Merge pull request #41371 from y87feng/40967

Introduce explicit downcast refactoring if a variable requires a cast to compile

src/Analyzers/Core/CodeFixes/PredefinedCodeFixProviderNames.cs

@@ -72,5 +72,6 @@ internal static class PredefinedCodeFixProviderNames
         public const string UseThrowExpression = nameof(UseThrowExpression);
         public const string PreferFrameworkType = nameof(PreferFrameworkType);
         public const string MakeStructFieldsWritable = nameof(MakeStructFieldsWritable);
+        public const string AddExplicitCast = nameof(AddExplicitCast);
     }
 }

src/Features/CSharp/Portable/CSharpFeaturesResources.resx

@@ -643,6 +643,12 @@
     <value>Reverse 'for' statement</value>
     <comment>{Locked="for"} "for" is a C# keyword and should not be localized.</comment>
   </data>
+  <data name="Add_explicit_cast" xml:space="preserve">
+    <value>Add explicit cast</value>
+  </data>
+  <data name="Convert_type_to_0" xml:space="preserve">
+    <value>Convert type to '{0}'</value>
+  </data>
   <data name="Convert_to_regular_string" xml:space="preserve">
     <value>Convert to regular string</value>
   </data>

src/Features/CSharp/Portable/CodeFixes/AddExplicitCast/InheritanceDistanceComparer.cs

+// 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 enable
+
+using System;
+using System.Collections.Generic;
+
+namespace Microsoft.CodeAnalysis.CSharp.CodeFixes.AddExplicitCast
+{
+    /// <summary>
+    /// Sort types by inheritance distance from the base type in ascending order, i.e., less specific type 
+    /// has higher priority because it has less probability to make mistakes
+    /// <para/>
+    /// For example:
+    /// class Base { }
+    /// class Derived1 : Base { }
+    /// class Derived2 : Derived1 { }
+    /// 
+    /// void Foo(Derived1 d1) { }
+    /// void Foo(Derived2 d2) { }
+    /// 
+    /// Base b = new Derived1();
+    /// Foo([||]b);
+    /// 
+    /// operations:
+    /// 1. Convert type to 'Derived1'
+    /// 2. Convert type to 'Derived2'
+    /// 
+    /// 'Derived1' is less specific than 'Derived2' compared to 'Base'
+    /// </summary>
+    internal sealed class InheritanceDistanceComparer : IComparer<ITypeSymbol>
+    {
+        private readonly ITypeSymbol _baseType;
+        private readonly SemanticModel _semanticModel;
+
+        public InheritanceDistanceComparer(SemanticModel semanticModel, ITypeSymbol baseType)
+        {
+            _semanticModel = semanticModel;
+            _baseType = baseType;
+        }
+
+        public int Compare(ITypeSymbol x, ITypeSymbol y)
+        {
+            var xDist = GetInheritanceDistance(x);
+            var yDist = GetInheritanceDistance(y);
+            return xDist.CompareTo(yDist);
+        }
+
+        /// <summary>
+        /// Calculate the inheritance distance between _baseType and derivedType.
+        /// </summary>
+        private int GetInheritanceDistanceRecursive(ITypeSymbol? derivedType)
+        {
+            if (derivedType == null)
+                return int.MaxValue;
+            if (derivedType.Equals(_baseType))
+                return 0;
+
+            var distance = GetInheritanceDistanceRecursive(derivedType.BaseType);
+
+            if (derivedType.Interfaces.Length != 0)
+            {
+                foreach (var interfaceType in derivedType.Interfaces)
+                {
+                    distance = Math.Min(GetInheritanceDistanceRecursive(interfaceType), distance);
+                }
+            }
+
+            return distance == int.MaxValue ? distance : distance + 1;
+        }
+
+        /// <summary>
+        /// Wrapper funtion of [GetInheritanceDistance], also consider the class with explicit conversion operator
+        /// has the highest priority.
+        /// </summary>
+        private int GetInheritanceDistance(ITypeSymbol type)
+        {
+            var conversion = _semanticModel.Compilation.ClassifyCommonConversion(_baseType, type);
+
+            // If the node has the explicit conversion operator, then it has the shortest distance
+            // since explicit conversion operator is defined by users and has the highest priority 
+            var distance = conversion.IsUserDefined ? 0 : GetInheritanceDistanceRecursive(type);
+            return distance;
+        }
+    }
+}

