Rollup merge of rust-lang#76783 - lzutao:rd_impl_kind, r=GuillaumeGomez

Only get ImplKind::Impl once

With this, the code panics in one place instead of two.

Author: RalfJung

src/librustdoc/clean/inline.rs

@@ -352,14 +352,22 @@ pub fn build_impl(
         }
     }
 
-    let for_ = if let Some(did) = did.as_local() {
-        let hir_id = tcx.hir().local_def_id_to_hir_id(did);
-        match tcx.hir().expect_item(hir_id).kind {
-            hir::ItemKind::Impl { self_ty, .. } => self_ty.clean(cx),
-            _ => panic!("did given to build_impl was not an impl"),
+    let impl_item = match did.as_local() {
+        Some(did) => {
+            let hir_id = tcx.hir().local_def_id_to_hir_id(did);
+            match tcx.hir().expect_item(hir_id).kind {
+                hir::ItemKind::Impl { self_ty, ref generics, ref items, .. } => {
+                    Some((self_ty, generics, items))
+                }
+                _ => panic!("`DefID` passed to `build_impl` is not an `impl"),
+            }
         }
-    } else {
-        tcx.type_of(did).clean(cx)
+        None => None,
+    };
+
+    let for_ = match impl_item {
+        Some((self_ty, _, _)) => self_ty.clean(cx),
+        None => tcx.type_of(did).clean(cx),
     };
 
     // Only inline impl if the implementing type is
@@ -379,17 +387,12 @@ pub fn build_impl(
     }
 
     let predicates = tcx.explicit_predicates_of(did);
-    let (trait_items, generics) = if let Some(did) = did.as_local() {
-        let hir_id = tcx.hir().local_def_id_to_hir_id(did);
-        match tcx.hir().expect_item(hir_id).kind {
-            hir::ItemKind::Impl { ref generics, ref items, .. } => (
-                items.iter().map(|item| tcx.hir().impl_item(item.id).clean(cx)).collect::<Vec<_>>(),
-                generics.clean(cx),
-            ),
-            _ => panic!("did given to build_impl was not an impl"),
-        }
-    } else {
-        (
+    let (trait_items, generics) = match impl_item {
+        Some((_, generics, items)) => (
+            items.iter().map(|item| tcx.hir().impl_item(item.id).clean(cx)).collect::<Vec<_>>(),
+            generics.clean(cx),
+        ),
+        None => (
             tcx.associated_items(did)
                 .in_definition_order()
                 .filter_map(|item| {
@@ -401,7 +404,7 @@ pub fn build_impl(
                 })
                 .collect::<Vec<_>>(),
             clean::enter_impl_trait(cx, || (tcx.generics_of(did), predicates).clean(cx)),
-        )
+        ),
     };
     let polarity = tcx.impl_polarity(did);
     let trait_ = associated_trait.clean(cx).map(|bound| match bound {