/// <summary>
        /// Creates a speculative AttributeSemanticModel that allows asking semantic questions about an attribute node that did not appear in the original source code.
        /// </summary>
        public static AttributeSemanticModel CreateSpeculative(SyntaxTreeSemanticModel parentSemanticModel, AttributeSyntax syntax, NamedTypeSymbol attributeType, AliasSymbol aliasOpt, Binder rootBinder, int position)
        {
            Debug.Assert(parentSemanticModel != null);
            Debug.Assert(rootBinder != null);
            Debug.Assert(rootBinder.IsSemanticModelBinder);

            return new AttributeSemanticModel(parentSemanticModel.Compilation, syntax, attributeType, aliasOpt, rootBinder, parentSemanticModel, position);
        }

        protected BoundLocalDeclaration BindVariableDeclaration(
            LocalDeclarationKind kind,
            bool isVar,
            VariableDeclaratorSyntax declarator,
            TypeSyntax typeSyntax,
            TypeSymbol declTypeOpt,
            AliasSymbol aliasOpt,
            DiagnosticBag diagnostics,
            CSharpSyntaxNode associatedSyntaxNode = null)
        {
            Debug.Assert(declarator != null);

            return BindVariableDeclaration(LocateDeclaredVariableSymbol(declarator, typeSyntax),
                                           kind,
                                           isVar,
                                           declarator,
                                           typeSyntax,
                                           declTypeOpt,
                                           aliasOpt,
                                           diagnostics,
                                           associatedSyntaxNode);
        }

        private TypeSymbol BindVariableType(CSharpSyntaxNode declarationNode, DiagnosticBag diagnostics, TypeSyntax typeSyntax, ref bool isConst, out bool isVar, out AliasSymbol alias)
        {
            Debug.Assert(declarationNode.Kind() == SyntaxKind.LocalDeclarationStatement);

            // If the type is "var" then suppress errors when binding it. "var" might be a legal type
            // or it might not; if it is not then we do not want to report an error. If it is, then
            // we want to treat the declaration as an explicitly typed declaration.

            TypeSymbol declType = BindType(typeSyntax, diagnostics, out isVar, out alias);
            Debug.Assert((object)declType != null || isVar);

            if (isVar)
            {
                // There are a number of ways in which a var decl can be illegal, but in these 
                // cases we should report an error and then keep right on going with the inference.

                if (isConst)
                {
                    Error(diagnostics, ErrorCode.ERR_ImplicitlyTypedVariableCannotBeConst, declarationNode);
                    // Keep processing it as a non-const local.
                    isConst = false;
                }

                // In the dev10 compiler the error recovery semantics for the illegal case
                // "var x = 10, y = 123.4;" are somewhat undesirable.
                //
                // First off, this is an error because a straw poll of language designers and
                // users showed that there was no consensus on whether the above should mean
                // "double x = 10, y = 123.4;", taking the best type available and substituting
                // that for "var", or treating it as "var x = 10; var y = 123.4;" -- since there
                // was no consensus we decided to simply make it illegal. 
                //
                // In dev10 for error recovery in the IDE we do an odd thing -- we simply take
                // the type of the first variable and use it. So that is "int x = 10, y = 123.4;".
                // 
                // This seems less than ideal. In the error recovery scenario it probably makes
                // more sense to treat that as "var x = 10; var y = 123.4;" and do each inference
                // separately.

                if (declarationNode.Kind() == SyntaxKind.LocalDeclarationStatement && ((LocalDeclarationStatementSyntax)declarationNode).Declaration.Variables.Count > 1 && !declarationNode.HasErrors)
                {
                    Error(diagnostics, ErrorCode.ERR_ImplicitlyTypedVariableMultipleDeclarator, declarationNode);
                }
            }
            else
            {
                // In the native compiler when given a situation like
                //
                // D[] x;
                // 
                // where D is a static type we report both that D cannot be an element type
                // of an array, and that D[] is not a valid type for a local variable.
                // This seems silly; the first error is entirely sufficient. We no longer
                // produce additional errors for local variables of arrays of static types.

