rustdoc: merge theme css into rustdoc.css

Based on
https://github.com/rust-lang/rust/pull/115812#issuecomment-1717960119

Having them in separate files used to make more sense, before the
migration to CSS variables made the theme files as small as they are
nowadays. This is already how docs.rs and mdBook do it.

1 files changed, 15 insertions, 11 deletions

diff --git a/src/librustdoc/html/static/js/storage.js b/src/librustdoc/html/static/js/storage.js
index af3ca42a6c0..ec34f5e8bf9 100644
--- a/src/librustdoc/html/static/js/storage.js
+++ b/src/librustdoc/html/static/js/storage.js
@@ -5,6 +5,7 @@
 // the page, so we don't see major layout changes during the load of the page.
 "use strict";
 
+const builtinThemes = ["light", "dark", "ayu"];
 const darkThemes = ["dark", "ayu"];
 window.currentTheme = document.getElementById("themeStyle");
 
@@ -119,19 +120,22 @@ function switchTheme(newThemeName, saveTheme) {
         updateLocalStorage("theme", newThemeName);
     }
 
-    let newHref;
+    document.documentElement.setAttribute("data-theme", newThemeName);
 
-    if (newThemeName === "light" || newThemeName === "dark" || newThemeName === "ayu") {
-        newHref = getVar("static-root-path") + getVar("theme-" + newThemeName + "-css");
+    if (builtinThemes.indexOf(newThemeName) !== -1) {
+        if (window.currentTheme) {
+            window.currentTheme.parentNode.removeChild(window.currentTheme);
+            window.currentTheme = null;
+        }
     } else {
-        newHref = getVar("root-path") + newThemeName + getVar("resource-suffix") + ".css";
-    }
-
-    if (!window.currentTheme) {
-        document.write(`<link rel="stylesheet" id="themeStyle" href="${newHref}">`);
-        window.currentTheme = document.getElementById("themeStyle");
-    } else if (newHref !== window.currentTheme.href) {
-        window.currentTheme.href = newHref;
+        const newHref = getVar("root-path") + newThemeName +
+            getVar("resource-suffix") + ".css";
+        if (!window.currentTheme) {
+            document.write(`<link rel="stylesheet" id="themeStyle" href="${newHref}">`);
+            window.currentTheme = document.getElementById("themeStyle");
+        } else if (newHref !== window.currentTheme.href) {
+            window.currentTheme.href = newHref;
+        }
     }
 }