ILSpy/ICSharpCode.Decompiler/CSharp/Transforms/IntroduceExtensionMethods.cs

// Copyright (c) 2011 AlphaSierraPapa for the SharpDevelop Team
// 
// 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
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// 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
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using System;
using System.Collections.Generic;
using System.Linq;
using ICSharpCode.Decompiler.CSharp.Resolver;
using ICSharpCode.Decompiler.CSharp.Syntax;
using ICSharpCode.Decompiler.CSharp.TypeSystem;
using ICSharpCode.Decompiler.Semantics;
using ICSharpCode.Decompiler.TypeSystem;
using ICSharpCode.Decompiler.Util;

namespace ICSharpCode.Decompiler.CSharp.Transforms
{
	/// <summary>
	/// Converts extension method calls into infix syntax.
	/// </summary>
	public class IntroduceExtensionMethods : DepthFirstAstVisitor, IAstTransform
	{
		TransformContext context;
		CSharpResolver resolver;
		CSharpConversions conversions;

		public void Run(AstNode rootNode, TransformContext context)
		{
			this.context = context;
			this.conversions = CSharpConversions.Get(context.TypeSystem.Compilation);
			InitializeContext(rootNode.Annotation<UsingScope>());
			rootNode.AcceptVisitor(this);
		}

		Stack<CSharpTypeResolveContext> resolveContextStack = new Stack<CSharpTypeResolveContext>();

		void InitializeContext(UsingScope usingScope)
		{
			this.resolveContextStack = new Stack<CSharpTypeResolveContext>();
			if (!string.IsNullOrEmpty(context.DecompiledTypeDefinition?.Namespace)) {
				foreach (string ns in context.DecompiledTypeDefinition.Namespace.Split('.')) {
					usingScope = new UsingScope(usingScope, ns);
				}
			}
			var currentContext = new CSharpTypeResolveContext(context.TypeSystem.MainAssembly, usingScope.Resolve(context.TypeSystem.Compilation), context.DecompiledTypeDefinition);
			this.resolveContextStack.Push(currentContext);
			this.resolver = new CSharpResolver(currentContext);
		}

		public override void VisitNamespaceDeclaration(NamespaceDeclaration namespaceDeclaration)
		{
			var previousContext = resolveContextStack.Peek();
			var usingScope = previousContext.CurrentUsingScope.UnresolvedUsingScope;
			foreach (string ident in namespaceDeclaration.Identifiers) {
				usingScope = new UsingScope(usingScope, ident);
			}
			var currentContext = new CSharpTypeResolveContext(previousContext.CurrentAssembly, usingScope.Resolve(previousContext.Compilation));
			resolveContextStack.Push(currentContext);
			try {
				this.resolver = new CSharpResolver(currentContext);
				base.VisitNamespaceDeclaration(namespaceDeclaration);
			} finally {
				this.resolver = new CSharpResolver(previousContext);
				resolveContextStack.Pop();
			}
		}

		public override void VisitTypeDeclaration(TypeDeclaration typeDeclaration)
		{
			var previousContext = resolveContextStack.Peek();
			var currentContext = previousContext.WithCurrentTypeDefinition(typeDeclaration.GetSymbol() as ITypeDefinition);
			resolveContextStack.Push(currentContext);
			try {
				this.resolver = new CSharpResolver(currentContext);
				base.VisitTypeDeclaration(typeDeclaration);
			} finally {
				this.resolver = new CSharpResolver(previousContext);
				resolveContextStack.Pop();
			}
		}

		public override void VisitInvocationExpression(InvocationExpression invocationExpression)
		{
			base.VisitInvocationExpression(invocationExpression);
			var method = invocationExpression.GetSymbol() as IMethod;
			if (method == null || !method.IsExtensionMethod || !invocationExpression.Arguments.Any())
				return;
			IReadOnlyList<IType> typeArguments;
			MemberReferenceExpression memberRefExpr;
			switch (invocationExpression.Target) {
				case MemberReferenceExpression mre:
					typeArguments = mre.TypeArguments.Any() ? method.TypeArguments : EmptyList<IType>.Instance;
					memberRefExpr = mre;
					break;
				case IdentifierExpression ide:
					typeArguments = ide.TypeArguments.Any() ? method.TypeArguments : EmptyList<IType>.Instance;
					memberRefExpr = null;
					break;
				default: return;
			}
			
			var firstArgument = invocationExpression.Arguments.First();
			if (firstArgument is NamedArgumentExpression)
				return;
			var target = firstArgument.GetResolveResult();
			if (target is ConstantResolveResult crr && crr.ConstantValue == null) {
				target = new ConversionResolveResult(method.Parameters[0].Type, crr, Conversion.NullLiteralConversion);
			}
			ResolveResult[] args = new ResolveResult[invocationExpression.Arguments.Count - 1];
			string[] argNames = null;
			int pos = 0;
			foreach (var arg in invocationExpression.Arguments.Skip(1)) {
				if (arg is NamedArgumentExpression nae) {
					if (argNames == null) {
						argNames = new string[args.Length];
					}
					argNames[pos] = nae.Name;
					args[pos] = nae.Expression.GetResolveResult();
				} else {
					args[pos] = arg.GetResolveResult();
				}
				pos++;
			}
			if (!CanTransformToExtensionMethodCall(resolver, method, typeArguments, target, args, argNames))
				return;
			if (firstArgument is NullReferenceExpression)
				firstArgument = firstArgument.ReplaceWith(expr => new CastExpression(context.TypeSystemAstBuilder.ConvertType(method.Parameters[0].Type), expr.Detach()));
			if (invocationExpression.Target is IdentifierExpression identifierExpression) {
				identifierExpression.Detach();
				memberRefExpr = new MemberReferenceExpression(firstArgument.Detach(), method.Name, identifierExpression.TypeArguments.Detach());
				invocationExpression.Target = memberRefExpr;
			} else {
				memberRefExpr.Target = firstArgument.Detach();
			}
		}

		public static bool CanTransformToExtensionMethodCall(CSharpResolver resolver, IMethod method,
			IReadOnlyList<IType> typeArguments, ResolveResult target, ResolveResult[] arguments, string[] argumentNames)
		{
			var rr = resolver.ResolveMemberAccess(target, method.Name, typeArguments, NameLookupMode.InvocationTarget) as MethodGroupResolveResult;
			if (rr == null)
				return false;
			var or = rr.PerformOverloadResolution(resolver.CurrentTypeResolveContext.Compilation, arguments, argumentNames, allowExtensionMethods: true);
			if (or == null || or.IsAmbiguous)
				return false;
			return method.Equals(or.GetBestCandidateWithSubstitutedTypeArguments());
		}
	}
}