                if (declType.IsStatic)
                {
                    Error(diagnostics, ErrorCode.ERR_VarDeclIsStaticClass, typeSyntax, declType);
                }

                if (isConst && !declType.CanBeConst())
                {
                    Error(diagnostics, ErrorCode.ERR_BadConstType, typeSyntax, declType);
                    // Keep processing it as a non-const local.
                    isConst = false;
                }
            }

            return declType;
        }

        private static Imports BuildImports(CSharpCompilation compilation, PEModuleSymbol module, ImmutableArray<ImportRecord> importRecords, InContainerBinder binder)
        {
            // We make a first pass to extract all of the extern aliases because other imports may depend on them.
            var externsBuilder = ArrayBuilder<AliasAndExternAliasDirective>.GetInstance();
            foreach (var importRecord in importRecords)
            {
                if (importRecord.TargetKind != ImportTargetKind.Assembly)
                {
                    continue;
                }

                var alias = importRecord.Alias;
                IdentifierNameSyntax aliasNameSyntax;
                if (!TryParseIdentifierNameSyntax(alias, out aliasNameSyntax))
                {
                    Debug.WriteLine($"Import record '{importRecord}' has syntactically invalid extern alias '{alias}'");
                    continue;
                }

                var externAliasSyntax = SyntaxFactory.ExternAliasDirective(aliasNameSyntax.Identifier);
                var aliasSymbol = new AliasSymbol(binder, externAliasSyntax); // Binder is only used to access compilation.
                externsBuilder.Add(new AliasAndExternAliasDirective(aliasSymbol, externAliasDirective: null)); // We have one, but we pass null for consistency.
            }

            var externs = externsBuilder.ToImmutableAndFree();

            if (externs.Any())
            {
                // NB: This binder (and corresponding Imports) is only used to bind the other imports.
                // We'll merge the externs into a final Imports object and return that to be used in
                // the actual binder chain.
                binder = new InContainerBinder(
                    binder.Container,
                    binder,
                    Imports.FromCustomDebugInfo(binder.Compilation, ImmutableDictionary<string, AliasAndUsingDirective>.Empty, ImmutableArray<NamespaceOrTypeAndUsingDirective>.Empty, externs));
            }

            var usingAliases = ImmutableDictionary.CreateBuilder<string, AliasAndUsingDirective>();
            var usingsBuilder = ArrayBuilder<NamespaceOrTypeAndUsingDirective>.GetInstance();

            foreach (var importRecord in importRecords)
            {
                switch (importRecord.TargetKind)
                {
                    case ImportTargetKind.Type:
                        {
                            TypeSymbol typeSymbol = (TypeSymbol)importRecord.TargetType;
                            Debug.Assert((object)typeSymbol != null);

                            if (typeSymbol.IsErrorType())
                            {
                                // Type is unrecognized. The import may have been
                                // valid in the original source but unnecessary.
                                continue; // Don't add anything for this import.
                            }
                            else if (importRecord.Alias == null && !typeSymbol.IsStatic)
                            {
                                // Only static types can be directly imported.
                                continue;
                            }

                            if (!TryAddImport(importRecord.Alias, typeSymbol, usingsBuilder, usingAliases, binder, importRecord))
                            {
                                continue;
                            }

                            break;
                        }
                    case ImportTargetKind.Namespace:
                        {
                            var namespaceName = importRecord.TargetString;
                            NameSyntax targetSyntax;
                            if (!SyntaxHelpers.TryParseDottedName(namespaceName, out targetSyntax))
                            {
                                // DevDiv #999086: Some previous version of VS apparently generated type aliases as "UA{alias} T{alias-qualified type name}". 
                                // Neither Roslyn nor Dev12 parses such imports.  However, Roslyn discards them, rather than interpreting them as "UA{alias}"
                                // (which will rarely work and never be correct).
                                Debug.WriteLine($"Import record '{importRecord}' has syntactically invalid target '{importRecord.TargetString}'");
                                continue;
                            }

