Add a regression test for issue-72616

Author: JohnTitor

src/test/ui/inference/issue-72616.rs

@@ -0,0 +1,29 @@
+// Regression test for #72616, it used to emit incorrect diagnostics, like:
+// error[E0283]: type annotations needed for `String`
+//  --> src/main.rs:8:30
+//   |
+// 5 |         let _: String = "".to_owned().try_into().unwrap();
+//   |             - consider giving this pattern a type
+// ...
+// 8 |         if String::from("a") == "a".try_into().unwrap() {}
+//   |                              ^^ cannot infer type for struct `String`
+//   |
+//   = note: cannot satisfy `String: PartialEq<_>`
+
+use std::convert::TryInto;
+
+pub fn main() {
+    {
+        let _: String = "".to_owned().try_into().unwrap();
+    }
+    {
+        if String::from("a") == "a".try_into().unwrap() {}
+        //~^ ERROR: type annotations needed
+    }
+    {
+        let _: String = match "_".try_into() {
+            Ok(a) => a,
+            Err(_) => "".into(),
+        };
+    }
+}

src/test/ui/inference/issue-72616.stderr

@@ -0,0 +1,13 @@
+error[E0283]: type annotations needed
+  --> $DIR/issue-72616.rs:20:30
+   |
+LL |         if String::from("a") == "a".try_into().unwrap() {}
+   |                              ^^ -------------- this method call resolves to `std::result::Result<T, <Self as TryInto<T>>::Error>`
+   |                              |
+   |                              cannot infer type
+   |
+   = note: cannot satisfy `String: PartialEq<_>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0283`.