From d3f2156a8cfb3d2696de2f289ffdb308a076bb73 Mon Sep 17 00:00:00 2001
From: Cyrus Najmabadi <cyrus.najmabadi@gmail.com>
Date: Tue, 22 Jul 2025 14:03:44 +0200
Subject: [PATCH] Allow captured primary constructor parameters to be still
 used in base-list

---
 .../CSharpCompletionCommandHandlerTests.vb    | 21 +++++++++++++++++++
 .../CSharpRecommendationServiceRunner.cs      |  7 ++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/EditorFeatures/Test2/IntelliSense/CSharpCompletionCommandHandlerTests.vb b/src/EditorFeatures/Test2/IntelliSense/CSharpCompletionCommandHandlerTests.vb
index 961a3ecc70c95..7e753857124d4 100644
--- a/src/EditorFeatures/Test2/IntelliSense/CSharpCompletionCommandHandlerTests.vb
+++ b/src/EditorFeatures/Test2/IntelliSense/CSharpCompletionCommandHandlerTests.vb
@@ -11931,6 +11931,27 @@ public class C(int x) : Base(x)
             End Using
         End Function
 
+        <WpfFact, WorkItem("https://github.com/dotnet/roslyn/issues/78917")>
+        Public Async Function FilterPrimaryConstructorParameters_AllowInBaseTypeWhenCapturedAsMember() As Task
+            Using state = TestStateFactory.CreateCSharpTestState(
+                <Document><![CDATA[
+public sealed class Derived(
+    string value)
+    : Base($"{val$$}")
+{
+    public string Value { get; } = value;
+}
+
+public abstract class Base(string value);
+]]>
+                </Document>,
+                languageVersion:=LanguageVersion.CSharp12)
+
+                state.SendInvokeCompletionList()
+                Await state.AssertCompletionItemsContain("value", displayTextSuffix:="")
+            End Using
+        End Function
+
         <WpfFact, Trait(Traits.Feature, Traits.Features.Completion)>
         Public Async Function TestItemsSorted() As Task
             Using state = TestStateFactory.CreateCSharpTestState(
diff --git a/src/Workspaces/CSharp/Portable/Recommendations/CSharpRecommendationServiceRunner.cs b/src/Workspaces/CSharp/Portable/Recommendations/CSharpRecommendationServiceRunner.cs
index 58bccf1e2827e..b9519345df8ea 100644
--- a/src/Workspaces/CSharp/Portable/Recommendations/CSharpRecommendationServiceRunner.cs
+++ b/src/Workspaces/CSharp/Portable/Recommendations/CSharpRecommendationServiceRunner.cs
@@ -443,7 +443,7 @@ static bool IsCapturedPrimaryConstructorParameter(
                 CancellationToken cancellationToken)
             {
                 // Fine to offer primary constructor parameters in field/property initializers 
-                var initializer = context.TargetToken.GetAncestors<EqualsValueClauseSyntax>().FirstOrDefault();
+                var initializer = context.TargetToken.GetAncestor<EqualsValueClauseSyntax>();
                 if (initializer is
                     {
                         Parent: PropertyDeclarationSyntax or
@@ -453,6 +453,11 @@ static bool IsCapturedPrimaryConstructorParameter(
                     return false;
                 }
 
+                // Also fine to offer primary constructor parameters in the base type list of that type.
+                var baseTypeSyntax = context.TargetToken.GetAncestor<PrimaryConstructorBaseTypeSyntax>();
+                if (baseTypeSyntax != null)
+                    return false;
+
                 // We're not in an initializer.  Filter out this primary constructor parameter if it's already been
                 // captured by an existing field or property initializer.