File: CodeRefactorings\InlineTemporary\InlineTemporaryCodeRefactoringProvider.cs
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Project: src\src\Features\CSharp\Portable\Microsoft.CodeAnalysis.CSharp.Features.csproj (Microsoft.CodeAnalysis.CSharp.Features)
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
#nullable disable
 
using System;
using System.Collections.Immutable;
using System.Composition;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeRefactorings;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Formatting;
using Microsoft.CodeAnalysis.InlineTemporary;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Simplification;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.CSharp.CodeRefactorings.InlineTemporary;
 
[ExportCodeRefactoringProvider(LanguageNames.CSharp, Name = PredefinedCodeRefactoringProviderNames.InlineTemporary), Shared]
[method: ImportingConstructor]
[method: SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
internal sealed partial class CSharpInlineTemporaryCodeRefactoringProvider()
    : AbstractInlineTemporaryCodeRefactoringProvider<IdentifierNameSyntax, VariableDeclaratorSyntax>
{
    private static readonly SyntaxAnnotation DefinitionAnnotation = new();
    private static readonly SyntaxAnnotation ReferenceAnnotation = new();
    private static readonly SyntaxAnnotation ExpressionAnnotation = new();
 
    public override async Task ComputeRefactoringsAsync(CodeRefactoringContext context)
    {
        var (document, _, cancellationToken) = context;
        if (document.Project.Solution.WorkspaceKind == WorkspaceKind.MiscellaneousFiles)
        {
            return;
        }
 
        var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
 
        var variableDeclarator = await context.TryGetRelevantNodeAsync<VariableDeclaratorSyntax>().ConfigureAwait(false);
        if (variableDeclarator == null)
        {
            return;
        }
 
        if (variableDeclarator.Parent is not VariableDeclarationSyntax variableDeclaration ||
            variableDeclaration.Parent is not LocalDeclarationStatementSyntax localDeclarationStatement)
        {
            return;
        }
 
        if (variableDeclarator.Initializer == null ||
            variableDeclarator.Initializer.Value.IsMissing ||
            variableDeclarator.Initializer.Value.IsKind(SyntaxKind.StackAllocArrayCreationExpression))
        {
            return;
        }
 
        if (variableDeclaration.Type.Kind() == SyntaxKind.RefType)
        {
            // TODO: inlining ref returns:
            // https://github.com/dotnet/roslyn/issues/17132
            return;
        }
 
        if (localDeclarationStatement.ContainsDiagnostics ||
            localDeclarationStatement.UsingKeyword != default)
        {
            return;
        }
 
        var references = await GetReferenceLocationsAsync(document, variableDeclarator, cancellationToken).ConfigureAwait(false);
        if (!references.Any())
            return;
 
        // If the variable is itself referenced in its own initializer then don't offer anything here.  This
        // practically does not occur (though the language allows it), and it only serves to add a huge amount
        // of complexity to this feature.
        if (references.Any(static (r, variableDeclarator) => variableDeclarator.Initializer.Span.Contains(r.Span), variableDeclarator))
            return;
 
        context.RegisterRefactoring(
            CodeAction.Create(
                FeaturesResources.Inline_temporary_variable,
                cancellationToken => InlineTemporaryAsync(document, variableDeclarator, cancellationToken),
                nameof(FeaturesResources.Inline_temporary_variable)),
            variableDeclarator.Span);
    }
 
    private static bool HasConflict(IdentifierNameSyntax identifier, VariableDeclaratorSyntax variableDeclarator)
    {
        // TODO: Check for more conflict types.
        if (identifier.SpanStart < variableDeclarator.SpanStart)
            return true;
 
        var identifierNode = identifier.WalkUpParentheses();
        if (IsInDeconstructionAssignmentLeft(identifierNode))
            return true;
 
