1 use crate::utils::sugg::Sugg;
3 get_parent_expr, match_def_path, match_trait_method, paths, snippet, snippet_with_macro_callsite,
4 span_lint_and_help, span_lint_and_sugg,
6 use clippy_utils::ty::is_type_diagnostic_item;
7 use if_chain::if_chain;
8 use rustc_errors::Applicability;
9 use rustc_hir::{Expr, ExprKind, HirId, MatchSource};
10 use rustc_lint::{LateContext, LateLintPass};
11 use rustc_middle::ty::{self, TyS};
12 use rustc_session::{declare_tool_lint, impl_lint_pass};
15 declare_clippy_lint! {
16 /// **What it does:** Checks for `Into`, `TryInto`, `From`, `TryFrom`, or `IntoIter` calls
17 /// which uselessly convert to the same type.
19 /// **Why is this bad?** Redundant code.
21 /// **Known problems:** None.
27 /// // format!() returns a `String`
28 /// let s: String = format!("hello").into();
31 /// let s: String = format!("hello");
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 #[allow(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(_, ref arms, MatchSource::TryDesugar) => {
58 let e = match arms[0].body.kind {
59 ExprKind::Ret(Some(ref e)) | ExprKind::Break(_, Some(ref e)) => e,
62 if let ExprKind::Call(_, ref args) = e.kind {
63 self.try_desugar_arm.push(args[0].hir_id);
67 ExprKind::MethodCall(ref name, .., ref args, _) => {
68 if match_trait_method(cx, e, &paths::INTO) && &*name.ident.as_str() == "into" {
69 let a = cx.typeck_results().expr_ty(e);
70 let b = cx.typeck_results().expr_ty(&args[0]);
71 if TyS::same_type(a, b) {
72 let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
77 &format!("useless conversion to the same type: `{}`", b),
78 "consider removing `.into()`",
80 Applicability::MachineApplicable, // snippet
84 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && name.ident.name == sym::into_iter {
85 if let Some(parent_expr) = get_parent_expr(cx, e) {
86 if let ExprKind::MethodCall(ref parent_name, ..) = parent_expr.kind {
87 if parent_name.ident.name != sym::into_iter {
92 let a = cx.typeck_results().expr_ty(e);
93 let b = cx.typeck_results().expr_ty(&args[0]);
94 if TyS::same_type(a, b) {
95 let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
100 &format!("useless conversion to the same type: `{}`", b),
101 "consider removing `.into_iter()`",
103 Applicability::MachineApplicable, // snippet
107 if match_trait_method(cx, e, &paths::TRY_INTO_TRAIT) && &*name.ident.as_str() == "try_into" {
109 let a = cx.typeck_results().expr_ty(e);
110 let b = cx.typeck_results().expr_ty(&args[0]);
111 if is_type_diagnostic_item(cx, a, sym::result_type);
112 if let ty::Adt(_, substs) = a.kind();
113 if let Some(a_type) = substs.types().next();
114 if TyS::same_type(a_type, b);
121 &format!("useless conversion to the same type: `{}`", b),
123 "consider removing `.try_into()`",
130 ExprKind::Call(ref path, ref args) => {
133 if let ExprKind::Path(ref qpath) = path.kind;
134 if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id();
135 let a = cx.typeck_results().expr_ty(e);
136 let b = cx.typeck_results().expr_ty(&args[0]);
140 if match_def_path(cx, def_id, &paths::TRY_FROM);
141 if is_type_diagnostic_item(cx, a, sym::result_type);
142 if let ty::Adt(_, substs) = a.kind();
143 if let Some(a_type) = substs.types().next();
144 if TyS::same_type(a_type, b);
147 let hint = format!("consider removing `{}()`", snippet(cx, path.span, "TryFrom::try_from"));
152 &format!("useless conversion to the same type: `{}`", b),
160 if match_def_path(cx, def_id, &paths::FROM_FROM);
161 if TyS::same_type(a, b);
164 let sugg = Sugg::hir_with_macro_callsite(cx, &args[0], "<expr>").maybe_par();
166 format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
171 &format!("useless conversion to the same type: `{}`", b),
174 Applicability::MachineApplicable, // snippet
186 fn check_expr_post(&mut self, _: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
187 if Some(&e.hir_id) == self.try_desugar_arm.last() {
188 self.try_desugar_arm.pop();