                            NamespaceSymbol globalNamespace;
                            AssemblySymbol targetAssembly = (AssemblySymbol)importRecord.TargetAssembly;

                            if (targetAssembly != null)
                            {
                                if (targetAssembly.IsMissing)
                                {
                                    Debug.WriteLine($"Import record '{importRecord}' has invalid assembly reference '{targetAssembly.Identity}'");
                                    continue;
                                }

                                globalNamespace = targetAssembly.GlobalNamespace;
                            }
                            else if (importRecord.TargetAssemblyAlias != null)
                            {
                                IdentifierNameSyntax externAliasSyntax = null;
                                if (!TryParseIdentifierNameSyntax(importRecord.TargetAssemblyAlias, out externAliasSyntax))
                                {
                                    Debug.WriteLine($"Import record '{importRecord}' has syntactically invalid extern alias '{importRecord.TargetAssemblyAlias}'");
//.........这里部分代码省略.........

 public BoundTypeExpression(CSharpSyntaxNode syntax, AliasSymbol aliasOpt, bool inferredType, TypeSymbol type, bool hasErrors = false)
     : this(syntax, aliasOpt, inferredType, null, type, hasErrors)
 {
 }

 private AttributeSemanticModel(CSharpCompilation compilation, AttributeSyntax syntax, NamedTypeSymbol attributeType, AliasSymbol aliasOpt, Binder rootBinder, SyntaxTreeSemanticModel parentSemanticModelOpt = null, int speculatedPosition = 0)
     : base(compilation, syntax, attributeType, rootBinder, parentSemanticModelOpt, speculatedPosition)
 {
     Debug.Assert(syntax != null);
     this.aliasOpt = aliasOpt;
 }

 /// <summary>
 /// Creates an AttributeSemanticModel that allows asking semantic questions about an attribute node.
 /// </summary>
 public static AttributeSemanticModel Create(CSharpCompilation compilation, AttributeSyntax syntax, NamedTypeSymbol attributeType, AliasSymbol aliasOpt, Binder rootBinder)
 {
     return new AttributeSemanticModel(compilation, syntax, attributeType, aliasOpt, rootBinder);
 }

 public AliasAndExternAliasDirective(AliasSymbol alias, ExternAliasDirectiveSyntax externAliasDirective)
 {
     this.Alias = alias;
     this.ExternAliasDirective = externAliasDirective;
 }

        protected BoundLocalDeclaration BindVariableDeclaration(
            LocalDeclarationKind kind,
            bool isVar,
            VariableDeclaratorSyntax declarator,
            TypeSyntax typeSyntax,
            TypeSymbol declTypeOpt,
            AliasSymbol aliasOpt,
            DiagnosticBag diagnostics,
            CSharpSyntaxNode associatedSyntaxNode = null)
        {
            Debug.Assert(declarator != null);
            Debug.Assert((object)declTypeOpt != null || isVar);
            Debug.Assert(typeSyntax != null);

            // if we are not given desired syntax, we use declarator
            associatedSyntaxNode = associatedSyntaxNode ?? declarator;

            bool hasErrors = false;

            BoundExpression initializerOpt;

            SourceLocalSymbol localSymbol = this.LookupLocal(declarator.Identifier);

            // In error scenarios with misplaced code, it is possible we can't bind the local declaration.
            // This occurs through the semantic model.  In that case concoct a plausible result.
            if ((object)localSymbol == null)
            {
                localSymbol = SourceLocalSymbol.MakeLocal(
                    ContainingMemberOrLambda as MethodSymbol, this, typeSyntax,
                    declarator.Identifier, declarator.Initializer, LocalDeclarationKind.Variable);
            }

            // Check for variable declaration errors.
            hasErrors |= this.EnsureDeclarationInvariantMeaningInScope(localSymbol, diagnostics);

            EqualsValueClauseSyntax equalsValueClauseSyntax = declarator.Initializer;
            if (isVar)
            {
                aliasOpt = null;

                var binder = new ImplicitlyTypedLocalBinder(this, localSymbol);
                initializerOpt = binder.BindInferredVariableInitializer(diagnostics, equalsValueClauseSyntax, declarator);

