SharpDevelop/ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/VariableDeclaredInWideScopeIssue.cs

//
// VariableDeclaredWideScopeIssue.cs
//
// Author:
//       Simon Lindgren <simon.n.lindgren@gmail.com>
//
// Copyright (c) 2012 Simon Lindgren
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
using System.Collections.Generic;
using System.Linq;
using System;
using ICSharpCode.NRefactory.Semantics;
using ICSharpCode.NRefactory.TypeSystem;
using ICSharpCode.NRefactory.Refactoring;

namespace ICSharpCode.NRefactory.CSharp.Refactoring
{
//	[IssueDescription("The variable can be declared in a nested scope",
//	                   Description = "Highlights variables that can be declared in a nested scope.",
//	                   Category = IssueCategories.Opportunities,
//	                   Severity = Severity.Suggestion)]
	public class VariableDeclaredInWideScopeIssue : ICodeIssueProvider
	{
		#region ICodeIssueProvider implementation
		public IEnumerable<CodeIssue> GetIssues(BaseRefactoringContext context)
		{
			return new GatherVisitor(context, this).GetIssues();
		}
		#endregion

		class GatherVisitor : GatherVisitorBase<VariableDeclaredInWideScopeIssue>
		{
			readonly BaseRefactoringContext context;
			
			public GatherVisitor(BaseRefactoringContext context, VariableDeclaredInWideScopeIssue issueProvider) : base (context, issueProvider)
			{
				this.context = context;
			}

			static readonly IList<Type> moveTargetBlacklist = new List<Type> {
				typeof(WhileStatement),
				typeof(ForeachStatement),
				typeof(ForStatement),
				typeof(DoWhileStatement),
				typeof(TryCatchStatement),
				typeof(AnonymousMethodExpression),
				typeof(LambdaExpression),
				typeof(LockStatement)
			};

			class CheckInitializer : DepthFirstAstVisitor
			{
				public bool IsValid {
					get;
					private set;
				}

				public CheckInitializer()
				{
					IsValid = true;
				}

				public override void VisitInvocationExpression(InvocationExpression invocationExpression)
				{
					base.VisitInvocationExpression(invocationExpression);
					IsValid = false;
				}
			}
			
			bool CheckForInvocations(Expression initializer)
			{
				var visitor = new CheckInitializer();
				initializer.AcceptVisitor(visitor);
				return visitor.IsValid;
			}

			public override void VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement)
			{
				base.VisitVariableDeclarationStatement(variableDeclarationStatement);

				var rootNode = variableDeclarationStatement.Parent as BlockStatement;
				if (rootNode == null)
					// We are somewhere weird, like a the ResourceAquisition of a using statement
					return;

				// TODO: Handle declarations with more than one variable?
				if (variableDeclarationStatement.Variables.Count > 1)
					return;

				var variableInitializer = variableDeclarationStatement.Variables.First();
				var identifiers = GetIdentifiers(rootNode.Descendants, variableInitializer.Name).ToList();

				if (identifiers.Count == 0)
					// variable is not used
					return;

				if (!CheckForInvocations(variableInitializer.Initializer))
					return;

				AstNode deepestCommonAncestor = GetDeepestCommonAncestor(rootNode, identifiers);
				var path = GetPath(rootNode, deepestCommonAncestor);

				// The node that will follow the moved declaration statement
				AstNode anchorNode = GetInitialAnchorNode(rootNode, identifiers, path);

				// Restrict path to only those where the initializer has not changed
				var pathToCheck = path.Skip(1).ToList();
				var firstInitializerChangeNode = GetFirstInitializerChange(variableDeclarationStatement, pathToCheck, variableInitializer.Initializer);
				if (firstInitializerChangeNode != null) {
					// The node changing the initializer expression may not be on the path
					// to the actual usages of the variable, so we need to merge the paths
					// so we get the part of the paths that are common between them
					var pathToChange = GetPath(rootNode, firstInitializerChangeNode);
					var deepestCommonIndex = GetLowestCommonAncestorIndex(path, pathToChange);
					anchorNode = pathToChange [deepestCommonIndex + 1];
					path = pathToChange.Take(deepestCommonIndex).ToList();
				}

