Allow to not switch to a theme if it doesn't exist

Author: GuillaumeGomez

src/librustdoc/html/static/main.js

@@ -96,14 +96,6 @@
         }
     }
 
-    function onEach(arr, func) {
-        if (arr && arr.length > 0 && func) {
-            for (var i = 0; i < arr.length; i++) {
-                func(arr[i]);
-            }
-        }
-    }
-
     function isHidden(elem) {
         return (elem.offsetParent === null)
     }

src/librustdoc/html/static/storage.js

@@ -13,6 +13,18 @@
 var currentTheme = document.getElementById("themeStyle");
 var mainTheme = document.getElementById("mainThemeStyle");
 
+var savedHref = [];
+
+function onEach(arr, func) {
+    if (arr && arr.length > 0 && func) {
+        for (var i = 0; i < arr.length; i++) {
+            if (func(arr[i]) === true) {
+                break;
+            }
+        }
+    }
+}
+
 function updateLocalStorage(name, value) {
     if (typeof(Storage) !== "undefined") {
         localStorage[name] = value;
@@ -29,8 +41,24 @@ function getCurrentValue(name) {
 }
 
 function switchTheme(styleElem, mainStyleElem, newTheme) {
-    styleElem.href = mainStyleElem.href.replace("rustdoc.css", newTheme + ".css");
-    updateLocalStorage('rustdoc-theme', newTheme);
+    var newHref = mainStyleElem.href.replace("rustdoc.css", newTheme + ".css");
+    var found = false;
+
+    if (savedHref.length === 0) {
+        onEach(document.getElementsByTagName("link"), function(el) {
+            savedHref.push(el.href);
+        });
+    }
+    onEach(savedHref, function(el) {
+        if (el === newHref) {
+            found = true;
+            return true;
+        }
+    });
+    if (found === true) {
+        styleElem.href = newHref;
+        updateLocalStorage('rustdoc-theme', newTheme);
+    }
 }
 
-switchTheme(currentTheme, mainTheme, getCurrentValue('theme') || 'main');
+switchTheme(currentTheme, mainTheme, getCurrentValue('rustdoc-theme') || 'main');