XWIKI-23549: Support several CSS files in icon themes

* Allow several, comma-separated CSS files

Author: michitux

xwiki-platform-core/xwiki-platform-icon/xwiki-platform-icon-default/src/main/java/org/xwiki/icon/internal/DefaultIconRenderer.java

@@ -115,9 +115,14 @@ private void activeCSS(IconSet iconSet) throws IconException
     {
         String url = this.iconTemplateRendererManager.getRenderer(iconSet.getCss())
             .render(null, iconSet.getSourceDocumentReference());
-        Map<String, Object> parameters = new HashMap<>();
-        parameters.put("rel", "stylesheet");
-        this.linkExtension.use(url, parameters);
+        // Split URL at "," to support multiple CSS files.
+        // Commas in URLs are not that common, and if needed they can be encoded as %2C.
+        String[] urls = StringUtils.split(url, ',');
+        for (String cssUrl : urls) {
+            Map<String, Object> parameters = new HashMap<>();
+            parameters.put("rel", "stylesheet");
+            this.linkExtension.use(cssUrl, parameters);
+        }
     }
 
     private void activeSSX(IconSet iconSet)

xwiki-platform-core/xwiki-platform-icon/xwiki-platform-icon-default/src/test/java/org/xwiki/icon/internal/DefaultIconRendererTest.java

@@ -122,6 +122,35 @@ void renderWithCSS() throws Exception
         verify(this.jsExtension, never()).use(any());
     }
 
+    @Test
+    void renderWithMultipleCSS() throws Exception
+    {
+        IconSet iconSet = new IconSet("default");
+        String template = "image:$icon.png";
+        iconSet.setRenderWiki(template);
+        String css = "css1,css2";
+        iconSet.setCss(css);
+        iconSet.addIcon("test", new Icon("blabla"));
+
+        IconTemplateRenderer mockRenderer = mock();
+        when(this.rendererManager.getRenderer(css)).thenReturn(mockRenderer);
+        String parsedCSS = "velocityParsedCSS1,velocityParsedCSS2";
+        when(mockRenderer.render(null, null)).thenReturn(parsedCSS);
+
+        setupSimpleTemplate(template);
+
+        // Test
+        this.iconRenderer.render("test", iconSet);
+
+        // Verify
+        Map<String, Object> parameters = new HashMap<>();
+        parameters.put("rel", "stylesheet");
+        verify(this.linkExtension).use("velocityParsedCSS1", parameters);
+        verify(this.linkExtension).use("velocityParsedCSS2", parameters);
+        verify(this.skinExtension, never()).use(any());
+        verify(this.jsExtension, never()).use(any());
+    }
+
     @Test
     void renderWithSSX() throws Exception
     {