        if (identifierNode?.Parent is ArgumentSyntax argument)
        {
            if (argument.RefOrOutKeyword.Kind() != SyntaxKind.None)
                return true;
        }
        else if (identifierNode.Parent.Kind() is
            SyntaxKind.PreDecrementExpression or
            SyntaxKind.PreIncrementExpression or
            SyntaxKind.PostDecrementExpression or
            SyntaxKind.PostIncrementExpression or
            SyntaxKind.AddressOfExpression)
        {
            return true;
        }
        else if (identifierNode.Parent is AssignmentExpressionSyntax binaryExpression &&
                 binaryExpression.Left == identifierNode)
        {
            return true;
        }
 
        return false;
    }
 
    private static SyntaxAnnotation CreateConflictAnnotation()
        => ConflictAnnotation.Create(CSharpFeaturesResources.Conflict_s_detected);
 
    private static async Task<Document> InlineTemporaryAsync(Document document, VariableDeclaratorSyntax declarator, CancellationToken cancellationToken)
    {
        // Create the expression that we're actually going to inline.
        var expressionToInline = await CreateExpressionToInlineAsync(document, declarator, cancellationToken).ConfigureAwait(false);
        expressionToInline = expressionToInline.WithoutTrivia().Parenthesize().WithAdditionalAnnotations(Simplifier.Annotation, ExpressionAnnotation);
 
        // Annotate the variable declarator so that we can get back to it later.
        document = await document.ReplaceNodeAsync(declarator, declarator.WithAdditionalAnnotations(DefinitionAnnotation), cancellationToken).ConfigureAwait(false);
 
        declarator = await FindDeclaratorAsync(document, cancellationToken).ConfigureAwait(false);
 
        // Collect the identifier names for each reference.
        var allReferences = await GetReferenceLocationsAsync(document, declarator, cancellationToken).ConfigureAwait(false);
 
        // Add referenceAnnotations to identifier nodes being replaced.
        document = await document.ReplaceNodesAsync(
            allReferences,
            (o, n) => n.WithAdditionalAnnotations(ReferenceAnnotation),
            cancellationToken).ConfigureAwait(false);
 
        declarator = await FindDeclaratorAsync(document, cancellationToken).ConfigureAwait(false);
 
        allReferences = await FindReferenceAnnotatedNodesAsync(document, cancellationToken).ConfigureAwait(false);
 
        var conflictReferences = allReferences.Where(n => HasConflict(n, declarator)).ToSet();
        var nonConflictReferences = allReferences.Where(n => !conflictReferences.Contains(n)).ToSet();
 
        // Checks to see if inlining the temporary variable may change the code's meaning. This can only apply if the variable has two or more
        // references. We later use this heuristic to determine whether or not to display a warning message to the user.
        var mayContainSideEffects = allReferences.Count() > 1 &&
            MayContainSideEffects(declarator.Initializer.Value);
 
        var scope = GetScope(declarator);
        var newScope = ReferenceRewriter.Visit(scope, conflictReferences, nonConflictReferences, expressionToInline, cancellationToken);
 
        document = await document.ReplaceNodeAsync(scope, newScope, cancellationToken).ConfigureAwait(false);
 
        declarator = await FindDeclaratorAsync(document, cancellationToken).ConfigureAwait(false);
        newScope = GetScope(declarator);
 
        // Note that we only remove the local declaration if there weren't any conflicts,
        if (conflictReferences.Count == 0)
        {
            // No semantic conflicts, we can remove the definition.
            document = await document.ReplaceNodeAsync(
                newScope, RemoveDeclaratorFromScope(declarator, newScope), cancellationToken).ConfigureAwait(false);
        }
 
        // Finally, check all the places we inlined an expression and add some final warnings there if appropriate.
        var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
        var topmostParentingExpressions = root.GetAnnotatedNodes(ExpressionAnnotation)
            .OfType<ExpressionSyntax>()
            .Select(e => GetTopMostParentingExpression(e));
 
        var semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
 
        // Make each topmost parenting statement or Equals Clause Expressions semantically explicit.
        document = await document.ReplaceNodesAsync(topmostParentingExpressions, (original, current) =>
        {
            // warn when inlining into a conditional expression, as the inlined expression will not be executed.
            if (semanticModel.GetSymbolInfo(original, cancellationToken).Symbol is IMethodSymbol { IsConditional: true })
            {
                current = current.WithAdditionalAnnotations(
                    WarningAnnotation.Create(CSharpFeaturesResources.Warning_Inlining_temporary_into_conditional_method_call));
            }
 
