Allow opening showing change signature for parameterless methods

src/Features/Core/Portable/ChangeSignature/AbstractChangeSignatureService.cs

@@ -136,7 +136,7 @@ internal ChangeSignatureResult ChangeSignature(Document document, int position,
                 return new ChangeSignatureAnalyzedContext(CannotChangeSignatureReason.IncorrectKind);
             }
 
-            var parameterConfiguration = ParameterConfiguration.Create(symbol.GetParameters().Select(p => new ExistingParameter(p)).ToList<CoolParameter>(), symbol is IMethodSymbol && (symbol as IMethodSymbol).IsExtensionMethod, selectedIndex);
+            var parameterConfiguration = ParameterConfiguration.Create(symbol.GetParameters().Select(p => new ExistingParameter(p)).ToList<ParameterBase>(), symbol is IMethodSymbol && (symbol as IMethodSymbol).IsExtensionMethod, selectedIndex);
             if (!parameterConfiguration.IsChangeable())
             {
                 return new ChangeSignatureAnalyzedContext(CannotChangeSignatureReason.InsufficientParameters);

src/Features/Core/Portable/ChangeSignature/CoolParameter.cs → src/Features/Core/Portable/ChangeSignature/ParameterBase.cs

@@ -2,14 +2,14 @@
 
 namespace Microsoft.CodeAnalysis.ChangeSignature
 {
-    internal abstract class CoolParameter
+    internal abstract class ParameterBase
     {
         public abstract bool HasExplicitDefaultValue { get; }
         public abstract string Name { get; }
         public abstract IParameterSymbol Symbol { get; }
     }
 
-    internal class ExistingParameter : CoolParameter
+    internal class ExistingParameter : ParameterBase
     {
         public override IParameterSymbol Symbol { get; }
 
@@ -22,7 +22,7 @@ public ExistingParameter(IParameterSymbol param)
         public override string Name => Symbol.Name;
     }
 
-    internal class AddedParameter : CoolParameter
+    internal class AddedParameter : ParameterBase
     {
         public AddedParameter(string type, string parameter, string callsite)
         {

src/Features/Core/Portable/ChangeSignature/ParameterConfiguration.cs

@@ -8,13 +8,13 @@ namespace Microsoft.CodeAnalysis.ChangeSignature
 {
     internal sealed class ParameterConfiguration
     {
-        public readonly CoolParameter ThisParameter;
-        public readonly List<CoolParameter> ParametersWithoutDefaultValues;
-        public readonly List<CoolParameter> RemainingEditableParameters;
-        public readonly CoolParameter ParamsParameter;
+        public readonly ParameterBase ThisParameter;
+        public readonly List<ParameterBase> ParametersWithoutDefaultValues;
+        public readonly List<ParameterBase> RemainingEditableParameters;
+        public readonly ParameterBase ParamsParameter;
         public readonly int SelectedIndex;
 
-        public ParameterConfiguration(CoolParameter thisParameter, List<CoolParameter> parametersWithoutDefaultValues, List<CoolParameter> remainingEditableParameters, CoolParameter paramsParameter, int selectedIndex)
+        public ParameterConfiguration(ParameterBase thisParameter, List<ParameterBase> parametersWithoutDefaultValues, List<ParameterBase> remainingEditableParameters, ParameterBase paramsParameter, int selectedIndex)
         {
             ThisParameter = thisParameter;
             ParametersWithoutDefaultValues = parametersWithoutDefaultValues;
@@ -23,12 +23,12 @@ public ParameterConfiguration(CoolParameter thisParameter, List<CoolParameter> p
             SelectedIndex = selectedIndex;
         }
 
-        public static ParameterConfiguration Create(List<CoolParameter> parameters, bool isExtensionMethod, int selectedIndex)
+        public static ParameterConfiguration Create(List<ParameterBase> parameters, bool isExtensionMethod, int selectedIndex)
         {
-            CoolParameter thisParameter = null;
-            var parametersWithoutDefaultValues = new List<CoolParameter>();
-            var remainingReorderableParameters = new List<CoolParameter>();
-            CoolParameter paramsParameter = null;
+            ParameterBase thisParameter = null;
+            var parametersWithoutDefaultValues = new List<ParameterBase>();
+            var remainingReorderableParameters = new List<ParameterBase>();
+            ParameterBase paramsParameter = null;
 
             if (parameters.Count > 0 && isExtensionMethod)
             {
@@ -58,12 +58,12 @@ public static ParameterConfiguration Create(List<CoolParameter> parameters, bool
 
         internal ParameterConfiguration WithoutAddedParameters()
         {
-            return Create(ToListOfParameters().OfType<ExistingParameter>().ToList<CoolParameter>(), ThisParameter != null, selectedIndex: 0);
+            return Create(ToListOfParameters().OfType<ExistingParameter>().ToList<ParameterBase>(), ThisParameter != null, selectedIndex: 0);
         }
 
