[GH-138] - introduce substitute refactoring

documentation/README.md

@@ -6,3 +6,11 @@ See [rules list](rules/README.md).
 
 * [Configuration](Configuration.md)
 * [Visual Studio compatibility](Compatibility.md)
+
+### Code refactoring
+
+#### Introduce substitute
+
+Automatically create substitutes for constructor arguments as fields or local variables.
+![introducesubstitutecsharp](https://user-images.githubusercontent.com/7378346/77374918-54832d80-6d6c-11ea-965a-eb96080bf8cd.gif)
+![introducesubstitutevisualbasic](https://user-images.githubusercontent.com/7378346/77374922-564cf100-6d6c-11ea-8fca-96d8a9724b36.gif)

src/NSubstitute.Analyzers.CSharp/CodeRefactoringProviders/IntroduceSubstituteCodeRefactoringProvider.cs

@@ -0,0 +1,72 @@
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeRefactorings;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Text;
+using NSubstitute.Analyzers.Shared.CodeRefactoringProviders;
+using static Microsoft.CodeAnalysis.CSharp.SyntaxFactory;
+
+namespace NSubstitute.Analyzers.CSharp.CodeRefactoringProviders
+{
+    [ExportCodeRefactoringProvider(LanguageNames.CSharp)]
+    internal sealed class IntroduceSubstituteCodeRefactoringProvider : AbstractIntroduceSubstituteCodeRefactoringProvider<ObjectCreationExpressionSyntax, ArgumentListSyntax, ArgumentSyntax>
+    {
+        protected override IReadOnlyList<ArgumentSyntax> GetArgumentSyntaxNodes(ArgumentListSyntax argumentListSyntax, TextSpan span)
+        {
+            return argumentListSyntax.Arguments;
+        }
+
+        protected override ObjectCreationExpressionSyntax UpdateObjectCreationExpression(
+            ObjectCreationExpressionSyntax objectCreationExpressionSyntax,
+            IReadOnlyList<ArgumentSyntax> updatedArguments)
+        {
+            var originalArgumentList = objectCreationExpressionSyntax.ArgumentList;
+            var updatedArgumentList = originalArgumentList.Update(
+                originalArgumentList.OpenParenToken.WithTrailingTrivia(),
+                SeparatedList(updatedArguments),
+                originalArgumentList.CloseParenToken);
+
+            updatedArgumentList = UpdateArgumentListTrivia(originalArgumentList, updatedArgumentList);
+
+            return objectCreationExpressionSyntax.WithArgumentList(updatedArgumentList);
+        }
+
+        protected override SyntaxNode FindSiblingNodeForLocalSubstitute(ObjectCreationExpressionSyntax creationExpression)
+        {
+            var container = creationExpression.Ancestors()
+                .FirstOrDefault(ancestor => ancestor.Kind() == SyntaxKind.Block);
+
+            return container?.ChildNodes().FirstOrDefault();
+        }
+
+        protected override SyntaxNode FindSiblingNodeForReadonlySubstitute(SyntaxNode creationExpression)
+        {
+            var typeDeclarationSyntax = creationExpression.Ancestors()
+                .OfType<TypeDeclarationSyntax>()
+                .FirstOrDefault();
+
+            return typeDeclarationSyntax?.Members.FirstOrDefault();
+        }
+
+        private static ArgumentListSyntax UpdateArgumentListTrivia(
+            ArgumentListSyntax originalArgumentList,
+            ArgumentListSyntax updatedArgumentList)
+        {
+            if (originalArgumentList.CloseParenToken.IsMissing == false)
+            {
+                return updatedArgumentList;
+            }
+
+            var token = originalArgumentList.ChildTokens().LastOrDefault(innerToken => innerToken.IsMissing == false);
+
+            if (token.Kind() != SyntaxKind.None && token.HasTrailingTrivia)
+            {
+                updatedArgumentList = updatedArgumentList.WithTrailingTrivia(token.TrailingTrivia);
+            }
+
+            return updatedArgumentList;
+        }
+    }
+}

src/NSubstitute.Analyzers.Shared/CodeRefactoringProviders/AbstractIntroduceSubstituteCodeRefactoringProvider.cs