            // If the refactoring may potentially change the code's semantics, display a warning message to the user.
            // on the first inlined location.
            if (mayContainSideEffects)
            {
                current = current.WithAdditionalAnnotations(
                    WarningAnnotation.Create(CSharpFeaturesResources.Warning_Inlining_temporary_variable_may_change_code_meaning));
                mayContainSideEffects = false;
            }
 
            return current;
        }, cancellationToken).ConfigureAwait(false);
 
        return document;
    }
 
    private static bool MayContainSideEffects(SyntaxNode expression)
    {
        // Checks to see if inlining the temporary variable may change the code's semantics. 
        // This is not meant to be an exhaustive check; it's more like a heuristic for obvious cases we know may cause side effects.
 
        var descendantNodesAndSelf = expression.DescendantNodesAndSelf();
 
        // Object creation:
        // e.g.:
        //     var [||]c = new C();
        //     c.P = 1;
        //     var x = c;
        // After refactoring:
        //     new C().P = 1;
        //     var x = new C();
 
        // Invocation:
        // e.g. - let method M return a new instance of an object containing property P:
        //     var [||]c = M();
        //     c.P = 0;
        //     var x = c;
        // After refactoring:
        //     M().P = 0;
        //     var x = M();
        if (descendantNodesAndSelf.Any(n => n.Kind() is SyntaxKind.ObjectCreationExpression or SyntaxKind.InvocationExpression))
        {
            return true;
        }
 
        // Assume if we reach here that the refactoring won't cause side effects.
        return false;
    }
 
    private static async Task<VariableDeclaratorSyntax> FindDeclaratorAsync(Document document, CancellationToken cancellationToken)
        => await FindNodeWithAnnotationAsync<VariableDeclaratorSyntax>(document, DefinitionAnnotation, cancellationToken).ConfigureAwait(false);
 
    private static async Task<T> FindNodeWithAnnotationAsync<T>(Document document, SyntaxAnnotation annotation, CancellationToken cancellationToken)
        where T : SyntaxNode
    {
        var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
        return root
            .GetAnnotatedNodesAndTokens(annotation)
            .Single()
            .AsNode() as T;
    }
 
    private static async Task<ImmutableArray<IdentifierNameSyntax>> FindReferenceAnnotatedNodesAsync(Document document, CancellationToken cancellationToken)
    {
        var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
        return root.GetAnnotatedNodesAndTokens(ReferenceAnnotation).Select(n => (IdentifierNameSyntax)n.AsNode()).ToImmutableArray();
    }
 
    private static SyntaxNode GetScope(VariableDeclaratorSyntax variableDeclarator)
    {
        var variableDeclaration = (VariableDeclarationSyntax)variableDeclarator.Parent;
        var localDeclaration = (LocalDeclarationStatementSyntax)variableDeclaration.Parent;
        var scope = localDeclaration.Parent;
 
        while (scope.IsKind(SyntaxKind.LabeledStatement))
            scope = scope.Parent;
 
        var parentExpressions = scope.AncestorsAndSelf().OfType<ExpressionSyntax>();
        scope = parentExpressions.LastOrDefault()?.Parent ?? scope;
 
        if (scope.IsKind(SyntaxKind.GlobalStatement))
            scope = scope.Parent;
 
        return scope;
    }
 
    private static VariableDeclaratorSyntax FindDeclarator(SyntaxNode node)
    {
        var annotatedNodesOrTokens = node.GetAnnotatedNodesAndTokens(DefinitionAnnotation).ToList();
        Debug.Assert(annotatedNodesOrTokens.Count == 1, "Only a single variable declarator should have been annotated.");
 