-        public List<CoolParameter> ToListOfParameters()
+        public List<ParameterBase> ToListOfParameters()
         {
-            var list = new List<CoolParameter>();
+            var list = new List<ParameterBase>();
 
             if (ThisParameter != null)
             {
@@ -81,9 +81,11 @@ public List<CoolParameter> ToListOfParameters()
             return list;
         }
 
+        // TODO probably remove thiis check. It was created when we didn't support Add Parameters to parameterless methods.
         public bool IsChangeable()
         {
-            return ParametersWithoutDefaultValues.Count > 0 || RemainingEditableParameters.Count > 0 || ParamsParameter != null;
+            return true;
         }
     }
 }
+

src/VisualStudio/Core/Def/Implementation/ChangeSignature/ChangeSignatureDialogViewModel.cs

@@ -86,6 +86,11 @@ public bool CanRemove
         {
             get
             {
+                if (!AllParameters.Any())
+                {
+                    return false;
+                }
+
                 if (!SelectedIndex.HasValue)
                 {
                     return false;
@@ -108,6 +113,11 @@ public bool CanRestore
         {
             get
             {
+                if (!AllParameters.Any())
+                {
+                    return false;
+                }
+
                 if (!SelectedIndex.HasValue)
                 {
                     return false;
@@ -189,9 +199,9 @@ internal ParameterConfiguration GetParameterConfiguration()
         {
             return new ParameterConfiguration(
                 _originalParameterConfiguration.ThisParameter,
-                _parameterGroup1.Where(p => !p.IsRemoved).Select(p => p.MakeCoolParameter()).ToList(),
-                _parameterGroup2.Where(p => !p.IsRemoved).Select(p => p.MakeCoolParameter()).ToList(),
-                (_paramsParameter == null || _paramsParameter.IsRemoved) ? null : (_paramsParameter as ExistingParameterViewModel).MakeCoolParameter(),
+                _parameterGroup1.Where(p => !p.IsRemoved).Select(p => p.CreateParameter()).ToList(),
+                _parameterGroup2.Where(p => !p.IsRemoved).Select(p => p.CreateParameter()).ToList(),
+                (_paramsParameter == null || _paramsParameter.IsRemoved) ? null : (_paramsParameter as ExistingParameterViewModel).CreateParameter(),
                 selectedIndex: -1);
         }
 
@@ -513,7 +523,7 @@ public ParameterViewModel(ChangeSignatureDialogViewModel changeSignatureDialogVi
                 this.changeSignatureDialogViewModel = changeSignatureDialogViewModel;
             }
 
-            internal abstract CoolParameter MakeCoolParameter();
+            internal abstract ParameterBase CreateParameter();
 
             public abstract string InitialIndex { get; }
         }
@@ -538,10 +548,8 @@ public AddedParameterViewModel(ChangeSignatureDialogViewModel changeSignatureDia
             public override bool IsDisabled => false;
             public override string Callsite => _addParameterViewModel.CallsiteValue;
 
-            internal override CoolParameter MakeCoolParameter()
-            {
-                return new AddedParameter(Type, Parameter, Callsite);
-            }
+            internal override ParameterBase CreateParameter()
+                => new AddedParameter(Type, Parameter, Callsite);
 
             public override string InitialIndex => "NEW";
         }
@@ -550,14 +558,14 @@ public class ExistingParameterViewModel : ParameterViewModel
         {
             public IParameterSymbol ParameterSymbol { get; }
 
-            public ExistingParameterViewModel(ChangeSignatureDialogViewModel changeSignatureDialogViewModel, CoolParameter parameter, int initialIndex)
+            public ExistingParameterViewModel(ChangeSignatureDialogViewModel changeSignatureDialogViewModel, ParameterBase parameter, int initialIndex)
                 : base(changeSignatureDialogViewModel)
             {
                 ParameterSymbol = (parameter as ExistingParameter).Symbol;
                 InitialIndex = initialIndex.ToString();
             }
 
-            internal override CoolParameter MakeCoolParameter()
+            internal override ParameterBase CreateParameter()
             {
                 return new ExistingParameter(ParameterSymbol);
             }

src/VisualStudio/Core/Test/ChangeSignature/ChangeSignatureViewModelTests.vb

@@ -436,7 +436,7 @@ class MyClass
 
                 Dim viewModel = New ChangeSignatureDialogViewModel(
                     New TestNotificationService(),
-                    ParameterConfiguration.Create(symbol.GetParameters().Select(Function(p) DirectCast(New ExistingParameter(p), CoolParameter)).ToList(), symbol.IsExtensionMethod(), selectedIndex:=0),
+                    ParameterConfiguration.Create(symbol.GetParameters().Select(Function(p) DirectCast(New ExistingParameter(p), ParameterBase)).ToList(), symbol.IsExtensionMethod(), selectedIndex:=0),
                     symbol,
                     workspace.ExportProvider.GetExportedValue(Of IClassificationFormatMapService)().GetClassificationFormatMap("text"),
                     workspace.ExportProvider.GetExportedValue(Of ClassificationTypeMap)())