source: branches/2434_crossvalidation/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory.CSharp-5.5.0/Resolver/DetectSkippableNodesNavigator.cs

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using System;
using System.Collections.Generic;
using ICSharpCode.NRefactory.Semantics;
using ICSharpCode.NRefactory.TypeSystem;

namespace ICSharpCode.NRefactory.CSharp.Resolver
{
  /// <summary>
  /// When an <see cref="IResolveVisitorNavigator"/> is searching for specific nodes
  /// (e.g. all IdentifierExpressions), it has to scan the whole syntax tree for those nodes.
  /// However, scanning in the ResolveVisitor is expensive (e.g. any lambda that is scanned must be resolved),
  /// so it makes sense to detect when a whole subtree is scan-only, and skip that tree instead.
  /// 
  /// The DetectSkippableNodesNavigator performs this job by running the input IResolveVisitorNavigator
  /// over the whole AST, and detecting subtrees that are scan-only, and replaces them with Skip.
  /// </summary>
  public sealed class DetectSkippableNodesNavigator : IResolveVisitorNavigator
  {
    readonly Dictionary<AstNode, ResolveVisitorNavigationMode> dict = new Dictionary<AstNode, ResolveVisitorNavigationMode>();
    IResolveVisitorNavigator navigator;
    
    public DetectSkippableNodesNavigator(IResolveVisitorNavigator navigator, AstNode root)
    {
      this.navigator = navigator;
      Init(root);
    }
    
    bool Init(AstNode node)
    {
      var mode = navigator.Scan(node);
      if (mode == ResolveVisitorNavigationMode.Skip)
        return false;
      
      bool needsResolve = (mode != ResolveVisitorNavigationMode.Scan);
      
      for (AstNode child = node.FirstChild; child != null; child = child.NextSibling) {
        needsResolve |= Init(child);
      }
      
      if (needsResolve) {
        // If this node or any child node needs resolving, store the mode in the dictionary.
        dict.Add(node, mode);
      }
      return needsResolve;
    }
    
    /// <inheritdoc/>
    public ResolveVisitorNavigationMode Scan(AstNode node)
    {
      ResolveVisitorNavigationMode mode;
      if (dict.TryGetValue(node, out mode)) {
        return mode;
      } else {
        return ResolveVisitorNavigationMode.Skip;
      }
    }
    
    /// <inheritdoc/>
    public void Resolved(AstNode node, ResolveResult result)
    {
      navigator.Resolved(node, result);
    }
    
    /// <inheritdoc/>
    public void ProcessConversion(Expression expression, ResolveResult result, Conversion conversion, IType targetType)
    {
      navigator.ProcessConversion(expression, result, conversion, targetType);
    }
  }
}