Fix #2406: for readonly property with only getter, move readonly to property instead of getter

ICSharpCode.Decompiler.Tests/TestCases/Pretty/RefLocalsAndReturns.cs

@@ -98,6 +98,13 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				}
 			}
 
+			public readonly int ReadOnlyPropertyWithOnlyGetter {
+				get {
+					Console.WriteLine("No inlining");
+					return 1;
+				}
+			}
+
 			public ref int RefProperty => ref arr[0];
 			public ref readonly int RefReadonlyProperty => ref arr[0];
 			public readonly ref int ReadonlyRefProperty => ref arr[0];

ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs

@@ -2035,7 +2035,12 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		static void MergeReadOnlyModifiers(EntityDeclaration decl, Accessor accessor1, Accessor accessor2)
 		{
-			if (accessor1.HasModifier(Modifiers.Readonly) && accessor2.HasModifier(Modifiers.Readonly))
+			if (accessor1.HasModifier(Modifiers.Readonly) && accessor1.Role == PropertyDeclaration.GetterRole && accessor2.IsNull)
+			{
+				accessor1.Modifiers &= ~Modifiers.Readonly;
+				decl.Modifiers |= Modifiers.Readonly;
+			}
+			else if (accessor1.HasModifier(Modifiers.Readonly) && accessor2.HasModifier(Modifiers.Readonly))
 			{
 				accessor1.Modifiers &= ~Modifiers.Readonly;
 				accessor2.Modifiers &= ~Modifiers.Readonly;

ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs

@@ -630,7 +630,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 			if (field == null || !NameCouldBeBackingFieldOfAutomaticProperty(field.Name, out _))
 				return null;
-			if (propertyDeclaration.Setter.HasModifier(Modifiers.Readonly))
+			if (propertyDeclaration.Setter.HasModifier(Modifiers.Readonly) || (propertyDeclaration.HasModifier(Modifiers.Readonly) && !propertyDeclaration.Setter.IsNull))
 				return null;
 			if (field.IsCompilerGenerated() && field.DeclaringTypeDefinition == property.DeclaringTypeDefinition)
 			{
@@ -638,6 +638,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				RemoveCompilerGeneratedAttribute(propertyDeclaration.Setter.Attributes);
 				propertyDeclaration.Getter.Body = null;
 				propertyDeclaration.Setter.Body = null;
+				propertyDeclaration.Modifiers &= ~Modifiers.Readonly;
 				propertyDeclaration.Getter.Modifiers &= ~Modifiers.Readonly;
 
 				// Add C# 7.3 attributes on backing field: