Don't lint from_over_into for opaque types

Author: Jarcho

clippy_lints/src/from_over_into.rs

@@ -10,7 +10,7 @@ use rustc_hir::{
     TyKind,
 };
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::hir::nested_filter::OnlyBodies;
+use rustc_middle::{hir::nested_filter::OnlyBodies, ty};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::symbol::{kw, sym};
 use rustc_span::{Span, Symbol};
@@ -78,6 +78,7 @@ impl<'tcx> LateLintPass<'tcx> for FromOverInto {
             && let Some(GenericArgs { args: [GenericArg::Type(target_ty)], .. }) = into_trait_seg.args
             && let Some(middle_trait_ref) = cx.tcx.impl_trait_ref(item.owner_id)
             && cx.tcx.is_diagnostic_item(sym::Into, middle_trait_ref.def_id)
+            && !matches!(middle_trait_ref.substs.type_at(1).kind(), ty::Opaque(..))
         {
             span_lint_and_then(
                 cx,

tests/ui/from_over_into.fixed

@@ -1,5 +1,6 @@
 // run-rustfix
 
+#![feature(type_alias_impl_trait)]
 #![warn(clippy::from_over_into)]
 #![allow(unused)]
 
@@ -81,4 +82,10 @@ fn msrv_1_41() {
     }
 }
 
+type Opaque = impl Sized;
+struct IntoOpaque;
+impl Into<Opaque> for IntoOpaque {
+    fn into(self) -> Opaque {}
+}
+
 fn main() {}

tests/ui/from_over_into.rs

@@ -1,5 +1,6 @@
 // run-rustfix
 
+#![feature(type_alias_impl_trait)]
 #![warn(clippy::from_over_into)]
 #![allow(unused)]
 
@@ -81,4 +82,10 @@ fn msrv_1_41() {
     }
 }
 
+type Opaque = impl Sized;
+struct IntoOpaque;
+impl Into<Opaque> for IntoOpaque {
+    fn into(self) -> Opaque {}
+}
+
 fn main() {}

tests/ui/from_over_into.stderr

@@ -1,5 +1,5 @@
 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:9:1
+  --> $DIR/from_over_into.rs:10:1
    |
 LL | impl Into<StringWrapper> for String {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -13,7 +13,7 @@ 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
+  --> $DIR/from_over_into.rs:18:1
    |
 LL | impl Into<SelfType> for String {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -26,7 +26,7 @@ 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
+  --> $DIR/from_over_into.rs:33:1
    |
 LL | impl Into<SelfKeywords> for X {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -41,7 +41,7 @@ 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
+  --> $DIR/from_over_into.rs:45:1
    |
 LL | impl core::convert::Into<bool> for crate::ExplicitPaths {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -59,7 +59,7 @@ LL ~         val.0
    |
 
 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:77:5
+  --> $DIR/from_over_into.rs:78:5
    |
 LL |     impl<T> Into<FromOverInto<T>> for Vec<T> {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^