Update "use collection initializer" to use a collection-expression if the user prefers that form.

src/Analyzers/CSharp/Analyzers/CSharpAnalyzers.projitems

@@ -81,6 +81,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)UseCoalesceExpression\CSharpUseCoalesceExpressionForNullableTernaryConditionalCheckDiagnosticAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)UseCoalesceExpression\UseCoalesceExpressionHelpers.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)UseCollectionExpression\CSharpUseCollectionExpressionForArrayDiagnosticAnalyzer.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)UseCollectionExpression\UseCollectionExpressionHelpers.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)UseCompoundAssignment\CSharpUseCompoundAssignmentDiagnosticAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)UseCompoundAssignment\CSharpUseCompoundCoalesceAssignmentDiagnosticAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)UseCompoundAssignment\Utilities.cs" />

src/Analyzers/CSharp/Analyzers/UseCollectionExpression/CSharpUseCollectionExpressionForArrayDiagnosticAnalyzer.cs

@@ -4,29 +4,22 @@
 
 using System.Collections.Immutable;
 using System.Diagnostics;
-using System.Linq;
-using System.Threading;
 using Microsoft.CodeAnalysis.CodeStyle;
+using Microsoft.CodeAnalysis.CSharp.Analyzers.UseCollectionExpression;
 using Microsoft.CodeAnalysis.CSharp.Extensions;
 using Microsoft.CodeAnalysis.CSharp.Shared.Extensions;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.CSharp.Utilities;
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.Options;
-using Microsoft.CodeAnalysis.Shared.Collections;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis.CSharp.UseCollectionExpression;
 
-using static SyntaxFactory;
-
 [DiagnosticAnalyzer(LanguageNames.CSharp)]
 internal sealed partial class CSharpUseCollectionExpressionForArrayDiagnosticAnalyzer
     : AbstractBuiltInCodeStyleDiagnosticAnalyzer
 {
-    private static readonly LiteralExpressionSyntax s_nullLiteralExpression = LiteralExpression(SyntaxKind.NullLiteralExpression);
-
     public override DiagnosticAnalyzerCategory GetAnalyzerCategory()
         => DiagnosticAnalyzerCategory.SemanticSpanAnalysis;
 
@@ -56,7 +49,7 @@ protected override void InitializeWorker(AnalysisContext context)
 
     private void OnCompilationStart(CompilationStartAnalysisContext context)
     {
-        if (!context.Compilation.LanguageVersion().IsCSharp12OrAbove())
+        if (!context.Compilation.LanguageVersion().SupportsCollectionExpressions())
             return;
 
         // We wrap the SyntaxNodeAction within a CodeBlockStartAction, which allows us to
@@ -72,101 +65,6 @@ private void OnCompilationStart(CompilationStartAnalysisContext context)
         });
     }
 
