Add and update tests.

src/test/ui/rust-2021/future-prelude-collision-generic-trait.fixed

+// See https://github.com/rust-lang/rust/issues/88470
+// run-rustfix
+// edition:2018
+// check-pass
+#![warn(rust_2021_prelude_collisions)]
+#![allow(dead_code)]
+#![allow(unused_imports)]
+
+pub trait PyTryFrom<'v, T>: Sized {
+    fn try_from<V>(value: V) -> Result<&'v Self, T>;
+}
+
+pub trait PyTryInto<T>: Sized {
+    fn try_into(&self) -> Result<&T, i32>;
+}
+
+struct Foo;
+
+impl<U> PyTryInto<U> for Foo
+where
+    U: for<'v> PyTryFrom<'v, i32>,
+{
+    fn try_into(&self) -> Result<&U, i32> {
+        <U as PyTryFrom<'_, _>>::try_from(self)
+        //~^ WARNING trait-associated function `try_from` will become ambiguous in Rust 2021
+        //~| this is accepted in the current edition (Rust 2018)
+    }
+}
+
+fn main() {}

src/test/ui/rust-2021/future-prelude-collision-generic-trait.rs

+// See https://github.com/rust-lang/rust/issues/88470
+// run-rustfix
+// edition:2018
+// check-pass
+#![warn(rust_2021_prelude_collisions)]
+#![allow(dead_code)]
+#![allow(unused_imports)]
+
+pub trait PyTryFrom<'v, T>: Sized {
+    fn try_from<V>(value: V) -> Result<&'v Self, T>;
+}
+
+pub trait PyTryInto<T>: Sized {
+    fn try_into(&self) -> Result<&T, i32>;
+}
+
+struct Foo;
+
+impl<U> PyTryInto<U> for Foo
+where
+    U: for<'v> PyTryFrom<'v, i32>,
+{
+    fn try_into(&self) -> Result<&U, i32> {
+        U::try_from(self)
+        //~^ WARNING trait-associated function `try_from` will become ambiguous in Rust 2021
+        //~| this is accepted in the current edition (Rust 2018)
+    }
+}
+
+fn main() {}

src/test/ui/rust-2021/future-prelude-collision-generic-trait.stderr

+warning: trait-associated function `try_from` will become ambiguous in Rust 2021
+  --> $DIR/future-prelude-collision-generic-trait.rs:24:9
+   |
+LL |         U::try_from(self)
+   |         ^^^^^^^^^^^ help: disambiguate the associated function: `<U as PyTryFrom<'_, _>>::try_from`
+   |
+note: the lint level is defined here
+  --> $DIR/future-prelude-collision-generic-trait.rs:5:9
+   |
+LL | #![warn(rust_2021_prelude_collisions)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/prelude.html>
+
+warning: 1 warning emitted
+

src/test/ui/rust-2021/future-prelude-collision-generic.fixed

@@ -6,32 +6,32 @@
 #![allow(dead_code)]
 #![allow(unused_imports)]
 
-struct Generic<T, U>(T, U);
+struct Generic<'a, U>(&'a U);
 
 trait MyFromIter {
     fn from_iter(_: i32) -> Self;
 }
 
-impl MyFromIter for Generic<i32, i32> {
-    fn from_iter(x: i32) -> Self {
-        Self(x, x)
+impl MyFromIter for Generic<'static, i32> {
+    fn from_iter(_: i32) -> Self {
+        todo!()
     }
 }
 
