Replace the W3C computed-style cascade with internal types

Fold the ViewCSS/DocumentCSS machinery into the engine: CSSEngineImpl now
holds the stylesheet list and a cached flat rule list directly, and the
former ViewCSSImpl.getComputedStyle logic becomes CSSEngine.computeStyle.
The rule and stylesheet mirror drops its W3C interfaces: CSSStyleSheetImpl
is a plain list of CssRule (a new sealed interface), CSSStyleRuleImpl and
CSSImportRuleImpl are simple internal classes, and ViewCSSImpl,
DocumentCSSImpl, StyleSheetListImpl, CSSRuleImpl, CSSRuleListImpl,
MediaListImpl, AbstractCSSNode, ExtendedCSSRule, and ExtendedDocumentCSS
are deleted. CSSEngine.parseStyleSheet now returns the internal stylesheet
type and getDocumentCSS()/getViewCSS() are replaced by computeStyle; a
deprecated getViewCSS() default method remains as a binary-compatibility
bridge for bundles compiled against the old accessor.

CSSStyleDeclarationImpl keeps implementing the W3C CSSStyleDeclaration
interface because IStylingEngine.getStyle and IThemeEngine.getStyle are
frozen public API returning that type; its parent rule is now the internal
CSSStyleRuleImpl, reachable via getParentStyleRule(), and the W3C
getParentRule() returns null. In-tree callers (ThemeEngine, the font
handler, CSSRenderingUtils, PartRenderingEngine) and the css.core parser
tests move to the internal API.

Contributes to #3980

Author: vogella

bundles/org.eclipse.e4.ui.css.core/src/org/eclipse/e4/ui/css/core/dom/ExtendedCSSRule.java

@@ -20,16 +20,15 @@
 import org.eclipse.e4.ui.css.core.dom.IElementProvider;
 import org.eclipse.e4.ui.css.core.dom.properties.ICSSPropertyHandler;
 import org.eclipse.e4.ui.css.core.dom.properties.converters.ICSSValueConverter;
+import org.eclipse.e4.ui.css.core.impl.dom.CSSStyleSheetImpl;
 import org.eclipse.e4.ui.css.core.impl.engine.selector.Selectors;
 import org.eclipse.e4.ui.css.core.resources.IResourcesRegistry;
 import org.eclipse.e4.ui.css.core.util.resources.IResourcesLocatorManager;
 import org.w3c.dom.Element;
 import org.w3c.dom.css.CSSStyleDeclaration;
-import org.w3c.dom.css.CSSStyleSheet;
 import org.w3c.dom.css.CSSValue;
-import org.w3c.dom.css.DocumentCSS;
 import org.w3c.dom.css.ViewCSS;
-import org.w3c.dom.stylesheets.StyleSheet;
+import org.w3c.dom.views.DocumentView;
 
 /**
  * CSS Engine interface used to parse style sheet and apply styles to something
@@ -42,18 +41,18 @@ public interface CSSEngine {
 	/**
 	 * Parse style sheet from Reader reader.
 	 */
-	StyleSheet parseStyleSheet(Reader reader) throws IOException;
+	CSSStyleSheetImpl parseStyleSheet(Reader reader) throws IOException;
 
 	/**
 	 * Parse style sheet from InputStream stream.
 	 */
-	StyleSheet parseStyleSheet(InputStream stream) throws IOException;
+	CSSStyleSheetImpl parseStyleSheet(InputStream stream) throws IOException;
 
 	/**
 	 * Parse style sheet from InputStream stream, using {@code uri} as the base
 	 * location for resolving relative {@code @import} rules.
 	 */
-	StyleSheet parseStyleSheet(InputStream stream, String uri) throws IOException;
+	CSSStyleSheetImpl parseStyleSheet(InputStream stream, String uri) throws IOException;
 
 	/*--------------- Parse style declaration -----------------*/
 
@@ -184,17 +183,32 @@ public interface CSSEngine {
 	 */
 	IResourcesLocatorManager getResourcesLocatorManager();
 
-	/*--------------- Document/View CSS -----------------*/
+	/*--------------- Computed style -----------------*/
 
 	/**
-	 * Return the {@link DocumentCSS} used to store {@link CSSStyleSheet}.
+	 * Compute the merged style declaration for the given element and pseudo
+	 * element from all stylesheets registered with this engine.
 	 */
-	DocumentCSS getDocumentCSS();
+	CSSStyleDeclaration computeStyle(Element element, String pseudoElt);
 