-    private static bool IsInTargetTypedLocation(SemanticModel semanticModel, ExpressionSyntax expression, CancellationToken cancellationToken)
-    {
-        var topExpression = expression.WalkUpParentheses();
-        var parent = topExpression.Parent;
-        return parent switch
-        {
-            EqualsValueClauseSyntax equalsValue => IsInTargetTypedEqualsValueClause(equalsValue),
-            CastExpressionSyntax castExpression => IsInTargetTypedCastExpression(castExpression),
-            // a ? [1, 2, 3] : ...  is target typed if either the other side is *not* a collection,
-            // or the entire ternary is target typed itself.
-            ConditionalExpressionSyntax conditionalExpression => IsInTargetTypedConditionalExpression(conditionalExpression, topExpression),
-            // Similar rules for switches.
-            SwitchExpressionArmSyntax switchExpressionArm => IsInTargetTypedSwitchExpressionArm(switchExpressionArm),
-            InitializerExpressionSyntax initializerExpression => IsInTargetTypedInitializerExpression(initializerExpression, topExpression),
-            AssignmentExpressionSyntax assignmentExpression => IsInTargetTypedAssignmentExpression(assignmentExpression, topExpression),
-            BinaryExpressionSyntax binaryExpression => IsInTargetTypedBinaryExpression(binaryExpression, topExpression),
-            ArgumentSyntax or AttributeArgumentSyntax => true,
-            ReturnStatementSyntax => true,
-            _ => false,
-        };
-
-        bool HasType(ExpressionSyntax expression)
-            => semanticModel.GetTypeInfo(expression, cancellationToken).Type != null;
-
-        static bool IsInTargetTypedEqualsValueClause(EqualsValueClauseSyntax equalsValue)
-            // If we're after an `x = ...` and it's not `var x`, this is target typed.
-            => equalsValue.Parent is not VariableDeclaratorSyntax { Parent: VariableDeclarationSyntax { Type.IsVar: true } };
-
-        static bool IsInTargetTypedCastExpression(CastExpressionSyntax castExpression)
-            // (X[])[1, 2, 3] is target typed.  `(X)[1, 2, 3]` is currently not (because it looks like indexing into an expr).
-            => castExpression.Type is not IdentifierNameSyntax;
-
-        bool IsInTargetTypedConditionalExpression(ConditionalExpressionSyntax conditionalExpression, ExpressionSyntax expression)
-        {
-            if (conditionalExpression.WhenTrue == expression)
-                return HasType(conditionalExpression.WhenFalse) || IsInTargetTypedLocation(semanticModel, conditionalExpression, cancellationToken);
-            else if (conditionalExpression.WhenFalse == expression)
-                return HasType(conditionalExpression.WhenTrue) || IsInTargetTypedLocation(semanticModel, conditionalExpression, cancellationToken);
-            else
-                return false;
-        }
-
-        bool IsInTargetTypedSwitchExpressionArm(SwitchExpressionArmSyntax switchExpressionArm)
-        {
-            var switchExpression = (SwitchExpressionSyntax)switchExpressionArm.GetRequiredParent();
-
-            // check if any other arm has a type that this would be target typed against.
-            foreach (var arm in switchExpression.Arms)
-            {
-                if (arm != switchExpressionArm && HasType(arm.Expression))
-                    return true;
-            }
-
-            // All arms do not have a type, this is target typed if the switch itself is target typed.
-            return IsInTargetTypedLocation(semanticModel, switchExpression, cancellationToken);
-        }
-
-        bool IsInTargetTypedInitializerExpression(InitializerExpressionSyntax initializerExpression, ExpressionSyntax expression)
-        {
-            // new X[] { [1, 2, 3] }.  Elements are target typed by array type.
-            if (initializerExpression.Parent is ArrayCreationExpressionSyntax)
-                return true;
-
-            // new [] { [1, 2, 3], ... }.  Elements are target typed if there's another element with real type.
-            if (initializerExpression.Parent is ImplicitArrayCreationExpressionSyntax)
-            {
-                foreach (var sibling in initializerExpression.Expressions)
-                {
-                    if (sibling != expression && HasType(sibling))
-                        return true;
-                }
-            }
-
-            // TODO: Handle these.
-            if (initializerExpression.Parent is StackAllocArrayCreationExpressionSyntax or ImplicitStackAllocArrayCreationExpressionSyntax)
-                return false;
-
-            // T[] x = [1, 2, 3];
-            if (initializerExpression.Parent is EqualsValueClauseSyntax)
-                return true;
-
-            return false;
-        }
-
-        bool IsInTargetTypedAssignmentExpression(AssignmentExpressionSyntax assignmentExpression, ExpressionSyntax expression)
-        {
-            return expression == assignmentExpression.Right && HasType(assignmentExpression.Left);
-        }
-
-        bool IsInTargetTypedBinaryExpression(BinaryExpressionSyntax binaryExpression, ExpressionSyntax expression)
-        {
-            return binaryExpression.Kind() == SyntaxKind.CoalesceExpression && binaryExpression.Right == expression && HasType(binaryExpression.Left);
-        }
-    }
-
     private static void AnalyzeArrayInitializer(SyntaxNodeAnalysisContext context)
     {
         var semanticModel = context.SemanticModel;
@@ -179,72 +77,38 @@ private static void AnalyzeArrayInitializer(SyntaxNodeAnalysisContext context)
         if (!option.Value)
             return;
 
-        if (initializer.GetDiagnostics().Any(d => d.Severity == DiagnosticSeverity.Error))
-            return;
-
-        var parent = initializer.GetRequiredParent();
-        var topmostExpression = parent is ExpressionSyntax parentExpression
-            ? parentExpression.WalkUpParentheses()
-            : initializer.WalkUpParentheses();
+        var isConcreteOrImplicitArrayCreation = initializer.Parent is ArrayCreationExpressionSyntax or ImplicitArrayCreationExpressionSyntax;
 
