Workaround for #31381, which seems to be causing duplicate diagnostics being passed to FixAll

src/Workspaces/Core/Portable/CodeFixes/SyntaxEditorBasedCodeFixProvider.FixAllProvider.cs

@@ -64,7 +64,10 @@ public sealed override async Task<CodeAction> GetFixAsync(FixAllContext fixAllCo
                 // Ensure that diagnostics for this document are always in document location
                 // order.  This provides a consistent and deterministic order for fixers
                 // that want to update a document.
-                var filteredDiagnostics = diagnostics.WhereAsArray(d => _codeFixProvider.IncludeDiagnosticDuringFixAll(fixAllState, d, cancellationToken))
+                // Also ensure that we do not pass in duplicates by invoking Distinct.
+                // See https://github.com/dotnet/roslyn/issues/31381, that seems to be causing duplicate diagnostics.
+                var filteredDiagnostics = diagnostics.Distinct()
+                                                     .WhereAsArray(d => _codeFixProvider.IncludeDiagnosticDuringFixAll(fixAllState, d, cancellationToken))
                                                      .Sort((d1, d2) => d1.Location.SourceSpan.Start - d2.Location.SourceSpan.Start);
 
                 // PERF: Do not invoke FixAllAsync on the code fix provider if there are no diagnostics to be fixed.