Use language-specific string comparisons

src/EditorFeatures/VisualBasicTest/Completion/CompletionProviders/SymbolCompletionProviderTests.vb

@@ -8161,6 +8161,28 @@ End Class
             Await VerifyItemExistsAsync(source, "Length")
         End Function
 
+        <Fact, Trait(Traits.Feature, Traits.Features.Completion)>
+        <WorkItem(40216, "https://github.com/dotnet/roslyn/issues/40216")>
+        Public Async Function CompletionForLambdaPassedAsNamedArgumentAtDifferentPositionFromCorrespondingParameterWithDifferentCasing() As Task
+            Dim source =
+                <code><![CDATA[
+Imports System
+
+Class C
+    Sub Test()
+        M(Z:=Sub(x)
+                 x.$$
+          End Sub)
+    End Sub
+
+    Sub M(x As Integer, y As Integer, z As Action(Of String))
+    End Sub
+End Class
+]]></code>.Value
+
+            Await VerifyItemExistsAsync(source, "Length")
+        End Function
+
         <Fact, Trait(Traits.Feature, Traits.Features.Completion)>
         Public Async Function CompletionInsideMethodsWithNonFunctionsAsArguments() As Task
             Dim source =

src/Workspaces/Core/Portable/Recommendations/AbstractRecommendationServiceRunner.cs

@@ -19,6 +19,7 @@ internal abstract class AbstractRecommendationServiceRunner<TSyntaxContext>
         protected readonly TSyntaxContext _context;
         protected readonly bool _filterOutOfScopeLocals;
         protected readonly CancellationToken _cancellationToken;
+        private readonly StringComparer _stringComparerForLanguage;
 
         public AbstractRecommendationServiceRunner(
             TSyntaxContext context,
@@ -26,6 +27,7 @@ internal abstract class AbstractRecommendationServiceRunner<TSyntaxContext>
             CancellationToken cancellationToken)
         {
             _context = context;
+            _stringComparerForLanguage = _context.GetLanguageService<ISyntaxFactsService>().StringComparer;
             _filterOutOfScopeLocals = filterOutOfScopeLocals;
             _cancellationToken = cancellationToken;
         }
@@ -151,7 +153,7 @@ private bool TryGetMatchingParameterTypeForArgument(IMethodSymbol method, string
         {
             if (!string.IsNullOrEmpty(argumentName))
             {
-                parameterType = method.Parameters.FirstOrDefault(p => p.Name == argumentName)?.Type;
+                parameterType = method.Parameters.FirstOrDefault(p => _stringComparerForLanguage.Equals(p.Name, argumentName))?.Type;
                 return parameterType != null;
             }