-        if (!IsInTargetTypedLocation(semanticModel, topmostExpression, cancellationToken))
+        // a naked `{ ... }` can only be converted to a collection expression when in the exact form `x = { ... }`
+        if (!isConcreteOrImplicitArrayCreation && initializer.Parent is not EqualsValueClauseSyntax)
             return;
 
-        var isConcreteOrImplicitArrayCreation = parent is ArrayCreationExpressionSyntax or ImplicitArrayCreationExpressionSyntax;
-        if (isConcreteOrImplicitArrayCreation)
-        {
-            // X[] = new Y[] { 1, 2, 3 }
-            //
-            // First, we don't change things if X and Y are different.  That could lead to something observable at
-            // runtime in the case of something like:  object[] x = new string[] ...
-
-            var typeInfo = semanticModel.GetTypeInfo(parent, cancellationToken);
-            if (typeInfo.Type is null or IErrorTypeSymbol ||
-                typeInfo.ConvertedType is null or IErrorTypeSymbol)
-            {
-                return;
-            }
+        var arrayCreationExpression = isConcreteOrImplicitArrayCreation
+            ? (ExpressionSyntax)initializer.GetRequiredParent()
+            : initializer;
 
-            if (!typeInfo.Type.Equals(typeInfo.ConvertedType))
-                return;
-        }
-        else if (parent is not EqualsValueClauseSyntax)
+        if (!UseCollectionExpressionHelpers.CanReplaceWithCollectionExpression(
+                semanticModel, arrayCreationExpression, cancellationToken))
         {
             return;
         }
 
-        // Looks good as something to replace.  Now check the semantics of making the replacement to see if there would
-        // any issues.  To keep things simple, all we do is replace the existing expression with the `null` literal.
-        // This is a similarly 'untyped' literal (like a collection-expression is), so it tells us if the new code will
-        // have any issues moving to something untyped.  This will also tell us if we have any ambiguities (because
-        // there are multiple destination types that could accept the collection expression).
-        var speculationAnalyzer = new SpeculationAnalyzer(
-            topmostExpression,
-            s_nullLiteralExpression,
-            semanticModel,
-            cancellationToken,
-            skipVerificationForReplacedNode: true,
-            failOnOverloadResolutionFailuresInOriginalCode: true);
-
-        if (speculationAnalyzer.ReplacementChangesSemantics())
-            return;
-
         if (isConcreteOrImplicitArrayCreation)
         {
             var locations = ImmutableArray.Create(initializer.GetLocation());
             context.ReportDiagnostic(DiagnosticHelper.Create(
                 s_descriptor,
-                parent.GetFirstToken().GetLocation(),
+                arrayCreationExpression.GetFirstToken().GetLocation(),
                 option.Notification.Severity,
                 additionalLocations: locations,
                 properties: null));
 
             var additionalUnnecessaryLocations = ImmutableArray.Create(
                 syntaxTree.GetLocation(TextSpan.FromBounds(
-                    parent.SpanStart,
-                    parent is ArrayCreationExpressionSyntax arrayCreation
+                    arrayCreationExpression.SpanStart,
+                    arrayCreationExpression is ArrayCreationExpressionSyntax arrayCreation
                         ? arrayCreation.Type.Span.End
-                        : ((ImplicitArrayCreationExpressionSyntax)parent).CloseBracketToken.Span.End)));
+                        : ((ImplicitArrayCreationExpressionSyntax)arrayCreationExpression).CloseBracketToken.Span.End)));
 
             context.ReportDiagnostic(DiagnosticHelper.CreateWithLocationTags(
                 s_unnecessaryCodeDescriptor,
@@ -255,7 +119,7 @@ parent is ArrayCreationExpressionSyntax arrayCreation
         }
         else
         {
-            Debug.Assert(parent is EqualsValueClauseSyntax);
+            Debug.Assert(initializer.Parent is EqualsValueClauseSyntax);
             // int[] = { 1, 2, 3 };
             //
             // In this case, we always have a target type, so it should always be valid to convert this to a collection expression.