Rollup merge of #79181 - aDotInTheVoid:provided-method-source-link, r=jyn514,GuillaumeGomez

rustdoc: add [src] links to methods on a trait's page

Closes #45150

![image](https://user-images.githubusercontent.com/28781354/99565541-aba4d500-29c3-11eb-99c7-11c1f91584e9.png)

### Caveats

- The way I've implemented it, links are also provided for required methods, that just link to the signature in the code. I'm not sure if this is the desired behaviour.

![image](https://user-images.githubusercontent.com/28781354/99566222-849ad300-29c4-11eb-9897-08cc5842954f.png)

- I'm not sure if the css changes are correct. I inspected them visualy on firefox on desktop, and they seem to be fine.
- I can't tell how `src/librustdoc/html/render/mod.rs` is structured, so I probably

3 files changed, 55 insertions, 42 deletions

diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index 28f7a4d3162..147a8d33765 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -1194,6 +1194,16 @@ fn write_minify(
     }
 }
 
+fn write_srclink(cx: &Context, item: &clean::Item, buf: &mut Buffer, cache: &Cache) {
+    if let Some(l) = cx.src_href(item, cache) {
+        write!(
+            buf,
+            "<a class=\"srclink\" href=\"{}\" title=\"{}\">[src]</a>",
+            l, "goto source code"
+        )
+    }
+}
+
 #[derive(Debug, Eq, PartialEq, Hash)]
 struct ItemEntry {
     url: String,
@@ -1706,13 +1716,7 @@ fn print_item(cx: &Context, item: &clean::Item, buf: &mut Buffer, cache: &Cache)
     // this page, and this link will be auto-clicked. The `id` attribute is
     // used to find the link to auto-click.
     if cx.shared.include_sources && !item.is_primitive() {
-        if let Some(l) = cx.src_href(item, cache) {
-            write!(
-                buf,
-                "<a class=\"srclink\" href=\"{}\" title=\"{}\">[src]</a>",
-                l, "goto source code"
-            );
-        }
+        write_srclink(cx, item, buf, cache);
     }
 
     write!(buf, "</span>"); // out-of-band
@@ -2624,7 +2628,7 @@ fn item_trait(w: &mut Buffer, cx: &Context, it: &clean::Item, t: &clean::Trait,
         write!(w, "{}<span class=\"loading-content\">Loading content...</span>", extra_content)
     }
 
-    fn trait_item(w: &mut Buffer, cx: &Context, m: &clean::Item, t: &clean::Item) {
+    fn trait_item(w: &mut Buffer, cx: &Context, m: &clean::Item, t: &clean::Item, cache: &Cache) {
         let name = m.name.as_ref().unwrap();
         info!("Documenting {} on {}", name, t.name.as_deref().unwrap_or_default());
         let item_type = m.type_();
@@ -2633,6 +2637,7 @@ fn item_trait(w: &mut Buffer, cx: &Context, it: &clean::Item, t: &clean::Trait,
         render_assoc_item(w, m, AssocItemLink::Anchor(Some(&id)), ItemType::Impl);
         write!(w, "</code>");
         render_stability_since(w, m, t);
+        write_srclink(cx, m, w, cache);
         write!(w, "</h3>");
         document(w, cx, m, Some(t));
     }
@@ -2644,8 +2649,8 @@ fn item_trait(w: &mut Buffer, cx: &Context, it: &clean::Item, t: &clean::Trait,
             "Associated Types",
             "<div class=\"methods\">",
         );
-        for t in &types {
-            trait_item(w, cx, *t, it);
+        for t in types {
+            trait_item(w, cx, t, it, cache);
         }
         write_loading_content(w, "</div>");
     }
@@ -2657,8 +2662,8 @@ fn item_trait(w: &mut Buffer, cx: &Context, it: &clean::Item, t: &clean::Trait,
             "Associated Constants",
             "<div class=\"methods\">",
         );
-        for t in &consts {
-            trait_item(w, cx, *t, it);
+        for t in consts {
+            trait_item(w, cx, t, it, cache);
         }
         write_loading_content(w, "</div>");
     }
@@ -2671,8 +2676,8 @@ fn item_trait(w: &mut Buffer, cx: &Context, it: &clean::Item, t: &clean::Trait,
             "Required methods",
             "<div class=\"methods\">",
         );
-        for m in &required {
-            trait_item(w, cx, *m, it);
+        for m in required {
+            trait_item(w, cx, m, it, cache);
         }
         write_loading_content(w, "</div>");
     }
@@ -2683,8 +2688,8 @@ fn item_trait(w: &mut Buffer, cx: &Context, it: &clean::Item, t: &clean::Trait,
             "Provided methods",
             "<div class=\"methods\">",
         );
-        for m in &provided {
-            trait_item(w, cx, *m, it);
+        for m in provided {
+            trait_item(w, cx, m, it, cache);
         }
         write_loading_content(w, "</div>");
     }
@@ -3693,13 +3698,7 @@ fn render_impl(
             StabilityLevel::Unstable { .. } => None,
         });
         render_stability_since_raw(w, since.as_deref(), outer_version);
-        if let Some(l) = cx.src_href(&i.impl_item, cache) {
-            write!(
-                w,
-                "<a class=\"srclink\" href=\"{}\" title=\"{}\">[src]</a>",
-                l, "goto source code"
-            );
-        }
+        write_srclink(cx, &i.impl_item, w, cache);
         write!(w, "</h3>");
 
