Follow up on CR feedback.

Fixes #9624.

src/Compilers/CSharp/Portable/Binder/Binder.cs

@@ -778,7 +778,8 @@ internal Binder WithPatternVariablesIfAny(ArgumentListSyntax initializerArgument
             CSharpSyntaxNode node = null,
             ImmutableArray<CSharpSyntaxNode> nodes = default(ImmutableArray<CSharpSyntaxNode>))
         {
-            var patterns = PatternVariableFinder.FindPatternVariables(node, nodes);
+            var patterns = ArrayBuilder<DeclarationPatternSyntax>.GetInstance();
+            PatternVariableFinder.FindPatternVariables(patterns, node, nodes);
             foreach (var pattern in patterns)
             {
                 builder.Add(SourceLocalSymbol.MakeLocal(ContainingMemberOrLambda, this, RefKind.None, pattern.Type, pattern.Identifier, LocalDeclarationKind.PatternVariable));

src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs

@@ -796,9 +796,9 @@ private TypeSymbol BindVariableType(CSharpSyntaxNode declarationNode, Diagnostic
             // Step out of the PatternVariableBinder for locals declared in variable declaration statement
             if (this is PatternVariableBinder)
             {
-                CSharpSyntaxNode parent;
-                if ((parent = declarator.Parent)?.Kind() == SyntaxKind.VariableDeclaration &&
-                     parent.Parent?.Kind() == SyntaxKind.LocalDeclarationStatement)
+                CSharpSyntaxNode parent = declarator.Parent;
+                if (parent?.Kind() == SyntaxKind.VariableDeclaration &&
+                    parent.Parent?.Kind() == SyntaxKind.LocalDeclarationStatement)
                 {
                     nameConflictChecker = this.Next;
                 }

src/Compilers/CSharp/Portable/Binder/PatternVariableFinder.cs

@@ -13,12 +13,14 @@ namespace Microsoft.CodeAnalysis.CSharp
     class PatternVariableFinder : CSharpSyntaxWalker
     {
         ArrayBuilder<DeclarationPatternSyntax> declarationPatterns;
-        internal static ArrayBuilder<DeclarationPatternSyntax> FindPatternVariables(
+
+        internal static void FindPatternVariables(
+            ArrayBuilder<DeclarationPatternSyntax> builder,
             CSharpSyntaxNode node = null,
             ImmutableArray<CSharpSyntaxNode> nodes = default(ImmutableArray<CSharpSyntaxNode>))
         {
             var finder = s_poolInstance.Allocate();
-            finder.declarationPatterns = ArrayBuilder<DeclarationPatternSyntax>.GetInstance();
+            finder.declarationPatterns = builder;
             finder.Visit(node);
             if (!nodes.IsDefaultOrEmpty)
             {
@@ -28,10 +30,8 @@ class PatternVariableFinder : CSharpSyntaxWalker
                 }
             }
 
-            var result = finder.declarationPatterns;
             finder.declarationPatterns = null;
             s_poolInstance.Free(finder);
-            return result;
         }
 
         public override void VisitDeclarationPattern(DeclarationPatternSyntax node)