Add tests for extension of unconditional_recursion lint on Default trait

tests/ui/unconditional_recursion.rs

@@ -1,7 +1,7 @@
 //@no-rustfix
 
 #![warn(clippy::unconditional_recursion)]
-#![allow(clippy::partialeq_ne_impl)]
+#![allow(clippy::partialeq_ne_impl, clippy::default_constructed_unit_structs)]
 
 enum Foo {
     A,
@@ -232,6 +232,38 @@ fn to_string(&self) -> String {
     }
 }
 
+struct S12;
+
+impl std::default::Default for S12 {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl S12 {
+    fn new() -> Self {
+        //~^ ERROR: function cannot return without recursing
+        Self::default()
+    }
+
+    fn bar() -> Self {
+        // Should not warn!
+        Self::default()
+    }
+}
+
+#[derive(Default)]
+struct S13 {
+    f: u32,
+}
+
+impl S13 {
+    fn new() -> Self {
+        // Shoud not warn!
+        Self::default()
+    }
+}
+
 fn main() {
     // test code goes here
 }

tests/ui/unconditional_recursion.stderr

@@ -325,5 +325,20 @@ note: recursive call site
 LL |         mine == theirs
    |         ^^^^^^^^^^^^^^
 
-error: aborting due to 25 previous errors
+error: function cannot return without recursing
+  --> $DIR/unconditional_recursion.rs:244:5
+   |
+LL | /     fn new() -> Self {
+LL | |
+LL | |         Self::default()
+LL | |     }
+   | |_____^
+   |
+note: recursive call site
+  --> $DIR/unconditional_recursion.rs:246:9
+   |
+LL |         Self::default()
+   |         ^^^^^^^^^^^^^^^
+
+error: aborting due to 26 previous errors