Added polyfill for var (moved from web_ui)

pkg/csslib/lib/src/polyfill.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of csslib.parser;
+
+/**
+ * CSS polyfill emits CSS to be understood by older parsers that which do not
+ * understand (var, calc, etc.).
+ */
+class PolyFill {
+  final Messages _messages;
+  final bool _warningsAsErrors;
+
+  Set<StyleSheet> allStyleSheets = new Set<StyleSheet>();
+
+  /**
+   * [_pseudoElements] list of known pseudo attributes found in HTML, any
+   * CSS pseudo-elements 'name::custom-element' is mapped to the manged name
+   * associated with the pseudo-element key.
+   */
+  PolyFill(this._messages, this._warningsAsErrors);
+
+  /**
+   * Run the analyzer on every file that is a style sheet or any component that
+   * has a style tag.
+   */
+  void process(StyleSheet stylesheet) {
+    // TODO(terry): Process all imported stylesheets.
+
+    var styleSheets = processVars([stylesheet]);
+    allStyleSheets.addAll(styleSheets);
+
+    normalize();
+  }
+
+  void normalize() {
+    // Remove all var definitions for all style sheets analyzed.
+    for (var tree in allStyleSheets)
+      new _RemoveVarDefinitions().visitTree(tree);
+  }
+
+  List<StyleSheet> processVars(List<StyleSheet> styleSheets) {
+    // TODO(terry): Process all dependencies.
+    // Build list of all var definitions.
+    Map varDefs = new Map();
+    for (var tree in styleSheets) {
+      var allDefs = (new _VarDefinitions()..visitTree(tree)).found;
+      allDefs.forEach((key, value) {
+        varDefs[key] = value;
+      });
+    }
+
+    // Resolve all definitions to a non-VarUsage (terminal expression).
+    varDefs.forEach((key, value) {
+      for (var expr in (value.expression as Expressions).expressions) {
+        var def = _findTerminalVarDefinition(varDefs, value);
+        varDefs[key] = def;
+      }
+    });
+
+    // Resolve all var usages.
+    for (var tree in styleSheets) {
+      new _ResolveVarUsages(varDefs).visitTree(tree);
+    }
+
+    return styleSheets;
+  }
+}
+
+/**
+ * Find var- definitions in a style sheet.
+ * [found] list of known definitions.
+ */
+class _VarDefinitions extends Visitor {
+  final Map<String, VarDefinition> found = new Map();
+
+  void visitTree(StyleSheet tree) {
+    visitStyleSheet(tree);
+  }
+
+  visitVarDefinition(VarDefinition node) {
+    // Replace with latest variable definition.
+    found[node.definedName] = node;
+    super.visitVarDefinition(node);
+  }
+
+  void visitVarDefinitionDirective(VarDefinitionDirective node) {
+    visitVarDefinition(node.def);
+  }
+}
+
+/**
+ * Resolve any CSS expression which contains a var() usage to the ultimate real
+ * CSS expression value e.g.,
+ *
+ *    var-one: var(two);
+ *    var-two: #ff00ff;
+ *
+ *    .test {
+ *      color: var(one);
+ *    }
+ *
+ * then .test's color would be #ff00ff
+ */
+class _ResolveVarUsages extends Visitor {
+  final Map<String, VarDefinition> varDefs;
+  bool inVarDefinition = false;
+  bool inUsage = false;
+  Expressions currentExpressions;
+
+  _ResolveVarUsages(this.varDefs);
+
+  void visitTree(StyleSheet tree) {
+    visitStyleSheet(tree);
+  }
+
+  void visitVarDefinition(VarDefinition varDef) {
+    inVarDefinition = true;
+    super.visitVarDefinition(varDef);
+    inVarDefinition = false;
+  }
+
+  void visitExpressions(Expressions node) {
+    currentExpressions = node;
+    super.visitExpressions(node);
+    currentExpressions = null;
+  }
+
+  void visitVarUsage(VarUsage node) {
+    // Don't process other var() inside of a varUsage.  That implies that the
+    // default is a var() too.  Also, don't process any var() inside of a
+    // varDefinition (they're just place holders until we've resolved all real
+    // usages.