@@ -0,0 +1,286 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeRefactorings;
+using Microsoft.CodeAnalysis.Editing;
+using Microsoft.CodeAnalysis.Text;
+using NSubstitute.Analyzers.Shared.Extensions;
+
+namespace NSubstitute.Analyzers.Shared.CodeRefactoringProviders
+{
+    internal abstract class AbstractIntroduceSubstituteCodeRefactoringProvider<TObjectCreationExpressionSyntax, TArgumentListSyntax, TArgumentSyntax> : CodeRefactoringProvider
+        where TObjectCreationExpressionSyntax : SyntaxNode
+        where TArgumentListSyntax : SyntaxNode
+        where TArgumentSyntax : SyntaxNode
+    {
+        public sealed override async Task ComputeRefactoringsAsync(CodeRefactoringContext context)
+        {
+            var root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            var node = root.FindNode(context.Span);
+
+            if (!(node is TArgumentListSyntax argumentListSyntax) ||
+                !(node.Parent is TObjectCreationExpressionSyntax objectCreationExpressionSyntax))
+            {
+                return;
+            }
+
+            var semanticModel = await context.Document.GetSemanticModelAsync();
+            var refactoringActions = CreateRefactoringActions(
+                context,
+                semanticModel,
+                objectCreationExpressionSyntax,
+                argumentListSyntax);
+
+            foreach (var refactoringAction in refactoringActions)
+            {
+                context.RegisterRefactoring(refactoringAction);
+            }
+        }
+
+        protected abstract IReadOnlyList<TArgumentSyntax> GetArgumentSyntaxNodes(TArgumentListSyntax argumentListSyntax, TextSpan span);
+
+        protected abstract TObjectCreationExpressionSyntax UpdateObjectCreationExpression(
+            TObjectCreationExpressionSyntax objectCreationExpressionSyntax,
+            IReadOnlyList<TArgumentSyntax> argumentSyntax);
+
+        protected virtual bool IsMissing(TArgumentSyntax argumentSyntax) => argumentSyntax.IsMissing;
+
+        protected abstract SyntaxNode FindSiblingNodeForLocalSubstitute(TObjectCreationExpressionSyntax creationExpression);
+
+        protected abstract SyntaxNode FindSiblingNodeForReadonlySubstitute(SyntaxNode creationExpression);
+
+        private IEnumerable<CodeAction> CreateRefactoringActions(
+            CodeRefactoringContext context,
+            SemanticModel semanticModel,
+            TObjectCreationExpressionSyntax objectCreationExpressionSyntax,
+            TArgumentListSyntax argumentListSyntax)
+        {
+            var constructorSymbol = GetKnownConstructorSymbol(semanticModel, objectCreationExpressionSyntax);
+
+            if (constructorSymbol == null || constructorSymbol.Parameters.Length == 0)
+            {
+                yield break;
+            }
+
+            var existingArguments = GetArgumentSyntaxNodes(argumentListSyntax, context.Span);
+            var constructorParameters = constructorSymbol.Parameters.OrderBy(parameter => parameter.Ordinal).ToList();
+
+            var missingArgumentsPositions = GetMissingArgumentsPositions(existingArguments, constructorParameters);
+            if (missingArgumentsPositions.Count == 0)
+            {
+                yield break;
+            }
+
+            var localSubstituteSiblingNode = FindSiblingNodeForLocalSubstitute(objectCreationExpressionSyntax);
+            var readonlySubstituteSiblingNode = FindSiblingNodeForReadonlySubstitute(objectCreationExpressionSyntax);
+
+            var argumentIndexAtSpan = FindArgumentIndexAtSpan(existingArguments, context.Span);
+            if (missingArgumentsPositions.Contains(argumentIndexAtSpan))
+            {
+                var substituteName = constructorParameters[argumentIndexAtSpan].ToMinimalSymbolString(semanticModel);
+
+                if (localSubstituteSiblingNode != null)
+                {
+                    yield return CodeAction.Create(
+                        $"Introduce local substitute for {substituteName}",
+                        token => IntroduceLocalSubstitute(
+                            context,
+                            objectCreationExpressionSyntax,
+                            existingArguments,
+                            constructorParameters,
+                            new[] { argumentIndexAtSpan },
+                            localSubstituteSiblingNode));
