_results().expr_ty(&args[0]);
70 if TyS::same_type(a, b) {
71 let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
76 &format!("useless conversion to the same type: `{}`", b),
77 "consider removing `.into()`",
79 Applicability::MachineApplicable, // snippet
83 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && name.ident.name == sym::into_iter {
84 if let Some(parent_expr) = get_parent_expr(cx, e) {
85 if let ExprKind::MethodCall(ref parent_name, ..) = parent_expr.kind {
86 if parent_name.ident.name != sym::into_iter {
91 let a = cx.typeck_results().expr_ty(e);
92 let b = cx.typeck_results().expr_ty(&args[0]);
93 if TyS::same_type(a, b) {
94 let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
99 &format!("useless conversion to the same type: `{}`", b),
100 "consider removing `.into_iter()`",
102 Applicability::MachineApplicable, // snippet
106 if match_trait_method(cx, e, &paths::TRY_INTO_TRAIT) && &*name.ident.as_str() == "try_into" {
108 let a = cx.typeck_results().expr_ty(e);
109 let b = cx.typeck_results().expr_ty(&args[0]);
110 if is_type_diagnostic_item(cx, a, sym::result_type);
111 if let ty::Adt(_, substs) = a.kind();
112 if let Some(a_type) = substs.types().next();
113 if TyS::same_type(a_type, b);
120 &format!("useless conversion to the same type: `{}`", b),
122 "consider removing `.try_into()`",
129 ExprKind::Call(ref path, ref args) => {
132 if let ExprKind::Path(ref qpath) = path.kind;
133 if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id();
134 let a = cx.typeck_results().expr_ty(e);
135 let b = cx.typeck_results().expr_ty(&args[0]);
139 if match_def_path(cx, def_id, &paths::TRY_FROM);
140 if is_type_diagnostic_item(cx, a, sym::result_type);
141 if let ty::Adt(_, substs) = a.kind();
142 if let Some(a_type) = substs.types().next();
143 if TyS::same_type(a_type, b);
146 let hint = format!("consider removing `{}()`", snippet(cx, path.span, "TryFrom::try_from"));
151 &format!("useless conversion to the same type: `{}`", b),
159 if match_def_path(cx, def_id, &paths::FROM_FROM);
160 if TyS::same_type(a, b);
163 let sugg = Sugg::hir_with_macro_callsite(cx, &args[0], "<expr>").maybe_par();
165 format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
170 &format!("useless conversion to the same type: `{}`", b),
173 Applicability::MachineApplicable, // snippet
185 fn check_expr_post(&mut self, _: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
186 if Some(&e.hir_id) == self.try_desugar_arm.last() {
187 self.try_desugar_arm.pop();