Prefix identifier with '@' if necessary

ChangeLog.md

@@ -29,6 +29,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Do not simplify default expression if it would change semantics ([RCS1244](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1244.md)) ([#939](https://github.com/josefpihrt/roslynator/pull/939).
 - Fix NullReferenceException in [RCS1198](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1198.md) ([#940](https://github.com/josefpihrt/roslynator/pull/940).
 - Order named arguments even if optional arguments are not specified [RCS1205](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1205.md) ([#941](https://github.com/josefpihrt/roslynator/pull/941).
+- Prefix identifier with `@` if necessary ([RCS1220](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1220.md)) ([#943](https://github.com/josefpihrt/roslynator/pull/943).
 
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 <!-- Content below does not adhere to 'Keep a Changelog' format -->

src/Analyzers.CodeFixes/CSharp/CodeFixes/UsePatternMatchingInsteadOfIsAndCastCodeFixProvider.cs

@@ -111,7 +111,7 @@ private static (IsPatternExpressionSyntax isPatternExpression, TNode newNode) Ge
 
             string name = NameGenerator.CreateName(typeSymbol, firstCharToLower: true) ?? DefaultNames.Variable;
 
-            name = NameGenerator.Default.EnsureUniqueLocalName(name, semanticModel, node.SpanStart, cancellationToken: cancellationToken) ?? DefaultNames.Variable;
+            name = CSharpNameGenerator.Default.EnsureUniqueLocalName(name, semanticModel, node.SpanStart, cancellationToken: cancellationToken) ?? DefaultNames.Variable;
 
             IsPatternExpressionSyntax isPatternExpression = IsPatternExpression(
                 isInfo.Expression,

src/CSharp/CSharp/CSharpNameGenerator.cs

@@ -0,0 +1,161 @@
+// Copyright (c) Josef Pihrt and Contributors. Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Threading;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+
+namespace Roslynator.CSharp
+{
+    //TODO: make public
+    /// <summary>
+    /// Provides methods to obtain an unique C# identifier.
+    /// </summary>
+    internal class CSharpNameGenerator
+    {
+        private static readonly NameGenerator _generator = new NumberSuffixCSharpNameGenerator();
+
+        /// <summary>
+        /// Default implementation of <see cref="CSharpNameGenerator"/> that adds number suffix to ensure uniqueness.
+        /// </summary>
+        public static CSharpNameGenerator Default { get; } = new();
+
+        /// <summary>
+        /// Returns a name that will be unique at the specified position.
+        /// </summary>
+        /// <param name="baseName"></param>
+        /// <param name="semanticModel"></param>
+        /// <param name="position"></param>
+        public string EnsureUniqueName(string baseName, SemanticModel semanticModel, int position)
+        {
+            return _generator.EnsureUniqueName(baseName, semanticModel, position);
+        }
+
+        /// <summary>
+        /// Returns unique enum member name for a specified enum type.
+        /// </summary>
+        /// <param name="baseName"></param>
+        /// <param name="enumType"></param>
+        public string EnsureUniqueEnumMemberName(string baseName, INamedTypeSymbol enumType)
+        {
+            return _generator.EnsureUniqueEnumMemberName(baseName, enumType, isCaseSensitive: true);
+        }
+
+        /// <summary>
+        /// Return a local name that will be unique at the specified position.
+        /// </summary>
+        /// <param name="baseName"></param>
+        /// <param name="semanticModel"></param>
+        /// <param name="position"></param>
+        /// <param name="cancellationToken"></param>
+        public string EnsureUniqueLocalName(
+            string baseName,
+            SemanticModel semanticModel,
+            int position,
+            CancellationToken cancellationToken = default)
+        {
+            return _generator.EnsureUniqueLocalName(baseName, semanticModel, position, isCaseSensitive: true, cancellationToken);
+        }
+
+        /// <summary>
+        /// Return a local names that will be unique at the specified position.
+        /// </summary>
+        /// <param name="baseName"></param>
+        /// <param name="semanticModel"></param>
+        /// <param name="position"></param>
+        /// <param name="count"></param>
+        /// <param name="cancellationToken"></param>
+        public ImmutableArray<string> EnsureUniqueLocalNames(
+            string baseName,
+            SemanticModel semanticModel,
+            int position,
+            int count,
+            CancellationToken cancellationToken = default)
+        {
+            return _generator.EnsureUniqueLocalNames(baseName, semanticModel, position, count, isCaseSensitive: true, cancellationToken);
+        }
+
+        /// <summary>
+        /// Return a parameter name that will be unique at the specified position.
+        /// </summary>
+        /// <param name="baseName"></param>
+        /// <param name="containingSymbol"></param>
+        /// <param name="semanticModel"></param>
+        /// <param name="cancellationToken"></param>
+        public string EnsureUniqueParameterName(
+            string baseName,
+            ISymbol containingSymbol,
+            SemanticModel semanticModel,
+            CancellationToken cancellationToken = default)
+        {
+            return _generator.EnsureUniqueParameterName(baseName, containingSymbol, semanticModel, isCaseSensitive: true, cancellationToken);
+        }
+
+        internal string CreateUniqueLocalName(
+            ITypeSymbol typeSymbol,
+            SemanticModel semanticModel,
+            int position,
+            CancellationToken cancellationToken = default)
+        {
+            return _generator.CreateUniqueLocalName(typeSymbol, semanticModel, position, isCaseSensitive: true, cancellationToken);
+        }
+
+        internal string CreateUniqueLocalName(
+            ITypeSymbol typeSymbol,
+            string oldName,
+            SemanticModel semanticModel,
+            int position,
+            CancellationToken cancellationToken = default)
+        {
+            return _generator.CreateUniqueLocalName(typeSymbol, oldName, semanticModel, position, isCaseSensitive: true, cancellationToken);
+        }
+
+        internal string CreateUniqueParameterName(
+            string oldName,
+            IParameterSymbol parameterSymbol,
+            SemanticModel semanticModel,
+            CancellationToken cancellationToken = default)
+        {
+            return _generator.CreateUniqueParameterName(oldName, parameterSymbol, semanticModel, isCaseSensitive: true, cancellationToken);
+        }
+
+        private class NumberSuffixCSharpNameGenerator : NameGenerator
+        {
+            public override string EnsureUniqueName(string baseName, IEnumerable<string> reservedNames, bool isCaseSensitive = true)
+            {
+                int suffix = 1;
+
+                string name = baseName;
+
+                while (!IsUniqueName(name, reservedNames, isCaseSensitive))
+                {
+                    suffix++;
+                    name = baseName + suffix.ToString();
+                }
+
+                return CheckKeyword(name);
+            }
+
+            public override string EnsureUniqueName(string baseName, ImmutableArray<ISymbol> symbols, bool isCaseSensitive = true)
+            {
+                int suffix = 1;
+
+                string name = baseName;
+
+                while (!IsUniqueName(name, symbols, isCaseSensitive))
+                {
+                    suffix++;
+                    name = baseName + suffix.ToString();
+                }
+
+                return CheckKeyword(name);
+            }
+
+            private string CheckKeyword(string name)
+            {
+                return (SyntaxFacts.GetKeywordKind(name) != SyntaxKind.None) ? "@" + name : name;
+            }
+        }
+    }
+}