-impl std::iter::FromIterator<i32> for Generic<i32, i32> {
+impl std::iter::FromIterator<i32> for Generic<'static, i32> {
     fn from_iter<T: IntoIterator<Item = i32>>(_: T) -> Self {
         todo!()
     }
 }
 
 fn main() {
-    <Generic<_, _> as MyFromIter>::from_iter(1);
+    <Generic<'_, _> as MyFromIter>::from_iter(1);
     //~^ WARNING trait-associated function `from_iter` will become ambiguous in Rust 2021
     //~| this is accepted in the current edition (Rust 2018)
-    <Generic::<i32, i32> as MyFromIter>::from_iter(1);
+    <Generic::<'static, i32> as MyFromIter>::from_iter(1);
     //~^ WARNING trait-associated function `from_iter` will become ambiguous in Rust 2021
     //~| this is accepted in the current edition (Rust 2018)
-    <Generic::<_, _> as MyFromIter>::from_iter(1);
+    <Generic::<'_, _> as MyFromIter>::from_iter(1);
     //~^ WARNING trait-associated function `from_iter` will become ambiguous in Rust 2021
     //~| this is accepted in the current edition (Rust 2018)
 }

src/test/ui/rust-2021/future-prelude-collision-generic.rs

@@ -6,19 +6,19 @@
 #![allow(dead_code)]
 #![allow(unused_imports)]
 
-struct Generic<T, U>(T, U);
+struct Generic<'a, U>(&'a U);
 
 trait MyFromIter {
     fn from_iter(_: i32) -> Self;
 }
 
-impl MyFromIter for Generic<i32, i32> {
-    fn from_iter(x: i32) -> Self {
-        Self(x, x)
+impl MyFromIter for Generic<'static, i32> {
+    fn from_iter(_: i32) -> Self {
+        todo!()
     }
 }
 
-impl std::iter::FromIterator<i32> for Generic<i32, i32> {
+impl std::iter::FromIterator<i32> for Generic<'static, i32> {
     fn from_iter<T: IntoIterator<Item = i32>>(_: T) -> Self {
         todo!()
     }
@@ -28,10 +28,10 @@ fn main() {
     Generic::from_iter(1);
     //~^ WARNING trait-associated function `from_iter` will become ambiguous in Rust 2021
     //~| this is accepted in the current edition (Rust 2018)
-    Generic::<i32, i32>::from_iter(1);
+    Generic::<'static, i32>::from_iter(1);
     //~^ WARNING trait-associated function `from_iter` will become ambiguous in Rust 2021
     //~| this is accepted in the current edition (Rust 2018)
-    Generic::<_, _>::from_iter(1);
+    Generic::<'_, _>::from_iter(1);
     //~^ WARNING trait-associated function `from_iter` will become ambiguous in Rust 2021
     //~| this is accepted in the current edition (Rust 2018)
 }

src/test/ui/rust-2021/future-prelude-collision-generic.stderr

@@ -2,7 +2,7 @@ warning: trait-associated function `from_iter` will become ambiguous in Rust 202
   --> $DIR/future-prelude-collision-generic.rs:28:5
    |
 LL |     Generic::from_iter(1);
-   |     ^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `<Generic<_, _> as MyFromIter>::from_iter`
+   |     ^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `<Generic<'_, _> as MyFromIter>::from_iter`
    |
 note: the lint level is defined here
   --> $DIR/future-prelude-collision-generic.rs:5:9
@@ -15,8 +15,8 @@ LL | #![warn(rust_2021_prelude_collisions)]
 warning: trait-associated function `from_iter` will become ambiguous in Rust 2021
   --> $DIR/future-prelude-collision-generic.rs:31:5
    |
-LL |     Generic::<i32, i32>::from_iter(1);
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `<Generic::<i32, i32> as MyFromIter>::from_iter`
+LL |     Generic::<'static, i32>::from_iter(1);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `<Generic::<'static, i32> as MyFromIter>::from_iter`
    |
    = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/prelude.html>
@@ -24,8 +24,8 @@ LL |     Generic::<i32, i32>::from_iter(1);
 warning: trait-associated function `from_iter` will become ambiguous in Rust 2021
   --> $DIR/future-prelude-collision-generic.rs:34:5
    |
-LL |     Generic::<_, _>::from_iter(1);
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `<Generic::<_, _> as MyFromIter>::from_iter`
+LL |     Generic::<'_, _>::from_iter(1);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `<Generic::<'_, _> as MyFromIter>::from_iter`
    |
    = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/prelude.html>