fix panicking bug

Author: mj10021

compiler/rustc_mir_build/src/lints.rs

@@ -36,10 +36,14 @@ use rustc_span::sym;
 fn is_default_impl<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> bool {
     if tcx.def_kind(def_id) == DefKind::AssocFn {
         // Check if this is a trait impl and get the defid of the trait if it is
-        if let Some(trait_def_id) = tcx.trait_id_of_impl(tcx.parent(def_id.into())) {
-            // check if it is a default impl
-            if tcx.get_diagnostic_name(trait_def_id) == Some(sym::Default) {
-                return true;
+        if let Some(parent_def_id) = tcx.opt_parent(def_id.into()) {
+            if tcx.def_kind(parent_def_id) == (DefKind::Impl {of_trait: true}) {
+                if let Some(trait_def_id) = tcx.trait_id_of_impl(parent_def_id) {
+                    // check if it is a default impl
+                    if tcx.get_diagnostic_name(trait_def_id) == Some(sym::Default) {
+                        return true;
+                    }
+                }
             }
         }
     }

tests/ui/lint/lint-unconditional-recursion.rs

@@ -177,18 +177,18 @@ pub fn overflow_check(a: i32, b: i32) { //~ ERROR function cannot return without
     overflow_check(a, b);
 }
 
-// pub struct Point {
-//     pub x: f32,
-//     pub y: f32,
-// }
-// 
-// impl Default for Point {
-//     fn default() -> Self { //~ ERROR function cannot return without recursing
-//         Point {
-//             x: Default::default(),
-//             ..Default::default()
-//         }
-//     }
-// }
+pub struct Point {
+    pub x: f32,
+    pub y: f32,
+}
+
+impl Default for Point {
+    fn default() -> Self { //~ ERROR function cannot return without recursing
+        Point {
+            x: Default::default(),
+            ..Default::default()
+        }
+    }
+}
 
 fn main() {}

tests/ui/lint/lint-unconditional-recursion.stderr

@@ -122,6 +122,7 @@ LL |         let x = Default::default();
    |                 ------------------ recursive call site
    |
    = help: a `loop` may express intention better if this is on purpose
+   = help: ..default() in the Default impl does not apply a default for each struct field
 
 error: function cannot return without recursing
   --> $DIR/lint-unconditional-recursion.rs:102:5
@@ -196,6 +197,7 @@ LL |             ..Default::default()
    |               ------------------ recursive call site
    |
    = help: a `loop` may express intention better if this is on purpose
+   = help: ..default() in the Default impl does not apply a default for each struct field
 
 error: aborting due to 18 previous errors