Add support for C# 7.3 Attributes on backing fields: Allows [field: …] attributes on an auto-implemented property to target its backing field.

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

@@ -1,4 +1,6 @@
-namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+using System;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
 	// TODO : maybe use single-line formatting in this case?
 	internal class AutoProperties
@@ -20,5 +22,12 @@
 			get;
 			set;
 		} = 4;
+
+		[Obsolete("Property")]
+		[field: Obsolete("Field")]
+		public int PropertyWithAttributeOnBackingField {
+			get;
+			set;
+		}
 	}
 }

ICSharpCode.Decompiler.Tests/TestCases/Pretty/AutoProperties.opt.roslyn.il

@@ -44,6 +44,9 @@
   .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
   .field private static int32 '<D>k__BackingField'
   .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
+  .field private int32 '<PropertyWithAttributeOnBackingField>k__BackingField'
+  .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
+  .custom instance void [mscorlib]System.ObsoleteAttribute::.ctor(string) = ( 01 00 05 46 69 65 6C 64 00 00 )                   // ...Field..
   .method public hidebysig specialname instance int32 
           get_A() cil managed
   {
@@ -109,6 +112,29 @@
     IL_0006:  ret
   } // end of method AutoProperties::set_D
 
+  .method public hidebysig specialname instance int32 
+          get_PropertyWithAttributeOnBackingField() cil managed
+  {
+    .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
+    // Code size       7 (0x7)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  ldfld      int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::'<PropertyWithAttributeOnBackingField>k__BackingField'
+    IL_0006:  ret
+  } // end of method AutoProperties::get_PropertyWithAttributeOnBackingField
+
+  .method public hidebysig specialname instance void 
+          set_PropertyWithAttributeOnBackingField(int32 'value') cil managed
+  {
+    .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
+    // Code size       8 (0x8)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  ldarg.1
+    IL_0002:  stfld      int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::'<PropertyWithAttributeOnBackingField>k__BackingField'
+    IL_0007:  ret
+  } // end of method AutoProperties::set_PropertyWithAttributeOnBackingField
+
   .method public hidebysig specialname rtspecialname 
           instance void  .ctor() cil managed
   {
@@ -155,6 +181,12 @@
     .get int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::get_D()
     .set void ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::set_D(int32)
   } // end of property AutoProperties::D
+  .property instance int32 PropertyWithAttributeOnBackingField()
+  {
+    .custom instance void [mscorlib]System.ObsoleteAttribute::.ctor(string) = ( 01 00 08 50 72 6F 70 65 72 74 79 00 00 )          // ...Property..
+    .get instance int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::get_PropertyWithAttributeOnBackingField()
+    .set instance void ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::set_PropertyWithAttributeOnBackingField(int32)
+  } // end of property AutoProperties::PropertyWithAttributeOnBackingField
 } // end of class ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties
 
 

ICSharpCode.Decompiler.Tests/TestCases/Pretty/AutoProperties.roslyn.il

@@ -48,6 +48,10 @@
   .field private static int32 '<D>k__BackingField'
   .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
   .custom instance void [mscorlib]System.Diagnostics.DebuggerBrowsableAttribute::.ctor(valuetype [mscorlib]System.Diagnostics.DebuggerBrowsableState) = ( 01 00 00 00 00 00 00 00 ) 
+  .field private int32 '<PropertyWithAttributeOnBackingField>k__BackingField'
+  .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
+  .custom instance void [mscorlib]System.Diagnostics.DebuggerBrowsableAttribute::.ctor(valuetype [mscorlib]System.Diagnostics.DebuggerBrowsableState) = ( 01 00 00 00 00 00 00 00 ) 
+  .custom instance void [mscorlib]System.ObsoleteAttribute::.ctor(string) = ( 01 00 05 46 69 65 6C 64 00 00 )                   // ...Field..
   .method public hidebysig specialname instance int32 
           get_A() cil managed
   {
@@ -113,6 +117,29 @@
     IL_0006:  ret
   } // end of method AutoProperties::set_D
 
+  .method public hidebysig specialname instance int32 
+          get_PropertyWithAttributeOnBackingField() cil managed
+  {
+    .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
+    // Code size       7 (0x7)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  ldfld      int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::'<PropertyWithAttributeOnBackingField>k__BackingField'
+    IL_0006:  ret
+  } // end of method AutoProperties::get_PropertyWithAttributeOnBackingField
+
+  .method public hidebysig specialname instance void 
+          set_PropertyWithAttributeOnBackingField(int32 'value') cil managed
+  {
+    .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
+    // Code size       8 (0x8)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  ldarg.1
+    IL_0002:  stfld      int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::'<PropertyWithAttributeOnBackingField>k__BackingField'
+    IL_0007:  ret
+  } // end of method AutoProperties::set_PropertyWithAttributeOnBackingField
+
   .method public hidebysig specialname rtspecialname 
           instance void  .ctor() cil managed
   {
@@ -160,6 +187,12 @@
     .get int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::get_D()
     .set void ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::set_D(int32)
   } // end of property AutoProperties::D
+  .property instance int32 PropertyWithAttributeOnBackingField()
+  {
+    .custom instance void [mscorlib]System.ObsoleteAttribute::.ctor(string) = ( 01 00 08 50 72 6F 70 65 72 74 79 00 00 )          // ...Property..
+    .get instance int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::get_PropertyWithAttributeOnBackingField()
+    .set instance void ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties::set_PropertyWithAttributeOnBackingField(int32)
+  } // end of property AutoProperties::PropertyWithAttributeOnBackingField
 } // end of class ICSharpCode.Decompiler.Tests.TestCases.Pretty.AutoProperties
 
 

ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs

@@ -510,6 +510,17 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				property.Getter.Body = null;
 				property.Setter.Body = null;
 			}
+			// Add C# 7.3 attributes on backing field:
+			var attributes = fieldInfo.Attributes
+				.Where(a => !attributeTypesToRemoveFromAutoProperties.Any(t => t == a.AttributeType.FullName))
+				.Select(context.TypeSystemAstBuilder.ConvertAttribute).ToArray();
+			if (attributes.Length > 0) {
+				var section = new AttributeSection {
+					AttributeTarget = "field"
+				};
+				section.Attributes.AddRange(attributes);
+				property.Attributes.Add(section);
+			}
 			// Since the property instance is not changed, we can continue in the visitor as usual, so return null
 			return null;
 		}
@@ -706,6 +717,11 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			"System.Runtime.CompilerServices.MethodImplAttribute"
 		};
 
+		static readonly string[] attributeTypesToRemoveFromAutoProperties = new[] {
+			"System.Runtime.CompilerServices.CompilerGeneratedAttribute",
+			"System.Diagnostics.DebuggerBrowsableAttribute"
+		};
+
 		bool CheckAutomaticEventV4(CustomEventDeclaration ev, out Match addMatch, out Match removeMatch)
 		{
 			addMatch = removeMatch = default(Match);