+                }
+
+                if (readonlySubstituteSiblingNode != null)
+                {
+                    yield return CodeAction.Create(
+                        $"Introduce readonly substitute for {substituteName}",
+                        token => IntroduceReadonlySubstitute(
+                            context,
+                            objectCreationExpressionSyntax,
+                            existingArguments,
+                            constructorParameters,
+                            new[] { argumentIndexAtSpan },
+                            readonlySubstituteSiblingNode));
+                }
+            }
+
+            if (localSubstituteSiblingNode != null)
+            {
+                yield return CodeAction.Create(
+                    "Introduce local substitutes for missing arguments",
+                    token => IntroduceLocalSubstitute(
+                        context,
+                        objectCreationExpressionSyntax,
+                        existingArguments,
+                        constructorParameters,
+                        missingArgumentsPositions,
+                        localSubstituteSiblingNode));
+            }
+
+            if (readonlySubstituteSiblingNode != null)
+            {
+                yield return CodeAction.Create(
+                    "Introduce readonly substitutes for missing arguments",
+                    token => IntroduceReadonlySubstitute(
+                        context,
+                        objectCreationExpressionSyntax,
+                        existingArguments,
+                        constructorParameters,
+                        missingArgumentsPositions,
+                        readonlySubstituteSiblingNode));
+            }
+        }
+
+        private async Task<Document> IntroduceReadonlySubstitute(
+            CodeRefactoringContext context,
+            TObjectCreationExpressionSyntax objectCreationExpressionSyntax,
+            IReadOnlyList<TArgumentSyntax> existingArguments,
+            IReadOnlyList<IParameterSymbol> constructorParameters,
+            IReadOnlyList<int> missingArgumentsPositions,
+            SyntaxNode siblingNode)
+        {
+            SyntaxNode CreateFieldDeclaration(SyntaxGenerator syntaxGenerator, IParameterSymbol parameterSymbol, SyntaxNode invocationExpression)
+            {
+                return syntaxGenerator.FieldDeclaration(
+                    parameterSymbol.Name,
+                    syntaxGenerator.TypeExpression(parameterSymbol.Type),
+                    Accessibility.Private,
+                    DeclarationModifiers.ReadOnly,
+                    invocationExpression);
+            }
+
+            return await IntroduceSubstitute(
+                context,
+                objectCreationExpressionSyntax,
+                existingArguments,
+                constructorParameters,
+                missingArgumentsPositions,
+                siblingNode,
+                CreateFieldDeclaration);
+        }
+
+        private async Task<Document> IntroduceLocalSubstitute(
+            CodeRefactoringContext context,
+            TObjectCreationExpressionSyntax objectCreationExpressionSyntax,
+            IReadOnlyList<TArgumentSyntax> existingArguments,
+            IReadOnlyList<IParameterSymbol> constructorParameters,
+            IReadOnlyList<int> missingArgumentsPositions,
+            SyntaxNode siblingNode)
+        {
+            SyntaxNode CreateLocalDeclaration(SyntaxGenerator syntaxGenerator, IParameterSymbol parameterSymbol, SyntaxNode invocationExpression)
+            {
+                return syntaxGenerator.LocalDeclarationStatement(parameterSymbol.Name, invocationExpression);
+            }
+
+            return await IntroduceSubstitute(
+                context,
+                objectCreationExpressionSyntax,
+                existingArguments,
+                constructorParameters,
+                missingArgumentsPositions,
+                siblingNode,
+                CreateLocalDeclaration);
+        }
+
+        private async Task<Document> IntroduceSubstitute(
+            CodeRefactoringContext context,
+            TObjectCreationExpressionSyntax objectCreationExpressionSyntax,
+            IReadOnlyList<TArgumentSyntax> existingArguments,
+            IReadOnlyList<IParameterSymbol> constructorParameters,