         if trait_.is_some() {
@@ -3765,13 +3764,7 @@ fn render_impl(
                     render_assoc_item(w, item, link.anchor(&id), ItemType::Impl);
                     write!(w, "</code>");
                     render_stability_since_raw(w, item.stable_since().as_deref(), outer_version);
-                    if let Some(l) = cx.src_href(item, cache) {
-                        write!(
-                            w,
-                            "<a class=\"srclink\" href=\"{}\" title=\"{}\">[src]</a>",
-                            l, "goto source code"
-                        );
-                    }
+                    write_srclink(cx, item, w, cache);
                     write!(w, "</h4>");
                 }
             }
@@ -3787,13 +3780,7 @@ fn render_impl(
                 assoc_const(w, item, ty, default.as_ref(), link.anchor(&id), "");
                 write!(w, "</code>");
                 render_stability_since_raw(w, item.stable_since().as_deref(), outer_version);
-                if let Some(l) = cx.src_href(item, cache) {
-                    write!(
-                        w,
-                        "<a class=\"srclink\" href=\"{}\" title=\"{}\">[src]</a>",
-                        l, "goto source code"
-                    );
-                }
+                write_srclink(cx, item, w, cache);
                 write!(w, "</h4>");
             }
             clean::AssocTypeItem(ref bounds, ref default) => {
diff --git a/src/librustdoc/html/static/rustdoc.css b/src/librustdoc/html/static/rustdoc.css
index 7eccb09b073..7d22913b99d 100644
--- a/src/librustdoc/html/static/rustdoc.css
+++ b/src/librustdoc/html/static/rustdoc.css
@@ -659,7 +659,7 @@ a {
 	text-decoration: underline;
 }
 
-.invisible > .srclink, h4 > code + .srclink {
+.invisible > .srclink, h4 > code + .srclink, h3 > code + .srclink {
 	position: absolute;
 	top: 0;
 	right: 0;
@@ -857,25 +857,25 @@ body.blur > :not(#help) {
 	top: 0;
 }
 
-.impl-items .since, .impl .since {
+.impl-items .since, .impl .since, .methods .since {
 	flex-grow: 0;
 	padding-left: 12px;
 	padding-right: 2px;
 	position: initial;
 }
 
-.impl-items .srclink, .impl .srclink {
+.impl-items .srclink, .impl .srclink, .methods .srclink {
 	flex-grow: 0;
 	/* Override header settings otherwise it's too bold */
 	font-size: 17px;
 	font-weight: normal;
 }
 
-.impl-items code, .impl code {
+.impl-items code, .impl code, .methods code {
 	flex-grow: 1;
 }
 
-.impl-items h4, h4.impl, h3.impl {
+.impl-items h4, h4.impl, h3.impl, .methods h3 {
 	display: flex;
 	flex-basis: 100%;
 	font-size: 16px;
diff --git a/src/test/rustdoc/trait-src-link.rs b/src/test/rustdoc/trait-src-link.rs
new file mode 100644
index 00000000000..77116695690
--- /dev/null
+++ b/src/test/rustdoc/trait-src-link.rs
@@ -0,0 +1,26 @@
+#![crate_name = "quix"]
+pub trait Foo {
+    // @has quix/trait.Foo.html '//a[@href="../src/quix/trait-src-link.rs.html#4"]' '[src]'
+    fn required();
+
+    // @has quix/trait.Foo.html '//a[@href="../src/quix/trait-src-link.rs.html#7"]' '[src]'
+    fn provided() {}
+}
+
+pub struct Bar;
+
+impl Foo for Bar {
+    // @has quix/struct.Bar.html '//a[@href="../src/quix/trait-src-link.rs.html#14"]' '[src]'
+    fn required() {}
+    // @has quix/struct.Bar.html '//a[@href="../src/quix/trait-src-link.rs.html#7"]' '[src]'
+}
+
+pub struct Baz;
+
+impl Foo for Baz {
+    // @has quix/struct.Baz.html '//a[@href="../src/quix/trait-src-link.rs.html#22"]' '[src]'
+    fn required() {}
+
+    // @has quix/struct.Baz.html '//a[@href="../src/quix/trait-src-link.rs.html#25"]' '[src]'
+    fn provided() {}
+}