rustdoc: Populate external_traits with traits only seen in impls

src/librustdoc/clean/inline.rs

@@ -349,6 +349,9 @@ pub fn build_impl(cx: &DocContext, did: DefId, ret: &mut Vec<clean::Item>) {
     if trait_.def_id() == tcx.lang_items().deref_trait() {
         super::build_deref_target_impls(cx, &trait_items, ret);
     }
+    if let Some(trait_did) = trait_.def_id() {
+        record_extern_trait(cx, trait_did);
+    }
 
     let provided = trait_.def_id().map(|did| {
         tcx.provided_trait_methods(did)
@@ -504,3 +507,9 @@ fn separate_supertrait_bounds(mut g: clean::Generics)
     });
     (g, ty_bounds)
 }
+
+pub fn record_extern_trait(cx: &DocContext, did: DefId) {
+    cx.external_traits.borrow_mut().entry(did).or_insert_with(|| {
+        build_external_trait(cx, did)
+    });
+}

src/librustdoc/clean/mod.rs

@@ -3189,8 +3189,7 @@ fn register_def(cx: &DocContext, def: Def) -> DefId {
     if did.is_local() { return did }
     inline::record_extern_fqn(cx, did, kind);
     if let TypeKind::Trait = kind {
-        let t = inline::build_external_trait(cx, did);
-        cx.external_traits.borrow_mut().insert(did, t);
+        inline::record_extern_trait(cx, did);
     }
     did
 }

src/librustdoc/html/render.rs

@@ -3291,8 +3291,7 @@ fn spotlight_decl(decl: &clean::FnDecl) -> Result<String, fmt::Error> {
         if let Some(impls) = c.impls.get(&did) {
             for i in impls {
                 let impl_ = i.inner_impl();
-                if impl_.trait_.def_id().and_then(|d| c.traits.get(&d))
-                                        .map_or(false, |t| t.is_spotlight) {
+                if impl_.trait_.def_id().map_or(false, |d| c.traits[&d].is_spotlight) {
                     if out.is_empty() {
                         out.push_str(
                             &format!("<h3 class=\"important\">Important traits for {}</h3>\
@@ -3458,7 +3457,7 @@ fn render_impl(w: &mut fmt::Formatter, cx: &Context, i: &Impl, link: AssocItemLi
     }
 
     let traits = &cache().traits;
-    let trait_ = i.trait_did().and_then(|did| traits.get(&did));
+    let trait_ = i.trait_did().map(|did| &traits[&did]);
 
     if !show_def_docs {
         write!(w, "<span class='docblock autohide'>")?;

src/test/rustdoc/inline_cross/auxiliary/impl-inline-without-trait.rs

@@ -0,0 +1,18 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub trait MyTrait {
+    /// docs for my_trait_method
+    fn my_trait_method() {}
+}
+
+pub struct MyStruct;
+
+impl MyTrait for MyStruct {}

src/test/rustdoc/inline_cross/impl-inline-without-trait.rs

@@ -0,0 +1,22 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// aux-build:impl-inline-without-trait.rs
+// build-aux-docs
+// ignore-cross-compile
+
+#![crate_name = "foo"]
+
+extern crate impl_inline_without_trait;
+
+// @has 'foo/struct.MyStruct.html'
+// @has - '//*[@id="method.my_trait_method"]' 'fn my_trait_method()'
+// @has - '//*[@class="docblock"]' 'docs for my_trait_method'
+pub use impl_inline_without_trait::MyStruct;