 	/**
-	 * Return the {@link ViewCSS} used to compute {@link CSSStyleDeclaration}.
+	 * Binary-compatibility bridge for callers compiled against the removed
+	 * W3C cascade accessor; use {@link #computeStyle(Element, String)}.
 	 */
-	ViewCSS getViewCSS();
+	@Deprecated(forRemoval = true, since = "2026-06")
+	default ViewCSS getViewCSS() {
+		return new ViewCSS() {
+			@Override
+			public DocumentView getDocument() {
+				return null;
+			}
+
+			@Override
+			public CSSStyleDeclaration getComputedStyle(Element elt, String pseudoElt) {
+				return computeStyle(elt, pseudoElt);
+			}
+		};
+	}
 
 	/*--------------- w3c Element -----------------*/
 

bundles/org.eclipse.e4.ui.css.core/src/org/eclipse/e4/ui/css/core/dom/ExtendedDocumentCSS.java

@@ -37,7 +37,7 @@ public CSSComputedStyleImpl(List<StyleWrapper> styleRules) {
 		// only once after reading the stylesheet(s).
 		this.styleRules.sort(StyleWrapper.COMPARATOR);
 		for (StyleWrapper styleWrapper : this.styleRules) {
-			addCSSPropertyList(((CSSStyleDeclarationImpl) styleWrapper.style()).getCSSPropertyList());
+			addCSSPropertyList(styleWrapper.style().getCSSPropertyList());
 		}
 	}
 

bundles/org.eclipse.e4.ui.css.core/src/org/eclipse/e4/ui/css/core/engine/CSSEngine.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2008, 2015 Angelo Zerr and others.
+ * Copyright (c) 2008, 2026 Angelo Zerr and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -12,46 +12,26 @@
  *     Angelo Zerr <angelo.zerr@gmail.com> - initial API and implementation
  *     IBM Corporation - ongoing development
  *******************************************************************************/
-
 package org.eclipse.e4.ui.css.core.impl.dom;
 
-import org.w3c.dom.css.CSSImportRule;
-import org.w3c.dom.css.CSSRule;
-import org.w3c.dom.css.CSSStyleSheet;
-import org.w3c.dom.stylesheets.MediaList;
-
-public class CSSImportRuleImpl extends CSSRuleImpl implements CSSImportRule {
+/**
+ * An {@code @import} rule. The engine resolves and inlines the referenced
+ * stylesheet when the surrounding sheet is parsed.
+ */
+public final class CSSImportRuleImpl implements CssRule {
 
-	String uri;
-	MediaListImpl mediaList;
+	private final String href;
 
-	public CSSImportRuleImpl(CSSStyleSheet parentStyleSheet, CSSRule parentRule,
-			String uri, MediaListImpl mediaListImpl) {
-		super(parentStyleSheet, parentRule);
-		this.uri = uri;
-		this.mediaList = mediaListImpl;
-	}
-
-	@Override
-	public short getType() {
-		return CSSRule.IMPORT_RULE;
+	public CSSImportRuleImpl(String href) {
+		this.href = href;
 	}
 
-	// W3C CSSImportRule API methods
-
-	@Override
 	public String getHref() {
-		return uri;
-	}
-
-	@Override
-	public MediaList getMedia() {
-		return mediaList;
+		return href;
 	}
 
 	@Override
-	public CSSStyleSheet getStyleSheet() {
-		// TODO Auto-generated method stub
-		throw new UnsupportedOperationException("NOT YET IMPLEMENTED");
+	public String toString() {
+		return "@import url(" + href + ")"; //$NON-NLS-1$ //$NON-NLS-2$
 	}
-}
+}

bundles/org.eclipse.e4.ui.css.core/src/org/eclipse/e4/ui/css/core/impl/dom/CSSComputedStyleImpl.java

@@ -26,14 +26,14 @@
 import org.w3c.dom.css.CSSStyleDeclaration;
 import org.w3c.dom.css.CSSValue;
 
-public class CSSStyleDeclarationImpl extends AbstractCSSNode implements CSSStyleDeclaration {
+public class CSSStyleDeclarationImpl implements CSSStyleDeclaration {
 
 	private boolean readOnly;
-	private final CSSRule parentRule;
+	private final CSSStyleRuleImpl parentRule;
 	private final List<CSSProperty> properties = new ArrayList<>();
 	private CSSPropertyList cssPropertyListView;
 
-	public CSSStyleDeclarationImpl(CSSRule parentRule) {
+	public CSSStyleDeclarationImpl(CSSStyleRuleImpl parentRule) {
 		this.parentRule = parentRule;
 	}
 
@@ -61,6 +61,13 @@ public int getLength() {
 
 	@Override
 	public CSSRule getParentRule() {
+		// The internal rule model no longer implements the W3C CSSRule type;
+		// use getParentStyleRule() instead.
+		return null;
+	}
+
+	/** The style rule this declaration belongs to, or null for computed styles. */
+	public CSSStyleRuleImpl getParentStyleRule() {
 		return parentRule;
 	}