        return (VariableDeclaratorSyntax)annotatedNodesOrTokens.First().AsNode();
    }
 
    private static SyntaxNode RemoveDeclaratorFromVariableList(VariableDeclaratorSyntax variableDeclarator, VariableDeclarationSyntax variableDeclaration)
    {
        Debug.Assert(variableDeclaration.Variables.Count > 1);
        Debug.Assert(variableDeclaration.Variables.Contains(variableDeclarator));
 
        var localDeclaration = (LocalDeclarationStatementSyntax)variableDeclaration.Parent;
        var scope = GetScope(variableDeclarator);
 
        var newLocalDeclaration = variableDeclarator.GetLeadingTrivia().Any(t => t.IsDirective)
            ? localDeclaration.RemoveNode(variableDeclarator, SyntaxRemoveOptions.KeepExteriorTrivia)
            : localDeclaration.RemoveNode(variableDeclarator, SyntaxRemoveOptions.KeepNoTrivia);
 
        return scope.ReplaceNode(
            localDeclaration,
            newLocalDeclaration.WithAdditionalAnnotations(Formatter.Annotation));
    }
 
    private static SyntaxNode RemoveDeclaratorFromScope(VariableDeclaratorSyntax variableDeclarator, SyntaxNode scope)
    {
        var variableDeclaration = (VariableDeclarationSyntax)variableDeclarator.Parent;
 
        // If there is more than one variable declarator, remove this one from the variable declaration.
        if (variableDeclaration.Variables.Count > 1)
            return RemoveDeclaratorFromVariableList(variableDeclarator, variableDeclaration);
 
        var localDeclaration = (LocalDeclarationStatementSyntax)variableDeclaration.Parent;
 
        // There's only one variable declarator, so we'll remove the local declaration
        // statement entirely. This means that we'll concatenate the leading and trailing
        // trivia of this declaration and move it to the next statement.
        var leadingTrivia = localDeclaration
            .GetLeadingTrivia()
            .Reverse()
            .SkipWhile(t => t.IsKind(SyntaxKind.WhitespaceTrivia))
            .Reverse()
            .ToSyntaxTriviaList();
 
        var trailingTrivia = localDeclaration
            .GetTrailingTrivia()
            .SkipWhile(t => t is (kind: SyntaxKind.WhitespaceTrivia or SyntaxKind.EndOfLineTrivia))
            .ToSyntaxTriviaList();
 
        var newLeadingTrivia = leadingTrivia.Concat(trailingTrivia);
 
        var nextToken = localDeclaration.GetLastToken().GetNextTokenOrEndOfFile();
        var newNextToken = nextToken.WithPrependedLeadingTrivia(newLeadingTrivia)
                                    .WithAdditionalAnnotations(Formatter.Annotation);
 
        var newScope = scope.ReplaceToken(nextToken, newNextToken);
 
        var newLocalDeclaration = (LocalDeclarationStatementSyntax)FindDeclarator(newScope).Parent.Parent;
 
        // If the local is parented by a label statement, we can't remove this statement. Instead,
        // we'll replace the local declaration with an empty expression statement.
        if (newLocalDeclaration?.Parent is LabeledStatementSyntax labeledStatement)
        {
            var newLabeledStatement = labeledStatement.ReplaceNode(newLocalDeclaration, SyntaxFactory.ParseStatement(""));
            return newScope.ReplaceNode(labeledStatement, newLabeledStatement);
        }
 
        // If the local is parented by a global statement, we need to remove the parent global statement.
        if (newLocalDeclaration?.Parent is GlobalStatementSyntax globalStatement)
        {
            return newScope.RemoveNode(globalStatement, SyntaxRemoveOptions.KeepNoTrivia);
        }
 
        return newScope.RemoveNode(newLocalDeclaration, SyntaxRemoveOptions.KeepNoTrivia);
    }
 
    private static async Task<ExpressionSyntax> CreateExpressionToInlineAsync(
        Document document,
        VariableDeclaratorSyntax variableDeclarator,
        CancellationToken cancellationToken)
    {
        var text = await document.GetValueTextAsync(cancellationToken).ConfigureAwait(false);
        var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
        var expression = variableDeclarator.Initializer.Value.WalkDownParentheses();
 
        var expressionToInline = CreateExpressionToInline();
 