				// Restrict to locations outside of blacklisted node types
				var firstBlackListedNode = path.Where(node => moveTargetBlacklist.Contains(node.GetType())).FirstOrDefault();
				if (firstBlackListedNode != null) {
					path = GetPath(rootNode, firstBlackListedNode.Parent);
					anchorNode = firstBlackListedNode;
				}

				anchorNode = GetInsertionPoint(anchorNode);

				if (anchorNode != null && anchorNode != rootNode && anchorNode.Parent != rootNode) {
					AddIssue(variableDeclarationStatement, context.TranslateString("Variable could be moved to a nested scope"),
					         GetActions(variableDeclarationStatement, (Statement)anchorNode));
				}
			}

			static bool IsBannedInsertionPoint(AstNode anchorNode)
			{
				var parent = anchorNode.Parent;

				// Don't split 'else if ...' into else { if ... }
				if (parent is IfElseStatement && anchorNode is IfElseStatement)
					return true;
				// Don't allow moving the declaration into the resource aquisition of a using statement
				if (parent is UsingStatement)
					return true;
				// Don't allow moving things into arbitrary positions of for statements
				if (parent is ForStatement && anchorNode.Role != Roles.EmbeddedStatement)
					return true;
				return false;
			}

			static AstNode GetInsertionPoint(AstNode node)
			{
				while (true) {
					if (node == null)
						break;
					if (node is Statement && !IsBannedInsertionPoint(node))
						break;
					node = node.Parent;
				}
				return node;
			}

			AstNode GetInitialAnchorNode (BlockStatement rootNode, List<IdentifierExpression> identifiers, IList<AstNode> path)
			{
				if (identifiers.Count > 1) {
					// Assume the first identifier is the first in the execution flow
					// firstPath will always be longer than path since path is the
					// combination of a least two (different) paths.
					var firstPath = GetPath(rootNode, identifiers [0]);
					if (firstPath [path.Count].Role == IfElseStatement.TrueRole) {
						// IfElseStatement has a slightly weird structure; Don't
						// consider the true role eligible for anchor node in this case
						return firstPath [path.Count - 1];
					}
					return firstPath [path.Count];
				}
				// We only have one path, and a statement in itself cannot be an identifier
				// so we're safe
				return path [path.Count - 1];
			}

			static IEnumerable<IdentifierExpression> GetIdentifiers(IEnumerable<AstNode> candidates, string name = null)
			{
				return 
					from node in candidates
					let identifier = node as IdentifierExpression
					where identifier != null && (name == null || identifier.Identifier == name)
					select identifier;
			}

			AstNode GetFirstInitializerChange(AstNode variableDeclarationStatement, IList<AstNode> path, Expression initializer)
			{
				var identifiers = GetIdentifiers(initializer.DescendantsAndSelf).ToList();
				var mayChangeInitializer = GetChecker (initializer, identifiers);
				AstNode lastChange = null;
				for (int i = path.Count - 1; i >= 0; i--) {
					for (AstNode node = path[i].PrevSibling; node != null && node != variableDeclarationStatement; node = node.PrevSibling) {
						// Special case for IfElseStatement: The AST nesting does not match the scope nesting, so
						// don't handle branches here: The correct one has already been checked anyway.
						// This also works to our advantage: No special checking is needed for the condition since
						// it is a the same level in the tree as the false branch
						if (node.Role == IfElseStatement.TrueRole || node.Role == IfElseStatement.FalseRole)
							continue;
						foreach (var expression in node.DescendantsAndSelf.Where(n => n is Expression).Cast<Expression>()) {
							if (mayChangeInitializer(expression)) {
								lastChange = expression;
							}
						}
					}
				}
				return lastChange;
			}

			Func<Expression, bool> GetChecker(Expression expression, IList<IdentifierExpression> identifiers)
			{
				// TODO: This only works for simple cases.
				IList<IMember> members;
				IList<IVariable> locals;
				var identifierResolveResults = identifiers.Select(identifier => context.Resolve(identifier)).ToList();
				SplitResolveResults(identifierResolveResults, out members, out locals);
				