+            IReadOnlyList<int> missingArgumentsPositions,
+            SyntaxNode siblingNode,
+            Func<SyntaxGenerator, IParameterSymbol, SyntaxNode, SyntaxNode> declarationFactory)
+        {
+            var documentEditor = await DocumentEditor.CreateAsync(context.Document);
+            var syntaxGenerator = documentEditor.Generator;
+            var declarations = new List<SyntaxNode>();
+            var newArgumentList = new List<TArgumentSyntax>();
+
+            for (var parameterPosition = 0; parameterPosition < constructorParameters.Count; parameterPosition++)
+            {
+                var parameterSymbol = constructorParameters[parameterPosition];
+                if (missingArgumentsPositions.Contains(parameterPosition))
+                {
+                    var invocationExpression = syntaxGenerator.SubstituteForInvocationExpression(parameterSymbol);
+
+                    var declaration = declarationFactory(
+                        syntaxGenerator,
+                        parameterSymbol,
+                        invocationExpression);
+
+                    declarations.Add(declaration);
+
+                    newArgumentList.Add((TArgumentSyntax)syntaxGenerator.Argument(syntaxGenerator.IdentifierName(parameterSymbol.Name)));
+                }
+                else if (parameterPosition < existingArguments.Count)
+                {
+                    newArgumentList.Add(existingArguments[parameterPosition]);
+                }
+            }
+
+            documentEditor.InsertBefore(siblingNode, declarations);
+
+            documentEditor.ReplaceNode(
+                objectCreationExpressionSyntax,
+                UpdateObjectCreationExpression(objectCreationExpressionSyntax, newArgumentList));
+
+            return documentEditor.GetChangedDocument();
+        }
+
+        private IMethodSymbol GetKnownConstructorSymbol(SemanticModel semanticModel, TObjectCreationExpressionSyntax objectCreationExpressionSyntax)
+        {
+            var symbol = semanticModel.GetSymbolInfo(objectCreationExpressionSyntax);
+
+            if (symbol.Symbol is IMethodSymbol methodSymbol)
+            {
+                return methodSymbol;
+            }
+
+            var candidateMethodSymbols = symbol.CandidateSymbols.OfType<IMethodSymbol>().ToList();
+
+            if (candidateMethodSymbols.Count == 0 || candidateMethodSymbols.Count > 1)
+            {
+                return null;
+            }
+
+            return candidateMethodSymbols.Single();
+        }
+
+        private IReadOnlyList<int> GetMissingArgumentsPositions(
+            IReadOnlyList<TArgumentSyntax> argumentSyntaxNodes,
+            IReadOnlyList<IParameterSymbol> parameterSymbols)
+        {
+            if (parameterSymbols.Count == 0)
+            {
+                return Array.Empty<int>();
+            }
+
+            if (argumentSyntaxNodes.Count == 0)
+            {
+                return Enumerable.Range(0, parameterSymbols.Count).ToList();
+            }
+
+            var result = new List<int>();
+            for (var symbolPosition = 0; symbolPosition < parameterSymbols.Count; symbolPosition++)
+            {
+                if (symbolPosition >= argumentSyntaxNodes.Count || IsMissing(argumentSyntaxNodes[symbolPosition]))
+                {
+                   result.Add(symbolPosition);
+                }
+            }
+
+            return result;
+        }
+
+        private int FindArgumentIndexAtSpan(IReadOnlyList<TArgumentSyntax> argumentSyntaxNodes, TextSpan span)
+        {
+            var findArgumentIndexAtSpan = argumentSyntaxNodes.IndexOf(node => node.FullSpan.IntersectsWith(span));
+            return findArgumentIndexAtSpan >= 0 ? findArgumentIndexAtSpan : 0;
+        }
+    }
+}

src/NSubstitute.Analyzers.Shared/Extensions/IEnumerableExtensions.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+
+namespace NSubstitute.Analyzers.Shared.Extensions
+{
+    internal static class IEnumerableExtensions
+    {
+        public static int IndexOf<T>(this IEnumerable<T> source, Func<T, bool> predicate)
+        {
+            var index = -1;
+            foreach (var item in source)
+            {
+                index++;
+                if (predicate(item))
+                {
+                    return index;
+                }
+            }
+
+            return index;
+        }
+    }
+}