        // If we are moving something multiline to a new location, add the formatter annotation to it so we can
        // attempt to ensure it gets properly indented/dedented there.
        if (!text.AreOnSameLine(expression.SpanStart, expression.Span.End))
            expressionToInline = expressionToInline.WithAdditionalAnnotations(Formatter.Annotation);
 
        return expressionToInline;
 
        ExpressionSyntax CreateExpressionToInline()
        {
            var isVar = ((VariableDeclarationSyntax)variableDeclarator.Parent).Type.IsVar;
            var localSymbol = (ILocalSymbol)semanticModel.GetDeclaredSymbol(variableDeclarator, cancellationToken);
 
            if (expression is ImplicitObjectCreationExpressionSyntax implicitCreation)
            {
                // Consider: C c = new(); Console.WriteLine(c.ToString());
                // Inlining result should be: Console.WriteLine(new C().ToString()); instead of Console.WriteLine(new().ToString());
                // This condition converts implicit object creation expression to normal object creation expression.
 
                var type = localSymbol.Type.GenerateTypeSyntax();
                return SyntaxFactory.ObjectCreationExpression(implicitCreation.NewKeyword, type, implicitCreation.ArgumentList, implicitCreation.Initializer);
            }
            else if (expression is InitializerExpressionSyntax(SyntaxKind.ArrayInitializerExpression) arrayInitializer)
            {
                // If this is an array initializer, we need to transform it into an array creation
                // expression for inlining.
 
                var arrayType = (ArrayTypeSyntax)localSymbol.Type.GenerateTypeSyntax();
 
                // Add any non-whitespace trailing trivia from the equals clause to the type.
                var equalsToken = variableDeclarator.Initializer.EqualsToken;
                if (equalsToken.HasTrailingTrivia)
                {
                    var trailingTrivia = equalsToken.TrailingTrivia.SkipInitialWhitespace();
                    if (trailingTrivia.Any())
                        arrayType = arrayType.WithTrailingTrivia(trailingTrivia);
                }
 
                return SyntaxFactory.ArrayCreationExpression(arrayType, arrayInitializer);
            }
            else if (isVar && expression is ObjectCreationExpressionSyntax or ArrayCreationExpressionSyntax or CastExpressionSyntax)
            {
                // if we have `var x = new Y();` there's no need to do any casting as the type is indicated
                // directly in the existing code.  The same holds for `new Y[]` or `(Y)...`
                return expression;
            }
            else
            {
                if (localSymbol.Type.ContainsAnonymousType() || localSymbol.Type is IErrorTypeSymbol { Name: null or "" })
                    return expression;
 
                return expression.Cast(localSymbol.Type);
            }
        }
    }
 
    private static SyntaxNode GetTopMostParentingExpression(ExpressionSyntax expression)
        => expression.AncestorsAndSelf().OfType<ExpressionSyntax>().Last();
 
    private static bool IsInDeconstructionAssignmentLeft(ExpressionSyntax node)
    {
        var parent = node.Parent;
        while (parent.Kind() is SyntaxKind.ParenthesizedExpression or SyntaxKind.CastExpression)
            parent = parent.Parent;
 
        while (parent.IsKind(SyntaxKind.Argument))
        {
            parent = parent.Parent;
            if (!parent.IsKind(SyntaxKind.TupleExpression))
            {
                return false;
            }
            else if (parent?.Parent is AssignmentExpressionSyntax(SyntaxKind.SimpleAssignmentExpression) assignment)
            {
                return assignment.Left == parent;
            }
 
            parent = parent.Parent;
        }
 
        return false;
    }
}