                // If we got a good result then swap the inferred type for the "var" 
                if (initializerOpt != null && (object)initializerOpt.Type != null)
                {
                    declTypeOpt = initializerOpt.Type;

                    if (declTypeOpt.SpecialType == SpecialType.System_Void)
                    {
                        Error(diagnostics, ErrorCode.ERR_ImplicitlyTypedVariableAssignedBadValue, declarator, declTypeOpt);
                        declTypeOpt = CreateErrorType("var");
                        hasErrors = true;
                    }

                    if (!declTypeOpt.IsErrorType())
                    {
                        if (declTypeOpt.IsStatic)
                        {
                            Error(diagnostics, ErrorCode.ERR_VarDeclIsStaticClass, typeSyntax, initializerOpt.Type);
                            hasErrors = true;
                        }
                    }
                }
                else
                {
                    declTypeOpt = CreateErrorType("var");
                    hasErrors = true;
                }
            }
            else
            {
                if (ReferenceEquals(equalsValueClauseSyntax, null))
                {
                    initializerOpt = null;
                }
                else
                {
                    // Basically inlined BindVariableInitializer, but with conversion optional.
                    initializerOpt = BindPossibleArrayInitializer(equalsValueClauseSyntax.Value, declTypeOpt, diagnostics);
                    if (kind != LocalDeclarationKind.Fixed)
                    {
                        // If this is for a fixed statement, we'll do our own conversion since there are some special cases.
                        initializerOpt = GenerateConversionForAssignment(declTypeOpt, initializerOpt, diagnostics);
                    }
                }
            }

            Debug.Assert((object)declTypeOpt != null);

            if (kind == LocalDeclarationKind.Fixed)
            {
                // NOTE: this is an error, but it won't prevent further binding.
                if (isVar)
                {
                    if (!hasErrors)
                    {
                        Error(diagnostics, ErrorCode.ERR_ImplicitlyTypedLocalCannotBeFixed, declarator);
                        hasErrors = true;
                    }
//.........这里部分代码省略.........

        private static Imports BuildImports(CSharpCompilation compilation, ImmutableArray<string> importStrings, InContainerBinder binder, MetadataDecoder metadataDecoder)
        {
            // We make a first pass to extract all of the extern aliases because other imports may depend on them.
            var externsBuilder = ArrayBuilder<AliasAndExternAliasDirective>.GetInstance();
            foreach (var importString in importStrings)
            {
                string alias;
                string externAlias;
                string target;
                ImportTargetKind kind;
                if (!CustomDebugInfoReader.TryParseCSharpImportString(importString, out alias, out externAlias, out target, out kind))
                {
                    Debug.WriteLine("Unable to parse import string '{0}'", (object)importString);
                    continue;
                }
                else if (kind != ImportTargetKind.Assembly)
                {
                    continue;
                }

                Debug.Assert(alias == null);
                Debug.Assert(externAlias != null);
                Debug.Assert(target == null);

                NameSyntax aliasNameSyntax;
                if (!SyntaxHelpers.TryParseDottedName(externAlias, out aliasNameSyntax) || aliasNameSyntax.Kind() != SyntaxKind.IdentifierName)
                {
                    Debug.WriteLine("Import string '{0}' has syntactically invalid extern alias '{1}'", importString, externAlias);
                    continue;
                }

                var aliasToken = ((IdentifierNameSyntax)aliasNameSyntax).Identifier;
                var externAliasSyntax = SyntaxFactory.ExternAliasDirective(aliasToken);
                var aliasSymbol = new AliasSymbol(binder, externAliasSyntax); // Binder is only used to access compilation.
                externsBuilder.Add(new AliasAndExternAliasDirective(aliasSymbol, externAliasSyntax));
            }

            var externs = externsBuilder.ToImmutableAndFree();

