source: branches/PersistentDataStructures/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory.CSharp-5.5.0/OutputVisitor/InsertParenthesesVisitor.cs

// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
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// 
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// 
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using System;

namespace ICSharpCode.NRefactory.CSharp
{
  /// <summary>
  /// Inserts the parentheses into the AST that are needed to ensure the AST can be printed correctly.
  /// For example, if the AST contains
  /// BinaryOperatorExpresson(2, Mul, BinaryOperatorExpression(1, Add, 1))); printing that AST
  /// would incorrectly result in "2 * 1 + 1". By running InsertParenthesesVisitor, the necessary
  /// parentheses are inserted: "2 * (1 + 1)".
  /// </summary>
  public class InsertParenthesesVisitor : DepthFirstAstVisitor
  {
    /// <summary>
    /// Gets/Sets whether the visitor should insert parentheses to make the code better looking.
    /// If this property is false, it will insert parentheses only where strictly required by the language spec.
    /// </summary>
    public bool InsertParenthesesForReadability { get; set; }
    
    const int Primary = 16;
    const int QueryOrLambda = 15;
    const int Unary = 14;
    const int RelationalAndTypeTesting = 10;
    const int Equality = 9;
    const int Conditional = 2;
    const int Assignment = 1;
    
    /// <summary>
    /// Gets the row number in the C# 4.0 spec operator precedence table.
    /// </summary>
    static int GetPrecedence(Expression expr)
    {
      // Note: the operator precedence table on MSDN is incorrect
      if (expr is QueryExpression) {
        // Not part of the table in the C# spec, but we need to ensure that queries within
        // primary expressions get parenthesized.
        return QueryOrLambda;
      }
      UnaryOperatorExpression uoe = expr as UnaryOperatorExpression;
      if (uoe != null) {
        if (uoe.Operator == UnaryOperatorType.PostDecrement || uoe.Operator == UnaryOperatorType.PostIncrement)
          return Primary;
        else
          return Unary;
      }
      if (expr is CastExpression)
        return Unary;
      BinaryOperatorExpression boe = expr as BinaryOperatorExpression;
      if (boe != null) {
        switch (boe.Operator) {
          case BinaryOperatorType.Multiply:
          case BinaryOperatorType.Divide:
          case BinaryOperatorType.Modulus:
            return 13; // multiplicative
          case BinaryOperatorType.Add:
          case BinaryOperatorType.Subtract:
            return 12; // additive
          case BinaryOperatorType.ShiftLeft:
          case BinaryOperatorType.ShiftRight:
            return 11;
          case BinaryOperatorType.GreaterThan:
          case BinaryOperatorType.GreaterThanOrEqual:
          case BinaryOperatorType.LessThan:
          case BinaryOperatorType.LessThanOrEqual:
            return RelationalAndTypeTesting;
          case BinaryOperatorType.Equality:
          case BinaryOperatorType.InEquality:
            return Equality;
          case BinaryOperatorType.BitwiseAnd:
            return 8;
          case BinaryOperatorType.ExclusiveOr:
            return 7;
          case BinaryOperatorType.BitwiseOr:
            return 6;
          case BinaryOperatorType.ConditionalAnd:
            return 5;
          case BinaryOperatorType.ConditionalOr:
            return 4;
          case BinaryOperatorType.NullCoalescing:
            return 3;
          default:
            throw new NotSupportedException("Invalid value for BinaryOperatorType");
        }
      }
      if (expr is IsExpression || expr is AsExpression)
        return RelationalAndTypeTesting;
      if (expr is ConditionalExpression)
        return Conditional;
      if (expr is AssignmentExpression || expr is LambdaExpression)
        return Assignment;
      // anything else: primary expression
      return Primary;
    }
    
    /// <summary>
    /// Parenthesizes the expression if it does not have the minimum required precedence.
    /// </summary>
    static void ParenthesizeIfRequired(Expression expr, int minimumPrecedence)
    {
      if (GetPrecedence(expr) < minimumPrecedence) {
        Parenthesize(expr);
      }
    }

    static void Parenthesize(Expression expr)
    {
      expr.ReplaceWith(e => new ParenthesizedExpression { Expression = e });
    }
    