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.cs.xlf

@@ -12,6 +12,11 @@
         <target state="translated">Přidat await</target>
         <note />
       </trans-unit>
+      <trans-unit id="Add_explicit_cast">
+        <source>Add explicit cast</source>
+        <target state="new">Add explicit cast</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Add_missing_usings">
         <source>Add missing usings</source>
         <target state="translated">Přidat chybějící direktivy using</target>
@@ -92,6 +97,11 @@
         <target state="new">Convert to verbatim string</target>
         <note />
       </trans-unit>
+      <trans-unit id="Convert_type_to_0">
+        <source>Convert type to '{0}'</source>
+        <target state="new">Convert type to '{0}'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Declare_as_nullable">
         <source>Declare as nullable</source>
         <target state="translated">Deklarovat jako s možnou hodnotou null</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.de.xlf

@@ -12,6 +12,11 @@
         <target state="translated">"await" hinzufügen</target>
         <note />
       </trans-unit>
+      <trans-unit id="Add_explicit_cast">
+        <source>Add explicit cast</source>
+        <target state="new">Add explicit cast</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Add_missing_usings">
         <source>Add missing usings</source>
         <target state="translated">Fehlende using-Anweisungen hinzufügen</target>
@@ -92,6 +97,11 @@
         <target state="new">Convert to verbatim string</target>
         <note />
       </trans-unit>
+      <trans-unit id="Convert_type_to_0">
+        <source>Convert type to '{0}'</source>
+        <target state="new">Convert type to '{0}'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Declare_as_nullable">
         <source>Declare as nullable</source>
         <target state="translated">Als für NULL-Werte zulässig deklarieren</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.es.xlf

@@ -12,6 +12,11 @@
         <target state="translated">Añadir await</target>
         <note />
       </trans-unit>
+      <trans-unit id="Add_explicit_cast">
+        <source>Add explicit cast</source>
+        <target state="new">Add explicit cast</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Add_missing_usings">
         <source>Add missing usings</source>
         <target state="translated">Añadir valores using que faltan</target>
@@ -92,6 +97,11 @@
         <target state="new">Convert to verbatim string</target>
         <note />
       </trans-unit>
+      <trans-unit id="Convert_type_to_0">
+        <source>Convert type to '{0}'</source>
+        <target state="new">Convert type to '{0}'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Declare_as_nullable">
         <source>Declare as nullable</source>
         <target state="translated">Declara como que acepta valores NULL</target>

src/Features/CSharp/Portable/xlf/CSharpFeaturesResources.fr.xlf

@@ -12,6 +12,11 @@
         <target state="translated">Ajouter une expression await</target>
         <note />
       </trans-unit>
+      <trans-unit id="Add_explicit_cast">
+        <source>Add explicit cast</source>
+        <target state="new">Add explicit cast</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Add_missing_usings">
         <source>Add missing usings</source>
         <target state="translated">Ajouter les instructions using manquantes</target>
@@ -92,6 +97,11 @@
         <target state="new">Convert to verbatim string</target>
         <note />
       </trans-unit>
+      <trans-unit id="Convert_type_to_0">
+        <source>Convert type to '{0}'</source>
+        <target state="new">Convert type to '{0}'</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Declare_as_nullable">
         <source>Declare as nullable</source>
         <target state="translated">Déclarer comme nullable</target>

src/Test/Utilities/Portable/Traits/Traits.cs

@@ -40,6 +40,7 @@ public static class Features
             public const string CodeActionsAddBraces = "CodeActions.AddBraces";
             public const string CodeActionsAddConstructorParametersFromMembers = "CodeActions.AddConstructorParametersFromMembers";
             public const string CodeActionsAddDocCommentNodes = "CodeActions.AddDocCommentParamNodes";
+            public const string CodeActionsAddExplicitCast = "CodeActions.AddExplicitCast";
             public const string CodeActionsAddFileBanner = "CodeActions.AddFileBanner";
             public const string CodeActionsAddImport = "CodeActions.AddImport";
             public const string CodeActionsAddMissingReference = "CodeActions.AddMissingReference";

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Log/FunctionId.cs

@@ -475,5 +475,7 @@ internal enum FunctionId
 
         LanguageServer_ActivateFailed = 382,
         LanguageServer_OnLoadedFailed = 383,
+
+        CodeFixes_AddExplicitCast = 384,
     }
 }