From 507f10baee9ea0b884785aa4f54e3ffa6a1d82b2 Mon Sep 17 00:00:00 2001
From: y21 <30553356+y21@users.noreply.github.com>
Date: Tue, 29 Aug 2023 17:10:27 +0200
Subject: [PATCH] suggest removing `impl` in generic trait bound position

---
 compiler/rustc_parse/src/parser/ty.rs         | 36 +++++++++++++------
 .../suggest-removing-impl.rs                  | 14 ++++++++
 .../suggest-removing-impl.stderr              | 26 ++++++++++++++
 3 files changed, 65 insertions(+), 11 deletions(-)
 create mode 100644 tests/ui/associated-type-bounds/suggest-removing-impl.rs
 create mode 100644 tests/ui/associated-type-bounds/suggest-removing-impl.stderr

diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index 661113666cd..a25b0f1f893 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -891,18 +891,32 @@ impl<'a> Parser<'a> {
             // that we do not use the try operator when parsing the type because
             // if it fails then we get a parser error which we don't want (we're trying
             // to recover from errors, not make more).
-            let path = if self.may_recover()
-                && matches!(ty.kind, TyKind::Ptr(..) | TyKind::Ref(..))
-                && let TyKind::Path(_, path) = &ty.peel_refs().kind {
-                // Just get the indirection part of the type.
-                let span = ty.span.until(path.span);
+            let path = if self.may_recover() {
+                let (span, message, sugg, path, applicability) = match &ty.kind {
+                    TyKind::Ptr(..) | TyKind::Ref(..) if let TyKind::Path(_, path) = &ty.peel_refs().kind => {
+                        (
+                            ty.span.until(path.span),
+                            "consider removing the indirection",
+                            "",
+                            path,
+                            Applicability::MaybeIncorrect
+                        )
+                    }
+                    TyKind::ImplTrait(_, bounds)
+                        if let [GenericBound::Trait(tr, ..), ..] = bounds.as_slice() =>
+                    {
+                        (
+                            ty.span.until(tr.span),
+                            "use the trait bounds directly",
+                            "",
+                            &tr.trait_ref.path,
+                            Applicability::MachineApplicable
+                        )
+                    }
+                    _ => return Err(err)
+                };
 
-                err.span_suggestion_verbose(
-                    span,
-                    "consider removing the indirection",
-                    "",
-                    Applicability::MaybeIncorrect,
-                );
+                err.span_suggestion_verbose(span, message, sugg, applicability);
 
                 path.clone()
             } else {
diff --git a/tests/ui/associated-type-bounds/suggest-removing-impl.rs b/tests/ui/associated-type-bounds/suggest-removing-impl.rs
new file mode 100644
index 00000000000..242cd85727d
--- /dev/null
+++ b/tests/ui/associated-type-bounds/suggest-removing-impl.rs
@@ -0,0 +1,14 @@
+trait Tr {
+    type Assoc: impl Sized;
+    //~^ ERROR expected a trait, found type
+    //~| HELP use the trait bounds directly
+
+    fn fn_with_generics<T>()
+    where
+        T: impl Sized
+        //~^ ERROR expected a trait, found type
+        //~| HELP use the trait bounds directly
+    {}
+}
+
+fn main() {}
diff --git a/tests/ui/associated-type-bounds/suggest-removing-impl.stderr b/tests/ui/associated-type-bounds/suggest-removing-impl.stderr
new file mode 100644
index 00000000000..875b2db6deb
--- /dev/null
+++ b/tests/ui/associated-type-bounds/suggest-removing-impl.stderr
@@ -0,0 +1,26 @@
+error: expected a trait, found type
+  --> $DIR/suggest-removing-impl.rs:2:17
+   |
+LL |     type Assoc: impl Sized;
+   |                 ^^^^^^^^^^
+   |
+help: use the trait bounds directly
+   |
+LL -     type Assoc: impl Sized;
+LL +     type Assoc: Sized;
+   |
+
+error: expected a trait, found type
+  --> $DIR/suggest-removing-impl.rs:8:12
+   |
+LL |         T: impl Sized
+   |            ^^^^^^^^^^
+   |
+help: use the trait bounds directly
+   |
+LL -         T: impl Sized
+LL +         T: Sized
+   |
+
+error: aborting due to 2 previous errors
+