chore: add test cases to verify ref and tmp checks

Author: aaron-ang

tests/ui/return_and_then.fixed

@@ -28,6 +28,19 @@ fn main() {
         test_res_block(Ok(n))
     }
 
+    fn test_ref_only() -> Option<i32> {
+        let x = Some("")?;
+        if x.len() > 2 { Some(3) } else { None }
+    }
+
+    fn test_tmp_only() -> Option<i32> {
+        let x = Some(match (vec![1, 2, 3], vec![1, 2, 4]) {
+            (a, _) if a.len() > 1 => a,
+            (_, b) => b,
+        })?;
+        if x.len() > 2 { Some(3) } else { None }
+    }
+
     // should not lint
     fn test_tmp_ref() -> Option<String> {
         String::from("<BOOM>")

tests/ui/return_and_then.rs

@@ -25,6 +25,18 @@ fn main() {
         opt.and_then(|n| test_res_block(Ok(n)))
     }
 
+    fn test_ref_only() -> Option<i32> {
+        Some("").and_then(|x| if x.len() > 2 { Some(3) } else { None })
+    }
+
+    fn test_tmp_only() -> Option<i32> {
+        Some(match (vec![1, 2, 3], vec![1, 2, 4]) {
+            (a, _) if a.len() > 1 => a,
+            (_, b) => b,
+        })
+        .and_then(|x| if x.len() > 2 { Some(3) } else { None })
+    }
+
     // should not lint
     fn test_tmp_ref() -> Option<String> {
         String::from("<BOOM>")

tests/ui/return_and_then.stderr

@@ -66,5 +66,36 @@ LL ~         let n = opt?;
 LL +         test_res_block(Ok(n))
    |
 
-error: aborting due to 5 previous errors
+error: use the question mark operator instead of an `and_then` call
+  --> tests/ui/return_and_then.rs:29:9
+   |
+LL |         Some("").and_then(|x| if x.len() > 2 { Some(3) } else { None })
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL ~         let x = Some("")?;
+LL +         if x.len() > 2 { Some(3) } else { None }
+   |
+
+error: use the question mark operator instead of an `and_then` call
+  --> tests/ui/return_and_then.rs:33:9
+   |
+LL | /         Some(match (vec![1, 2, 3], vec![1, 2, 4]) {
+LL | |             (a, _) if a.len() > 1 => a,
+LL | |             (_, b) => b,
+LL | |         })
+LL | |         .and_then(|x| if x.len() > 2 { Some(3) } else { None })
+   | |_______________________________________________________________^
+   |
+help: try
+   |
+LL ~         let x = Some(match (vec![1, 2, 3], vec![1, 2, 4]) {
+LL +             (a, _) if a.len() > 1 => a,
+LL +             (_, b) => b,
+LL +         })?;
+LL +         if x.len() > 2 { Some(3) } else { None }
+   |
+
+error: aborting due to 7 previous errors