Add autoderef and autoref tests for future_prelude_collision lint

Author: jam1garner

src/test/ui/lint/future-prelude-collision.fixed

@@ -12,6 +12,13 @@ impl TryIntoU32 for u8 {
     }
 }
 
+// needed for autoref test
+impl TryIntoU32 for &f32 {
+    fn try_into(self) -> Result<u32, ()> {
+        Ok(*self as u32)
+    }
+}
+
 trait TryFromU8: Sized {
     fn try_from(x: u8) -> Result<Self, ()>;
 }
@@ -54,4 +61,12 @@ fn main() {
     // test type omission
     let _: u32 = <_ as TryFromU8>::try_from(3u8).unwrap();
     //~^ WARNING trait-associated function `try_from` will become ambiguous in Rust 2021
+
+    // test autoderef
+    let _: u32 = TryIntoU32::try_into(*(&3u8)).unwrap();
+    //~^ WARNING trait method `try_into` will become ambiguous in Rust 2021
+
+    // test autoref
+    let _: u32 = TryIntoU32::try_into(&3.0).unwrap();
+    //~^ WARNING trait method `try_into` will become ambiguous in Rust 2021
 }

src/test/ui/lint/future-prelude-collision.rs

@@ -12,6 +12,13 @@ impl TryIntoU32 for u8 {
     }
 }
 
+// needed for autoref test
+impl TryIntoU32 for &f32 {
+    fn try_into(self) -> Result<u32, ()> {
+        Ok(*self as u32)
+    }
+}
+
 trait TryFromU8: Sized {
     fn try_from(x: u8) -> Result<Self, ()>;
 }
@@ -54,4 +61,12 @@ fn main() {
     // test type omission
     let _: u32 = <_>::try_from(3u8).unwrap();
     //~^ WARNING trait-associated function `try_from` will become ambiguous in Rust 2021
+
+    // test autoderef
+    let _: u32 = (&3u8).try_into().unwrap();
+    //~^ WARNING trait method `try_into` will become ambiguous in Rust 2021
+
+    // test autoref
+    let _: u32 = 3.0.try_into().unwrap();
+    //~^ WARNING trait method `try_into` will become ambiguous in Rust 2021
 }

src/test/ui/lint/future-prelude-collision.stderr

@@ -1,28 +1,40 @@
 warning: trait method `try_into` will become ambiguous in Rust 2021
-  --> $DIR/future-prelude-collision.rs:40:18
+  --> $DIR/future-prelude-collision.rs:47:18
    |
 LL |     let _: u32 = 3u8.try_into().unwrap();
    |                  ^^^^^^^^^^^^^^ help: disambiguate the associated function: `TryIntoU32::try_into(3u8)`
    |
    = note: `#[warn(future_prelude_collision)]` on by default
 
 warning: trait-associated function `try_from` will become ambiguous in Rust 2021
-  --> $DIR/future-prelude-collision.rs:44:13
+  --> $DIR/future-prelude-collision.rs:51:13
    |
 LL |     let _ = u32::try_from(3u8).unwrap();
    |             ^^^^^^^^^^^^^ help: disambiguate the associated function: `<u32 as TryFromU8>::try_from`
 
 warning: trait-associated function `from_iter` will become ambiguous in Rust 2021
-  --> $DIR/future-prelude-collision.rs:48:13
+  --> $DIR/future-prelude-collision.rs:55:13
    |
 LL |     let _ = <Vec<u8>>::from_iter(vec![1u8, 2, 3, 4, 5, 6].into_iter());
    |             ^^^^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `<Vec<u8> as FromByteIterator>::from_iter`
 
 warning: trait-associated function `try_from` will become ambiguous in Rust 2021
-  --> $DIR/future-prelude-collision.rs:55:18
+  --> $DIR/future-prelude-collision.rs:62:18
    |
 LL |     let _: u32 = <_>::try_from(3u8).unwrap();
    |                  ^^^^^^^^^^^^^ help: disambiguate the associated function: `<_ as TryFromU8>::try_from`
 
-warning: 4 warnings emitted
+warning: trait method `try_into` will become ambiguous in Rust 2021
+  --> $DIR/future-prelude-collision.rs:66:18
+   |
+LL |     let _: u32 = (&3u8).try_into().unwrap();
+   |                  ^^^^^^^^^^^^^^^^^ help: disambiguate the associated function: `TryIntoU32::try_into(*(&3u8))`
+
+warning: trait method `try_into` will become ambiguous in Rust 2021
+  --> $DIR/future-prelude-collision.rs:70:18
+   |
+LL |     let _: u32 = 3.0.try_into().unwrap();
+   |                  ^^^^^^^^^^^^^^ help: disambiguate the associated function: `TryIntoU32::try_into(&3.0)`
+
+warning: 6 warnings emitted