				if (expression is InvocationExpression || expression is ObjectCreateExpression) {
					return node => {
						if (node is InvocationExpression || node is ObjectCreateExpression)
							// We don't know what these might do, so assume it will change the initializer
							return true;
						var binaryOperator = node as BinaryOperatorExpression;
						if (binaryOperator != null) {
							var resolveResult = context.Resolve(binaryOperator) as OperatorResolveResult;
							if (resolveResult == null)
								return false;
							// Built-in operators are ok, user defined ones not so much
							return resolveResult.UserDefinedOperatorMethod != null;
						}
						return IsConflictingAssignment(node, identifiers, members, locals);
					};
				} else if (expression is IdentifierExpression) {
					var initializerDependsOnMembers = identifierResolveResults.Any(result => result is MemberResolveResult);
					var initializerDependsOnReferenceType = identifierResolveResults.Any(result => result.Type.IsReferenceType == true);
					return node => {
						if ((node is InvocationExpression || node is ObjectCreateExpression) &&
						    (initializerDependsOnMembers || initializerDependsOnReferenceType))
							// Anything can happen...
							return true;
						var binaryOperator = node as BinaryOperatorExpression;
						if (binaryOperator != null) {
							var resolveResult = context.Resolve(binaryOperator) as OperatorResolveResult;
							if (resolveResult == null)
								return false;
							return resolveResult.UserDefinedOperatorMethod != null;
						}
						return IsConflictingAssignment(node, identifiers, members, locals);
					};
				}

				return node => false;
			}

			bool IsConflictingAssignment (Expression node, IList<IdentifierExpression> identifiers, IList<IMember> members, IList<IVariable> locals)
			{
				var assignmentExpression = node as AssignmentExpression;
				if (assignmentExpression != null) {
					IList<IMember> targetMembers;
					IList<IVariable> targetLocals;
					var identifierResolveResults = identifiers.Select(identifier => context.Resolve(identifier)).ToList();
					SplitResolveResults(identifierResolveResults, out targetMembers, out targetLocals);

					return members.Any(member => targetMembers.Contains(member)) ||
						locals.Any(local => targetLocals.Contains(local));
				}
				return false;
			}

			static void SplitResolveResults(List<ResolveResult> identifierResolveResults, out IList<IMember> members, out IList<IVariable> locals)
			{
				members = new List<IMember>();
				locals = new List<IVariable>();
				foreach (var resolveResult in identifierResolveResults) {
					var memberResolveResult = resolveResult as MemberResolveResult;
					if (memberResolveResult != null) {
						members.Add(memberResolveResult.Member);
					}
					var localResolveResult = resolveResult as LocalResolveResult;
					if (localResolveResult != null) {
						locals.Add(localResolveResult.Variable);
					}
				}
			}

			bool IsScopeContainer(AstNode node)
			{
				if (node == null)
					return false;

				var blockStatement = node as BlockStatement;
				if (blockStatement != null)
					return true;

				var statement = node as Statement;
				if (statement == null)
					return false;

				var role = node.Role;
				if (role == Roles.EmbeddedStatement ||
					role == IfElseStatement.TrueRole ||
					role == IfElseStatement.FalseRole) {
					return true;
				}
				return false;
			}

			IEnumerable<CodeAction> GetActions(Statement oldStatement, Statement followingStatement)
			{
				yield return new CodeAction(context.TranslateString("Move to nested scope"), script => {
					var parent = followingStatement.Parent;
					if (parent is SwitchSection || parent is BlockStatement) {
						script.InsertBefore(followingStatement, oldStatement.Clone());
					} else {
						var newBlockStatement = new BlockStatement {
							Statements = {
								oldStatement.Clone(),
								followingStatement.Clone()
							}
						};
						script.Replace(followingStatement, newBlockStatement);
						script.FormatText(parent);
					}
					script.Remove(oldStatement);
				}, oldStatement);
			}

			AstNode GetDeepestCommonAncestor(AstNode assumedRoot, IEnumerable<AstNode> leaves)
			{
				var previousPath = GetPath(assumedRoot, leaves.First());
				int lowestIndex = previousPath.Count - 1;
				foreach (var leaf in leaves.Skip(1)) {
					var currentPath = GetPath(assumedRoot, leaf);
					lowestIndex = GetLowestCommonAncestorIndex(previousPath, currentPath, lowestIndex);
					previousPath = currentPath;
				}
				return previousPath [lowestIndex];
			}
			
			int GetLowestCommonAncestorIndex(IList<AstNode> path1, IList<AstNode> path2, int maxIndex = int.MaxValue)
			{
				var max = Math.Min(Math.Min(path1.Count, path2.Count), maxIndex);
				for (int i = 0; i <= max; i++) {
					if (path1 [i] != path2 [i])
						return i - 1;
				}
				return max;
			}

			IList<AstNode> GetPath(AstNode from, AstNode to)
			{
				var reversePath = new List<AstNode>();
				do {
					reversePath.Add(to);
					to = to.Parent;
				} while (to != from.Parent);
				reversePath.Reverse();
				return reversePath;
			}
		}
	}
}