Add a suggestion and a note about orphan rules for from_over_into

clippy_lints/src/from_over_into.rs

@@ -1,11 +1,19 @@
-use clippy_utils::diagnostics::span_lint_and_help;
-use clippy_utils::{meets_msrv, msrvs};
-use if_chain::if_chain;
-use rustc_hir as hir;
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::macros::span_is_local;
+use clippy_utils::source::snippet_opt;
+use clippy_utils::{meets_msrv, msrvs, path_def_id};
+use rustc_errors::Applicability;
+use rustc_hir::intravisit::{walk_path, Visitor};
+use rustc_hir::{
+ GenericArg, GenericArgs, HirId, Impl, ImplItemKind, ImplItemRef, Item, ItemKind, PatKind, Path, PathSegment, Ty,
+ TyKind,
+};
 use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::hir::nested_filter::OnlyBodies;
 use rustc_semver::RustcVersion;
 use rustc_session::{declare_tool_lint, impl_lint_pass};
-use rustc_span::symbol::sym;
+use rustc_span::symbol::{kw, sym};
+use rustc_span::{Span, Symbol};
 
 declare_clippy_lint! {
  /// ### What it does
@@ -54,28 +62,152 @@ impl FromOverInto {
 impl_lint_pass!(FromOverInto => [FROM_OVER_INTO]);
 
 impl<'tcx> LateLintPass<'tcx> for FromOverInto {
- fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
- if !meets_msrv(self.msrv, msrvs::RE_REBALANCING_COHERENCE) {
+ fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
+ if !meets_msrv(self.msrv, msrvs::RE_REBALANCING_COHERENCE) || !span_is_local(item.span) {
  return;
  }
 
- if_chain! {
- if let hir::ItemKind::Impl{ .. } = &item.kind;
- if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
- if cx.tcx.is_diagnostic_item(sym::Into, impl_trait_ref.def_id);
-
- then {
- span_lint_and_help(
- cx,
- FROM_OVER_INTO,
- cx.tcx.sess.source_map().guess_head_span(item.span),
- "an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true",
- None,
- &format!("consider to implement `From<{}>` instead", impl_trait_ref.self_ty()),
- );
- }
+ if let ItemKind::Impl(Impl {
+ of_trait: Some(hir_trait_ref),
+ self_ty,
+ items: [impl_item_ref],
+ ..
+ }) = item.kind
+ && let Some(into_trait_seg) = hir_trait_ref.path.segments.last()
+ // `impl Into<target_ty> for self_ty`
+ && let Some(GenericArgs { args: [GenericArg::Type(target_ty)], .. }) = into_trait_seg.args
+ && let Some(middle_trait_ref) = cx.tcx.impl_trait_ref(item.def_id)
+ && cx.tcx.is_diagnostic_item(sym::Into, middle_trait_ref.def_id)
+ {
+ span_lint_and_then(
+ cx,
+ FROM_OVER_INTO,
+ cx.tcx.sess.source_map().guess_head_span(item.span),
+ "an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true",
+ |diag| {
+ // If the target type is likely foreign mention the orphan rules as it's a common source of confusion
+ if path_def_id(cx, target_ty.peel_refs()).map_or(true, |id| !id.is_local()) {
+ diag.help(
+ "`impl From<Local> for Foreign` is allowed by the orphan rules, for more information see\n\
+ https://doc.rust-lang.org/reference/items/implementations.html#trait-implementation-coherence"
+ );
+ }
+
+ let message = format!("replace the `Into` implentation with `From<{}>`", middle_trait_ref.self_ty());
+ if let Some(suggestions) = convert_to_from(cx, into_trait_seg, target_ty, self_ty, impl_item_ref) {
+ diag.multipart_suggestion(message, suggestions, Applicability::MachineApplicable);
+ } else {
+ diag.help(message);
+ }
+ },
+ );
  }
  }
 