    // Primary expressions
    public override void VisitMemberReferenceExpression(MemberReferenceExpression memberReferenceExpression)
    {
      ParenthesizeIfRequired(memberReferenceExpression.Target, Primary);
      base.VisitMemberReferenceExpression(memberReferenceExpression);
    }
    
    public override void VisitPointerReferenceExpression(PointerReferenceExpression pointerReferenceExpression)
    {
      ParenthesizeIfRequired(pointerReferenceExpression.Target, Primary);
      base.VisitPointerReferenceExpression(pointerReferenceExpression);
    }
    
    public override void VisitInvocationExpression(InvocationExpression invocationExpression)
    {
      ParenthesizeIfRequired(invocationExpression.Target, Primary);
      base.VisitInvocationExpression(invocationExpression);
    }
    
    public override void VisitIndexerExpression(IndexerExpression indexerExpression)
    {
      ParenthesizeIfRequired(indexerExpression.Target, Primary);
      ArrayCreateExpression ace = indexerExpression.Target as ArrayCreateExpression;
      if (ace != null && (InsertParenthesesForReadability || ace.Initializer.IsNull)) {
        // require parentheses for "(new int[1])[0]"
        Parenthesize(indexerExpression.Target);
      }
      base.VisitIndexerExpression(indexerExpression);
    }
    
    // Unary expressions
    public override void VisitUnaryOperatorExpression(UnaryOperatorExpression unaryOperatorExpression)
    {
      ParenthesizeIfRequired(unaryOperatorExpression.Expression, GetPrecedence(unaryOperatorExpression));
      UnaryOperatorExpression child = unaryOperatorExpression.Expression as UnaryOperatorExpression;
      if (child != null && InsertParenthesesForReadability)
        Parenthesize(child);
      base.VisitUnaryOperatorExpression(unaryOperatorExpression);
    }
    
    public override void VisitCastExpression(CastExpression castExpression)
    {
      ParenthesizeIfRequired(castExpression.Expression, InsertParenthesesForReadability ? Primary : Unary);
      // There's a nasty issue in the C# grammar: cast expressions including certain operators are ambiguous in some cases
      // "(int)-1" is fine, but "(A)-b" is not a cast.
      UnaryOperatorExpression uoe = castExpression.Expression as UnaryOperatorExpression;
      if (uoe != null && !(uoe.Operator == UnaryOperatorType.BitNot || uoe.Operator == UnaryOperatorType.Not)) {
        if (TypeCanBeMisinterpretedAsExpression(castExpression.Type)) {
          Parenthesize(castExpression.Expression);
        }
      }
      // The above issue can also happen with PrimitiveExpressions representing negative values:
      PrimitiveExpression pe = castExpression.Expression as PrimitiveExpression;
      if (pe != null && pe.Value != null && TypeCanBeMisinterpretedAsExpression(castExpression.Type)) {
        TypeCode typeCode = Type.GetTypeCode(pe.Value.GetType());
        switch (typeCode) {
          case TypeCode.SByte:
            if ((sbyte)pe.Value < 0)
              Parenthesize(castExpression.Expression);
            break;
          case TypeCode.Int16:
            if ((short)pe.Value < 0)
              Parenthesize(castExpression.Expression);
            break;
          case TypeCode.Int32:
            if ((int)pe.Value < 0)
              Parenthesize(castExpression.Expression);
            break;
          case TypeCode.Int64:
            if ((long)pe.Value < 0)
              Parenthesize(castExpression.Expression);
            break;
          case TypeCode.Single:
            if ((float)pe.Value < 0)
              Parenthesize(castExpression.Expression);
            break;
          case TypeCode.Double:
            if ((double)pe.Value < 0)
              Parenthesize(castExpression.Expression);
            break;
          case TypeCode.Decimal:
            if ((decimal)pe.Value < 0)
              Parenthesize(castExpression.Expression);
            break;
        }
      }
      base.VisitCastExpression(castExpression);
    }
    
    static bool TypeCanBeMisinterpretedAsExpression(AstType type)
    {
      // SimpleTypes can always be misinterpreted as IdentifierExpressions
      // MemberTypes can be misinterpreted as MemberReferenceExpressions if they don't use double colon
      // PrimitiveTypes or ComposedTypes can never be misinterpreted as expressions.
      MemberType mt = type as MemberType;
      if (mt != null)
        return !mt.IsDoubleColon;
      else
        return type is SimpleType;
    }
    
