Fix auto-hide for implementations and implementors.

This sets their toggles to be closed in the HTML (matching the default
setting), and opens them if the setting indicates to do so.

This distinguishes between implementations and implementors based on
being descendants of certain named elements.

src/librustdoc/html/render/mod.rs

@@ -1545,7 +1545,7 @@ fn render_impl(
     let open_details = |close_tags: &mut String| {
         if toggled {
             close_tags.insert_str(0, "</details>");
-            "<details class=\"rustdoc-toggle implementors-toggle\" open><summary>"
+            "<details class=\"rustdoc-toggle implementors-toggle\"><summary>"
         } else {
             ""
         }

src/librustdoc/html/static/main.js

@@ -776,12 +776,29 @@ function hideThemeButtonState() {
 
         var hideMethodDocs = getSettingValue("auto-hide-method-docs") === "true";
         var hideImplementors = getSettingValue("auto-collapse-implementors") !== "false";
+        var hideImplementations = getSettingValue("auto-hide-trait-implementations") !== "false";
         var hideLargeItemContents = getSettingValue("auto-hide-large-items") !== "false";
 
-        onEachLazy(document.getElementsByTagName("details"), function (e) {
-            var showLargeItem = !hideLargeItemContents && hasClass(e, "type-contents-toggle");
-            var showImplementor = !hideImplementors && hasClass(e, "implementors-toggle");
-            if (showLargeItem || showImplementor) {
+        function openImplementors(id) {
+            var list = document.getElementById(id);
+            if (list !== null) {
+                onEachLazy(list.getElementsByClassName("implementors-toggle"), function(e) {
+                    e.open = true;
+                });
+            }
+        }
+
+        if (!hideImplementations) {
+            openImplementors("trait-implementations-list");
+            openImplementors("blanket-implementations-list");
+        }
+
+        if (!hideImplementors) {
+            openImplementors("implementors-list");
+        }
+
+        onEachLazy(document.getElementsByClassName("rustdoc-toggle"), function (e) {
+            if (!hideLargeItemContents && hasClass(e, "type-contents-toggle")) {
                 e.open = true;
             }
             if (hideMethodDocs && hasClass(e, "method-toggle")) {

src/test/rustdoc/manual_impl.rs

@@ -65,7 +65,8 @@ impl T for S2 {
 }
 
 // @has manual_impl/struct.S3.html '//*[@class="trait"]' 'T'
-// @has  - '//details[@open=""]/div[@class="docblock"]' 'Docs associated with the S3 trait implementation.'
+// @has  - '//details/div[@class="docblock"]' 'Docs associated with the S3 trait implementation.'
+// @!has  - '//details[@open=""]/div[@class="docblock"]' 'Docs associated with the S3 trait implementation.'
 // @has  - '//details[@open=""]/div[@class="docblock"]' 'Docs associated with the S3 trait b_method implementation.'
 // @!has - '//div[@class="impl-items"]/details[@open=""]//div[@class="docblock"]' 'Docs associated with the trait a_method definition.'
 // @has - '//div[@class="impl-items"]/details//div[@class="docblock"]' 'Docs associated with the trait a_method definition.'