+    if (!inUsage && !inVarDefinition && currentExpressions != null) {
+      var expressions = currentExpressions.expressions;
+      var index = expressions.indexOf(node);
+      assert(index >= 0);
+      var def = varDefs[node.name];
+      if (def != null) {
+        // Found a VarDefinition use it.
+        _resolveVarUsage(currentExpressions.expressions, index, def);
+      } else if (node.defaultValues.any((e) => e is VarUsage)) {
+        // Don't have a VarDefinition need to use default values resolve all
+        // default values.
+        var terminalDefaults = [];
+        for (var defaultValue in node.defaultValues) {
+          terminalDefaults.addAll(resolveUsageTerminal(defaultValue));
+        }
+        expressions.replaceRange(index, index + 1, terminalDefaults);
+      } else {
+        // No VarDefinition but default value is a terminal expression; use it.
+        expressions.replaceRange(index, index + 1, node.defaultValues);
+      }
+    }
+
+    inUsage = true;
+    super.visitVarUsage(node);
+    inUsage = false;
+  }
+
+  List<Expression> resolveUsageTerminal(VarUsage usage) {
+    var result = [];
+
+    var varDef = varDefs[usage.name];
+    var expressions;
+    if (varDef == null) {
+      // VarDefinition not found try the defaultValues.
+      expressions = usage.defaultValues;
+    } else {
+      // Use the VarDefinition found.
+      expressions = (varDef.expression as Expressions).expressions;
+    }
+
+    for (var expr in expressions) {
+      if (expr is VarUsage) {
+        // Get terminal value.
+        result.addAll(resolveUsageTerminal(expr));
+      }
+    }
+
+    // We're at a terminal just return the VarDefinition expression.
+    if (result.isEmpty && varDef != null) {
+      result = (varDef.expression as Expressions).expressions;
+    }
+
+    return result;
+  }
+
+  _resolveVarUsage(List<Expressions> expressions, int index,
+                   VarDefinition def) {
+    var defExpressions = (def.expression as Expressions).expressions;
+    expressions.replaceRange(index, index + 1, defExpressions);
+  }
+}
+
+/** Remove all var definitions. */
+class _RemoveVarDefinitions extends Visitor {
+  void visitTree(StyleSheet tree) {
+    visitStyleSheet(tree);
+  }
+
+  void visitStyleSheet(StyleSheet ss) {
+    ss.topLevels.removeWhere((e) => e is VarDefinitionDirective);
+    super.visitStyleSheet(ss);
+  }
+
+  void visitDeclarationGroup(DeclarationGroup node) {
+    node.declarations.removeWhere((e) => e is VarDefinition);
+    super.visitDeclarationGroup(node);
+  }
+}
+
+/** Find terminal definition (non VarUsage implies real CSS value). */
+VarDefinition _findTerminalVarDefinition(Map<String, VarDefinition> varDefs,
+    VarDefinition varDef) {
+  var expressions = varDef.expression as Expressions;
+  for (var expr in expressions.expressions) {
+    if (expr is VarUsage) {
+      var usageName = (expr as VarUsage).name;
+      var foundDef = varDefs[usageName];
+
+      // If foundDef is unknown check if defaultValues; if it exist then resolve
+      // to terminal value.
+      if (foundDef == null) {
+        // We're either a VarUsage or terminal definition if in varDefs;
+        // either way replace VarUsage with it's default value because the
+        // VarDefinition isn't found.
+        var defaultValues = (expr as VarUsage).defaultValues;
+        var replaceExprs = expressions.expressions;
+        assert(replaceExprs.length == 1);
+        replaceExprs.replaceRange(0, 1, defaultValues);
+        return varDef;
+      }
+      if (foundDef is VarDefinition) {
+        return _findTerminalVarDefinition(varDefs, foundDef);
+      }
+    } else {
+      // Return real CSS property.
+      return varDef;
+    }
+  }
+
+  // Didn't point to a var definition that existed.
+  return varDef;
+}