1 use clippy_utils::diagnostics::span_lint_and_help;
2 use clippy_utils::paths::INTO;
3 use clippy_utils::{match_def_path, meets_msrv};
4 use if_chain::if_chain;
6 use rustc_lint::{LateContext, LateLintPass, LintContext};
7 use rustc_semver::RustcVersion;
8 use rustc_session::{declare_tool_lint, impl_lint_pass};
10 const FROM_OVER_INTO_MSRV: RustcVersion = RustcVersion::new(1, 41, 0);
12 declare_clippy_lint! {
13 /// **What it does:** Searches for implementations of the `Into<..>` trait and suggests to implement `From<..>` instead.
15 /// **Why is this bad?** According the std docs implementing `From<..>` is preferred since it gives you `Into<..>` for free where the reverse isn't true.
17 /// **Known problems:** None.
22 /// struct StringWrapper(String);
24 /// impl Into<StringWrapper> for String {
25 /// fn into(self) -> StringWrapper {
26 /// StringWrapper(self)
32 /// struct StringWrapper(String);
34 /// impl From<String> for StringWrapper {
35 /// fn from(s: String) -> StringWrapper {
42 "Warns on implementations of `Into<..>` to use `From<..>`"
45 pub struct FromOverInto {
46 msrv: Option<RustcVersion>,
51 pub fn new(msrv: Option<RustcVersion>) -> Self {
56 impl_lint_pass!(FromOverInto => [FROM_OVER_INTO]);
58 impl LateLintPass<'_> for FromOverInto {
59 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
60 if !meets_msrv(self.msrv.as_ref(), &FROM_OVER_INTO_MSRV) {
65 if let hir::ItemKind::Impl{ .. } = &item.kind;
66 if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
67 if match_def_path(cx, impl_trait_ref.def_id, &INTO);
73 cx.tcx.sess.source_map().guess_head_span(item.span),
74 "an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true",
76 &format!("consider to implement `From<{}>` instead", impl_trait_ref.self_ty()),
82 extract_msrv_attr!(LateContext);