Auto merge of #105575 - compiler-errors:impl-wf-lint, r=oli-obk

Add `IMPLIED_BOUNDS_ENTAILMENT` lint

Implements a lint (#105572) version of the hard-error introduced in #105483. Context is in that PR.

r? `@lcnr`
cc `@oli-obk` who had asked for this to be a lint first

Not sure if this needs to be an FCP, since it's a lint for now.

4 files changed, 75 insertions, 0 deletions

diff --git a/src/test/ui/implied-bounds/impl-implied-bounds-compatibility-unnormalized.rs b/src/test/ui/implied-bounds/impl-implied-bounds-compatibility-unnormalized.rs
new file mode 100644
index 00000000000..6ccbb5bb266
--- /dev/null
+++ b/src/test/ui/implied-bounds/impl-implied-bounds-compatibility-unnormalized.rs
@@ -0,0 +1,22 @@
+#![deny(implied_bounds_entailment)]
+
+trait Project {
+    type Ty;
+}
+impl Project for &'_ &'_ () {
+    type Ty = ();
+}
+trait Trait {
+    fn get<'s>(s: &'s str, _: ()) -> &'static str;
+}
+impl Trait for () {
+    fn get<'s>(s: &'s str, _: <&'static &'s () as Project>::Ty) -> &'static str {
+        //~^ ERROR impl method assumes more implied bounds than the corresponding trait method
+        //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+        s
+    }
+}
+fn main() {
+    let val = <() as Trait>::get(&String::from("blah blah blah"), ());
+    println!("{}", val);
+}
diff --git a/src/test/ui/implied-bounds/impl-implied-bounds-compatibility-unnormalized.stderr b/src/test/ui/implied-bounds/impl-implied-bounds-compatibility-unnormalized.stderr
new file mode 100644
index 00000000000..0ac31c642eb
--- /dev/null
+++ b/src/test/ui/implied-bounds/impl-implied-bounds-compatibility-unnormalized.stderr
@@ -0,0 +1,16 @@
+error: impl method assumes more implied bounds than the corresponding trait method
+  --> $DIR/impl-implied-bounds-compatibility-unnormalized.rs:13:5
+   |
+LL |     fn get<'s>(s: &'s str, _: <&'static &'s () as Project>::Ty) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #105572 <https://github.com/rust-lang/rust/issues/105572>
+note: the lint level is defined here
+  --> $DIR/impl-implied-bounds-compatibility-unnormalized.rs:1:9
+   |
+LL | #![deny(implied_bounds_entailment)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/implied-bounds/impl-implied-bounds-compatibility.rs b/src/test/ui/implied-bounds/impl-implied-bounds-compatibility.rs
new file mode 100644
index 00000000000..d097bc16a22
--- /dev/null
+++ b/src/test/ui/implied-bounds/impl-implied-bounds-compatibility.rs
@@ -0,0 +1,21 @@
+#![deny(implied_bounds_entailment)]
+
+use std::cell::RefCell;
+
+pub struct MessageListeners<'a> {
+    listeners: RefCell<Vec<Box<dyn FnMut(()) + 'a>>>,
+}
+
+pub trait MessageListenersInterface {
+    fn listeners<'c>(&'c self) -> &'c MessageListeners<'c>;
+}
+
+impl<'a> MessageListenersInterface for MessageListeners<'a> {
+    fn listeners<'b>(&'b self) -> &'a MessageListeners<'b> {
+        //~^ ERROR impl method assumes more implied bounds than the corresponding trait method
+        //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+        self
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/implied-bounds/impl-implied-bounds-compatibility.stderr b/src/test/ui/implied-bounds/impl-implied-bounds-compatibility.stderr
new file mode 100644
index 00000000000..0dfa8167a99
--- /dev/null
+++ b/src/test/ui/implied-bounds/impl-implied-bounds-compatibility.stderr
@@ -0,0 +1,16 @@
+error: impl method assumes more implied bounds than the corresponding trait method
+  --> $DIR/impl-implied-bounds-compatibility.rs:14:5
+   |
+LL |     fn listeners<'b>(&'b self) -> &'a MessageListeners<'b> {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #105572 <https://github.com/rust-lang/rust/issues/105572>
+note: the lint level is defined here
+  --> $DIR/impl-implied-bounds-compatibility.rs:1:9
+   |
+LL | #![deny(implied_bounds_entailment)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+