src/tools/clippy/clippy_lints/src/from_over_into.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::{meets_msrv, msrvs};
   3 use if_chain::if_chain;
   4 use rustc_hir as hir;
   5 use rustc_lint::{LateContext, LateLintPass, LintContext};
   6 use rustc_semver::RustcVersion;
   7 use rustc_session::{declare_tool_lint, impl_lint_pass};
   8 use rustc_span::symbol::sym;
   9
  10 declare_clippy_lint! {
  11     /// ### What it does
  12     /// Searches for implementations of the `Into<..>` trait and suggests to implement `From<..>` instead.
  13     ///
  14     /// ### Why is this bad?
  15     /// According the std docs implementing `From<..>` is preferred since it gives you `Into<..>` for free where the reverse isn't true.
  16     ///
  17     /// ### Example
  18     /// ```rust
  19     /// struct StringWrapper(String);
  20     ///
  21     /// impl Into<StringWrapper> for String {
  22     ///     fn into(self) -> StringWrapper {
  23     ///         StringWrapper(self)
  24     ///     }
  25     /// }
  26     /// ```
  27     /// Use instead:
  28     /// ```rust
  29     /// struct StringWrapper(String);
  30     ///
  31     /// impl From<String> for StringWrapper {
  32     ///     fn from(s: String) -> StringWrapper {
  33     ///         StringWrapper(s)
  34     ///     }
  35     /// }
  36     /// ```
  37     pub FROM_OVER_INTO,
  38     style,
  39     "Warns on implementations of `Into<..>` to use `From<..>`"
  40 }
  41
  42 pub struct FromOverInto {
  43     msrv: Option<RustcVersion>,
  44 }
  45
  46 impl FromOverInto {
  47     #[must_use]
  48     pub fn new(msrv: Option<RustcVersion>) -> Self {
  49         FromOverInto { msrv }
  50     }
  51 }
  52
  53 impl_lint_pass!(FromOverInto => [FROM_OVER_INTO]);
  54
  55 impl LateLintPass<'_> for FromOverInto {
  56     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
  57         if !meets_msrv(self.msrv.as_ref(), &msrvs::RE_REBALANCING_COHERENCE) {
  58             return;
  59         }
  60
  61         if_chain! {
  62             if let hir::ItemKind::Impl{ .. } = &item.kind;
  63             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
  64             if cx.tcx.is_diagnostic_item(sym::into_trait, impl_trait_ref.def_id);
  65
  66             then {
  67                 span_lint_and_help(
  68                     cx,
  69                     FROM_OVER_INTO,
  70                     cx.tcx.sess.source_map().guess_head_span(item.span),
  71                     "an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true",
  72                     None,
  73                     &format!("consider to implement `From<{}>` instead", impl_trait_ref.self_ty()),
  74                 );
  75             }
  76         }
  77     }
  78
  79     extract_msrv_attr!(LateContext);
  80 }