  extract_msrv_attr!(LateContext);
 }
+
+/// Finds the occurences of `Self` and `self`
+struct SelfFinder<'a, 'tcx> {
+ cx: &'a LateContext<'tcx>,
+ /// Occurences of `Self`
+ upper: Vec<Span>,
+ /// Occurences of `self`
+ lower: Vec<Span>,
+ /// If any of the `self`/`Self` usages were from an expansion, or the body contained a binding
+ /// already named `val`
+ invalid: bool,
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for SelfFinder<'a, 'tcx> {
+ type NestedFilter = OnlyBodies;
+
+ fn nested_visit_map(&mut self) -> Self::Map {
+ self.cx.tcx.hir()
+ }
+
+ fn visit_path(&mut self, path: &'tcx Path<'tcx>, _id: HirId) {
+ for segment in path.segments {
+ match segment.ident.name {
+ kw::SelfLower => self.lower.push(segment.ident.span),
+ kw::SelfUpper => self.upper.push(segment.ident.span),
+ _ => continue,
+ }
+ }
+
+ self.invalid |= path.span.from_expansion();
+ if !self.invalid {
+ walk_path(self, path);
+ }
+ }
+
+ fn visit_name(&mut self, name: Symbol) {
+ if name == sym::val {
+ self.invalid = true;
+ }
+ }
+}
+
+fn convert_to_from(
+ cx: &LateContext<'_>,
+ into_trait_seg: &PathSegment<'_>,
+ target_ty: &Ty<'_>,
+ self_ty: &Ty<'_>,
+ impl_item_ref: &ImplItemRef,
+) -> Option<Vec<(Span, String)>> {
+ let impl_item = cx.tcx.hir().impl_item(impl_item_ref.id);
+ let ImplItemKind::Fn(ref sig, body_id) = impl_item.kind else { return None };
+ let body = cx.tcx.hir().body(body_id);
+ let [input] = body.params else { return None };
+ let PatKind::Binding(.., self_ident, None) = input.pat.kind else { return None };
+
+ let from = snippet_opt(cx, self_ty.span)?;
+ let into = snippet_opt(cx, target_ty.span)?;
+
+ let mut suggestions = vec![
+ // impl Into<T> for U -> impl From<T> for U
+ // ~~~~ ~~~~
+ (into_trait_seg.ident.span, String::from("From")),
+ // impl Into<T> for U -> impl Into<U> for U
+ // ~ ~
+ (target_ty.span, from.clone()),
+ // impl Into<T> for U -> impl Into<T> for T
+ // ~ ~
+ (self_ty.span, into),
+ // fn into(self) -> T -> fn from(self) -> T
+ // ~~~~ ~~~~
+ (impl_item.ident.span, String::from("from")),
+ // fn into([mut] self) -> T -> fn into([mut] v: T) -> T
+ // ~~~~ ~~~~
+ (self_ident.span, format!("val: {from}")),
+ // fn into(self) -> T -> fn into(self) -> Self
+ // ~ ~~~~
+ (sig.decl.output.span(), String::from("Self")),
+ ];
+
+ let mut finder = SelfFinder {
+ cx,
+ upper: Vec::new(),
+ lower: Vec::new(),
+ invalid: false,
+ };
+ finder.visit_expr(body.value);
+
+ if finder.invalid {
+ return None;
+ }
+
+ // don't try to replace e.g. `Self::default()` with `&[T]::default()`
+ if !finder.upper.is_empty() && !matches!(self_ty.kind, TyKind::Path(_)) {
+ return None;
+ }
+
+ for span in finder.upper {
+ suggestions.push((span, from.clone()));
+ }
+ for span in finder.lower {
+ suggestions.push((span, String::from("val")));
+ }
+
+ Some(suggestions)
+}