            if (externs.Any())
            {
                // NB: This binder (and corresponding Imports) is only used to bind the other imports.
                // We'll merge the externs into a final Imports object and return that to be used in
                // the actual binder chain.
                binder = new InContainerBinder(
                    binder.Container,
                    binder,
                    Imports.FromCustomDebugInfo(binder.Compilation, new Dictionary<string, AliasAndUsingDirective>(), ImmutableArray<NamespaceOrTypeAndUsingDirective>.Empty, externs));
            }

            var usingAliases = new Dictionary<string, AliasAndUsingDirective>();
            var usingsBuilder = ArrayBuilder<NamespaceOrTypeAndUsingDirective>.GetInstance();

            foreach (var importString in importStrings)
            {
                string alias;
                string externAlias;
                string target;
                ImportTargetKind kind;
                if (!CustomDebugInfoReader.TryParseCSharpImportString(importString, out alias, out externAlias, out target, out kind))
                {
                    Debug.WriteLine("Unable to parse import string '{0}'", (object)importString);
                    continue;
                }

                switch (kind)
                {
                    case ImportTargetKind.Type:
                        {
                            Debug.Assert(target != null, string.Format("Type import string '{0}' has no target", importString));
                            Debug.Assert(externAlias == null, string.Format("Type import string '{0}' has an extern alias (should be folded into target)", importString));

                            TypeSymbol typeSymbol = metadataDecoder.GetTypeSymbolForSerializedType(target);
                            Debug.Assert((object)typeSymbol != null);
                            if (typeSymbol.IsErrorType())
                            {
                                // Type is unrecognized. The import may have been
                                // valid in the original source but unnecessary.
                                continue; // Don't add anything for this import.
                            }
                            else if (alias == null && !typeSymbol.IsStatic)
                            {
                                // Only static types can be directly imported.
                                continue;
                            }

                            NameSyntax typeSyntax = SyntaxFactory.ParseName(typeSymbol.ToDisplayString(s_fullNameFormat));
                            if (!TryAddImport(alias, typeSyntax, typeSymbol, usingsBuilder, usingAliases, binder, importString))
                            {
                                continue;
                            }

                            break;
                        }
                    case ImportTargetKind.Namespace:
                        {
                            Debug.Assert(target != null, string.Format("Namespace import string '{0}' has no target", importString));

                            NameSyntax targetSyntax;
                            if (!SyntaxHelpers.TryParseDottedName(target, out targetSyntax))
//.........这里部分代码省略.........

 public BoundTypeExpression(SyntaxNode syntax, AliasSymbol aliasOpt, TypeSymbol type, bool hasErrors = false)
     : this(syntax, aliasOpt, false, null, type, hasErrors)
 {
 }

 public AliasAndUsingDirective(AliasSymbol alias, UsingDirectiveSyntax usingDirective)
 {
     this.Alias = alias;
     this.UsingDirective = usingDirective;
 }

 /// <summary>
 /// Creates an AttributeSemanticModel that allows asking semantic questions about an attribute node.
 /// </summary>
 public static AttributeSemanticModel Create(CSharpCompilation compilation, AttributeSyntax syntax, NamedTypeSymbol attributeType, AliasSymbol aliasOpt, Binder rootBinder)
 {
     var executableBinder = new ExecutableCodeBinder(syntax, attributeType, rootBinder);
     return new AttributeSemanticModel(compilation, syntax, attributeType, aliasOpt, new LocalScopeBinder(executableBinder));
 }

 public virtual void VisitAlias(AliasSymbol symbol)
 {
     DefaultVisit(symbol);
 }

 private AttributeSemanticModel(CSharpCompilation compilation, AttributeSyntax syntax, NamedTypeSymbol attributeType, AliasSymbol aliasOpt, Binder rootBinder, SyntaxTreeSemanticModel parentSemanticModelOpt = null, int speculatedPosition = 0)
     : base(compilation, syntax, attributeType, new ExecutableCodeBinder(syntax, rootBinder.ContainingMember(), rootBinder), parentSemanticModelOpt, speculatedPosition)
 {
     Debug.Assert(syntax != null);
     _aliasOpt = aliasOpt;
 }