Re-implement rust-lang#83826 unintrusively via a new command line flag.

Author: slightlyoutofphase

src/librustdoc/config.rs

@@ -276,6 +276,8 @@ crate struct RenderOptions {
     crate call_locations: AllCallLocations,
     /// If `true`, Context::init will not emit shared files.
     crate no_emit_shared: bool,
+    /// If `true`, "Methods From Deref" will be displayed after all other sections.
+    crate show_deref_methods_last: bool,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -658,6 +660,7 @@ impl Options {
         let generate_link_to_definition = matches.opt_present("generate-link-to-definition");
         let extern_html_root_takes_precedence =
             matches.opt_present("extern-html-root-takes-precedence");
+        let show_deref_methods_last = matches.opt_present("show-deref-methods-last");
 
         if generate_link_to_definition && (show_coverage || output_format != OutputFormat::Html) {
             diag.struct_err(
@@ -736,6 +739,7 @@ impl Options {
                 generate_link_to_definition,
                 call_locations,
                 no_emit_shared: false,
+                show_deref_methods_last,
             },
             crate_name,
             output_format,

src/librustdoc/html/render/context.rs

@@ -127,6 +127,8 @@ crate struct SharedContext<'tcx> {
     crate cache: Cache,
 
     crate call_locations: AllCallLocations,
+    /// If `true`, "Methods From Deref" will be displayed after all other sections.
+    crate show_deref_methods_last: bool,
 }
 
 impl SharedContext<'_> {
@@ -398,6 +400,7 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
             generate_link_to_definition,
             call_locations,
             no_emit_shared,
+            show_deref_methods_last,
             ..
         } = options;
 
@@ -485,6 +488,7 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
             span_correspondance_map: matches,
             cache,
             call_locations,
+            show_deref_methods_last,
         };
 
         // Add the default themes to the `Vec` of stylepaths

src/librustdoc/html/render/mod.rs

@@ -1105,12 +1105,18 @@ fn render_assoc_items_inner(
     }
 
     if !traits.is_empty() {
-        let deref_impl =
-            traits.iter().find(|t| t.trait_did() == cx.tcx().lang_items().deref_trait());
-        if let Some(impl_) = deref_impl {
-            let has_deref_mut =
-                traits.iter().any(|t| t.trait_did() == cx.tcx().lang_items().deref_mut_trait());
-            render_deref_methods(w, cx, impl_, containing_item, has_deref_mut, derefs);
+        let mut deref_methods = |w: &mut Buffer| {
+            let deref_impl =
+                traits.iter().find(|t| t.trait_did() == cx.tcx().lang_items().deref_trait());
+            if let Some(impl_) = deref_impl {
+                let has_deref_mut =
+                    traits.iter().any(|t| t.trait_did() == cx.tcx().lang_items().deref_mut_trait());
+                render_deref_methods(w, cx, impl_, containing_item, has_deref_mut, derefs);
+            }
+        };
+
+        if !cx.shared.show_deref_methods_last {
+            deref_methods(w);
         }
 
         // If we were already one level into rendering deref methods, we don't want to render
@@ -1161,6 +1167,10 @@ fn render_assoc_items_inner(
             render_impls(cx, w, &blanket_impl, containing_item);
             w.write_str("</div>");
         }
+
+        if cx.shared.show_deref_methods_last {
+            deref_methods(w);
+        }
     }
 }
 
@@ -2003,12 +2013,18 @@ fn sidebar_assoc_items(cx: &Context<'_>, out: &mut Buffer, it: &clean::Item) {
         }
 
         if v.iter().any(|i| i.inner_impl().trait_.is_some()) {
-            if let Some(impl_) =
-                v.iter().find(|i| i.trait_did() == cx.tcx().lang_items().deref_trait())
-            {
-                let mut derefs = FxHashSet::default();
-                derefs.insert(did);
-                sidebar_deref_methods(cx, out, impl_, v, &mut derefs);
+            let deref_methods = |out: &mut Buffer| {
+                if let Some(impl_) =
+                    v.iter().find(|i| i.trait_did() == cx.tcx().lang_items().deref_trait())
+                {
+                    let mut derefs = FxHashSet::default();
+                    derefs.insert(did);
+                    sidebar_deref_methods(cx, out, impl_, v, &mut derefs);
+                }
+            };
+
+            if !cx.shared.show_deref_methods_last {
+                deref_methods(out);
             }
 
             let format_impls = |impls: Vec<&Impl>| {
@@ -2077,6 +2093,10 @@ fn sidebar_assoc_items(cx: &Context<'_>, out: &mut Buffer, it: &clean::Item) {
                 );
                 write_sidebar_links(out, blanket_format);
             }
+
+            if cx.shared.show_deref_methods_last {
+                deref_methods(out);
+            }
         }
     }
 }

src/librustdoc/lib.rs

@@ -626,6 +626,13 @@ fn opts() -> Vec<RustcOptGroup> {
                 "path to function call information (for displaying examples in the documentation)",
             )
         }),
+        unstable("show-deref-methods-last", |o| {
+            o.optflagmulti(
+                "",
+                "show-deref-methods-last",
+                "display trait implementations before methods from deref",
+            )
+        }),
         // deprecated / removed options
         stable("plugin-path", |o| {
             o.optmulti(