tests/ui/from_over_into.fixed

@@ -0,0 +1,62 @@
+// run-rustfix
+
+#![warn(clippy::from_over_into)]
+#![allow(unused)]
+
+// this should throw an error
+struct StringWrapper(String);
+
+impl From<String> for StringWrapper {
+ fn from(val: String) -> Self {
+ StringWrapper(val)
+ }
+}
+
+struct SelfType(String);
+
+impl From<String> for SelfType {
+ fn from(val: String) -> Self {
+ SelfType(String::new())
+ }
+}
+
+#[derive(Default)]
+struct X;
+
+impl X {
+ const FOO: &'static str = "a";
+}
+
+struct SelfKeywords;
+
+impl From<X> for SelfKeywords {
+ fn from(val: X) -> Self {
+ let _ = X::default();
+ let _ = X::FOO;
+ let _: X = val;
+
+ SelfKeywords
+ }
+}
+
+struct ExplicitPaths(bool);
+
+impl core::convert::From<crate::ExplicitPaths> for bool {
+ fn from(mut val: crate::ExplicitPaths) -> Self {
+ let in_closure = || val.0;
+
+ val.0 = false;
+ val.0
+ }
+}
+
+// this is fine
+struct A(String);
+
+impl From<String> for A {
+ fn from(s: String) -> A {
+ A(s)
+ }
+}
+
+fn main() {}

tests/ui/from_over_into.rs

@@ -1,4 +1,7 @@
+// run-rustfix
+
 #![warn(clippy::from_over_into)]
+#![allow(unused)]
 
 // this should throw an error
 struct StringWrapper(String);
@@ -9,6 +12,44 @@ impl Into<StringWrapper> for String {
  }
 }
 
+struct SelfType(String);
+
+impl Into<SelfType> for String {
+ fn into(self) -> SelfType {
+ SelfType(Self::new())
+ }
+}
+
+#[derive(Default)]
+struct X;
+
+impl X {
+ const FOO: &'static str = "a";
+}
+
+struct SelfKeywords;
+
+impl Into<SelfKeywords> for X {
+ fn into(self) -> SelfKeywords {
+ let _ = Self::default();
+ let _ = Self::FOO;
+ let _: Self = self;
+
+ SelfKeywords
+ }
+}
+
+struct ExplicitPaths(bool);
+
+impl core::convert::Into<bool> for crate::ExplicitPaths {
+ fn into(mut self) -> bool {
+ let in_closure = || self.0;
+
+ self.0 = false;
+ self.0
+ }
+}
+
 // this is fine
 struct A(String);
 

tests/ui/from_over_into.stderr

@@ -1,11 +1,62 @@
 error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
- --> $DIR/from_over_into.rs:6:1
+ --> $DIR/from_over_into.rs:9:1
  |
 LL | impl Into<StringWrapper> for String {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
- = help: consider to implement `From<std::string::String>` instead
  = note: `-D clippy::from-over-into` implied by `-D warnings`
+help: replace the `Into` implentation with `From<std::string::String>`
+ |
+LL ~ impl From<String> for StringWrapper {
+LL ~ fn from(val: String) -> Self {
+LL ~ StringWrapper(val)
+ |
+
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+ --> $DIR/from_over_into.rs:17:1
+ |
+LL | impl Into<SelfType> for String {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+help: replace the `Into` implentation with `From<std::string::String>`
+ |
+LL ~ impl From<String> for SelfType {
+LL ~ fn from(val: String) -> Self {
+LL ~ SelfType(String::new())
+ |
+
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+ --> $DIR/from_over_into.rs:32:1
+ |
+LL | impl Into<SelfKeywords> for X {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+help: replace the `Into` implentation with `From<X>`
+ |
+LL ~ impl From<X> for SelfKeywords {
+LL ~ fn from(val: X) -> Self {
+LL ~ let _ = X::default();
+LL ~ let _ = X::FOO;
+LL ~ let _: X = val;
+ |
+
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+ --> $DIR/from_over_into.rs:44:1
+ |
+LL | impl core::convert::Into<bool> for crate::ExplicitPaths {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = help: `impl From<Local> for Foreign` is allowed by the orphan rules, for more information see
+ https://doc.rust-lang.org/reference/items/implementations.html#trait-implementation-coherence
+help: replace the `Into` implentation with `From<ExplicitPaths>`
+ |
+LL ~ impl core::convert::From<crate::ExplicitPaths> for bool {
+LL ~ fn from(mut val: crate::ExplicitPaths) -> Self {
+LL ~ let in_closure = || val.0;
+LL | 
+LL ~ val.0 = false;
+LL ~ val.0
+ |
 
-error: aborting due to previous error
+error: aborting due to 4 previous errors