    // Binary Operators
    public override void VisitBinaryOperatorExpression(BinaryOperatorExpression binaryOperatorExpression)
    {
      int precedence = GetPrecedence(binaryOperatorExpression);
      if (binaryOperatorExpression.Operator == BinaryOperatorType.NullCoalescing) {
        if (InsertParenthesesForReadability) {
          ParenthesizeIfRequired(binaryOperatorExpression.Left, Primary);
          ParenthesizeIfRequired(binaryOperatorExpression.Right, Primary);
        } else {
          // ?? is right-associative
          ParenthesizeIfRequired(binaryOperatorExpression.Left, precedence + 1);
          ParenthesizeIfRequired(binaryOperatorExpression.Right, precedence);
        }
      } else {
        if (InsertParenthesesForReadability && precedence < Equality) {
          // In readable mode, boost the priority of the left-hand side if the operator
          // there isn't the same as the operator on this expression.
          if (GetBinaryOperatorType(binaryOperatorExpression.Left) == binaryOperatorExpression.Operator) {
            ParenthesizeIfRequired(binaryOperatorExpression.Left, precedence);
          } else {
            ParenthesizeIfRequired(binaryOperatorExpression.Left, Equality);
          }
          ParenthesizeIfRequired(binaryOperatorExpression.Right, Equality);
        } else {
          // all other binary operators are left-associative
          ParenthesizeIfRequired(binaryOperatorExpression.Left, precedence);
          ParenthesizeIfRequired(binaryOperatorExpression.Right, precedence + 1);
        }
      }
      base.VisitBinaryOperatorExpression(binaryOperatorExpression);
    }
    
    BinaryOperatorType? GetBinaryOperatorType(Expression expr)
    {
      BinaryOperatorExpression boe = expr as BinaryOperatorExpression;
      if (boe != null)
        return boe.Operator;
      else
        return null;
    }
    
    public override void VisitIsExpression(IsExpression isExpression)
    {
      if (InsertParenthesesForReadability) {
        // few people know the precedence of 'is', so always put parentheses in nice-looking mode.
        ParenthesizeIfRequired(isExpression.Expression, Primary);
      } else {
        ParenthesizeIfRequired(isExpression.Expression, RelationalAndTypeTesting);
      }
      base.VisitIsExpression(isExpression);
    }
    
    public override void VisitAsExpression(AsExpression asExpression)
    {
      if (InsertParenthesesForReadability) {
        // few people know the precedence of 'as', so always put parentheses in nice-looking mode.
        ParenthesizeIfRequired(asExpression.Expression, Primary);
      } else {
        ParenthesizeIfRequired(asExpression.Expression, RelationalAndTypeTesting);
      }
      base.VisitAsExpression(asExpression);
    }
    
    // Conditional operator
    public override void VisitConditionalExpression(ConditionalExpression conditionalExpression)
    {
      // Associativity here is a bit tricky:
      // (a ? b : c ? d : e) == (a ? b : (c ? d : e))
      // (a ? b ? c : d : e) == (a ? (b ? c : d) : e)
      // Only ((a ? b : c) ? d : e) strictly needs the additional parentheses
      if (InsertParenthesesForReadability) {
        // Precedence of ?: can be confusing; so always put parentheses in nice-looking mode.
        ParenthesizeIfRequired(conditionalExpression.Condition, Primary);
        ParenthesizeIfRequired(conditionalExpression.TrueExpression, Primary);
        ParenthesizeIfRequired(conditionalExpression.FalseExpression, Primary);
      } else {
        ParenthesizeIfRequired(conditionalExpression.Condition, Conditional + 1);
        ParenthesizeIfRequired(conditionalExpression.TrueExpression, Conditional);
        ParenthesizeIfRequired(conditionalExpression.FalseExpression, Conditional);
      }
      base.VisitConditionalExpression(conditionalExpression);
    }
    
    public override void VisitAssignmentExpression(AssignmentExpression assignmentExpression)
    {
      // assignment is right-associative
      ParenthesizeIfRequired(assignmentExpression.Left, Assignment + 1);
      if (InsertParenthesesForReadability) {
        ParenthesizeIfRequired(assignmentExpression.Right, RelationalAndTypeTesting + 1);
      } else {
        ParenthesizeIfRequired(assignmentExpression.Right, Assignment);
      }
      base.VisitAssignmentExpression(assignmentExpression);
    }
    
    // don't need to handle lambdas, they have lowest precedence and unambiguous associativity
    
    public override void VisitQueryExpression(QueryExpression queryExpression)
    {
      // Query expressions are strange beasts:
      // "var a = -from b in c select d;" is valid, so queries bind stricter than unary expressions.
      // However, the end of the query is greedy. So their start sort of has a high precedence,
      // while their end has a very low precedence. We handle this by checking whether a query is used
      // as left part of a binary operator, and parenthesize it if required.
      if (queryExpression.Role == BinaryOperatorExpression.LeftRole)
        Parenthesize(queryExpression);
      if (queryExpression.Parent is IsExpression || queryExpression.Parent is AsExpression)
        Parenthesize(queryExpression);
      if (InsertParenthesesForReadability) {
        // when readability is desired, always parenthesize query expressions within unary or binary operators
        if (queryExpression.Parent is UnaryOperatorExpression || queryExpression.Parent is BinaryOperatorExpression)
          Parenthesize(queryExpression);
      }
      base.VisitQueryExpression(queryExpression);
    }
  }
}