Sort impl associated items by kinds and then by appearance

Author: GuillaumeGomez

src/librustdoc/html/render/mod.rs

@@ -1794,13 +1794,64 @@ fn render_impl(
     let mut default_impl_items = Buffer::empty_from(w);
     let impl_ = i.inner_impl();
 
+    // Impl items are grouped by kinds:
+    //
+    // 1. Types
+    // 2. Constants
+    // 3. Functions
+    //
+    // This order is because you can have associated types in associated constants, and both in
+    // associcated functions. So with this order, when reading from top to bottom, you should always
+    // see all items definitions before they're actually used.
+    let mut assoc_consts = Vec::new();
+    let mut methods = Vec::new();
+
     if !impl_.is_negative_trait_impl() {
         for trait_item in &impl_.items {
+            match *trait_item.kind {
+                clean::MethodItem(..) | clean::TyMethodItem(_) => methods.push(trait_item),
+                clean::TyAssocConstItem(..) | clean::AssocConstItem(_) => {
+                    assoc_consts.push(trait_item)
+                }
+                clean::TyAssocTypeItem(..) | clean::AssocTypeItem(..) => {
+                    // We render it directly since they're supposed to come first.
+                    doc_impl_item(
+                        &mut default_impl_items,
+                        &mut impl_items,
+                        cx,
+                        trait_item,
+                        if trait_.is_some() { &i.impl_item } else { parent },
+                        link,
+                        render_mode,
+                        false,
+                        trait_,
+                        rendering_params,
+                    );
+                }
+                _ => {}
+            }
+        }
+
+        for assoc_const in assoc_consts {
             doc_impl_item(
                 &mut default_impl_items,
                 &mut impl_items,
                 cx,
-                trait_item,
+                assoc_const,
+                if trait_.is_some() { &i.impl_item } else { parent },
+                link,
+                render_mode,
+                false,
+                trait_,
+                rendering_params,
+            );
+        }
+        for method in methods {
+            doc_impl_item(
+                &mut default_impl_items,
+                &mut impl_items,
+                cx,
+                method,
                 if trait_.is_some() { &i.impl_item } else { parent },
                 link,
                 render_mode,