[src/tools] Propagate the BackwardsCompatibleCodeGeneration field from Protocol attributes in bindings to the generated code. (#20804)

Also fix the MustSetBackwardsCompatibleCodeGenerationToFalse test to skip
protocols that actually set BackwardsCompatibleCodeGeneration=false.

src/bgen/Generator.cs

@@ -4879,11 +4879,13 @@ public partial class Generator : IMemberGatherer {
 		WriteDocumentation (type);
 
 		PrintAttributes (type, platform: true, preserve: true, advice: true);
-		print ("[Protocol (Name = \"{1}\", WrapperType = typeof ({0}Wrapper){2}{3})]",
+		print ("[Protocol (Name = \"{1}\", WrapperType = typeof ({0}Wrapper){2}{3}{4})]",
 			   TypeName,
 			   protocol_name,
 			   protocolAttribute.IsInformal ? ", IsInformal = true" : string.Empty,
-			   protocolAttribute.FormalSince is not null ? $", FormalSince = \"{protocolAttribute.FormalSince}\"" : string.Empty);
+			   protocolAttribute.FormalSince is not null ? $", FormalSince = \"{protocolAttribute.FormalSince}\"" : string.Empty,
+			   backwardsCompatibleCodeGeneration ? string.Empty : ", BackwardsCompatibleCodeGeneration = false"
+			   );
 
 		var sb = new StringBuilder ();
 

tests/cecil-tests/ProtocolTest.cs

@@ -30,13 +30,24 @@ namespace Cecil.Tests {
 						continue;
 					var hasProtocolAttribute = false;
 					var hasProtocolMemberAttribute = false;
+					bool? isBackwardsCompatible = null;
 					foreach (var ca in type.CustomAttributes) {
-						hasProtocolAttribute |= ca.AttributeType.Is ("Foundation", "ProtocolAttribute");
+						if (ca.AttributeType.Is ("Foundation", "ProtocolAttribute")) {
+							hasProtocolAttribute = true;
+							foreach (var prop in ca.Properties) {
+								if (prop.Name == "BackwardsCompatibleCodeGeneration") {
+									isBackwardsCompatible = (bool) prop.Argument.Value;
+									break;
+								}
+							}
+						}
 						hasProtocolMemberAttribute |= ca.AttributeType.Is ("Foundation", "ProtocolMemberAttribute");
 					}
 					if (!hasProtocolAttribute)
 						continue;
 					if (!hasProtocolMemberAttribute)
+						continue; // doesn't need to be compatible if it doesn't have any members.
+					if (isBackwardsCompatible == false)
 						continue;
 					found.Add (type.FullName);
 				}
@@ -1146,7 +1157,12 @@ namespace Cecil.Tests {
 			};
 			var unexpectedFailures = found.Except (expectedFailures);
 
-			Assert.That (unexpectedFailures, Is.Empty, $"{found.Count} new protocols found where 'BackwardsCompatibleCodeGeneration' should be set to 'false'.");
+			if (unexpectedFailures.Any ()) {
+				Console.WriteLine ("Protocols missing 'BackwardsCompatibleCodeGeneration = false':");
+				foreach (var f in unexpectedFailures.OrderBy (v => v))
+					Console.WriteLine ($"    {f}");
+			}
+			Assert.That (unexpectedFailures, Is.Empty, $"{unexpectedFailures.Count ()} new protocols found where 'BackwardsCompatibleCodeGeneration' should be set to 'false'.");
 		}
 	}
 }

tools/common/StaticRegistrar.cs

@@ -1427,6 +1427,11 @@ namespace Registrar {
 						throw ErrorHelper.CreateError (4147, Errors.MT4147, "ProtocolAttribute", type.FullName);
 					rv.FormalSinceVersion = version;
 					break;
+#if !XAMCORE_5_0
+				case "BackwardsCompatibleCodeGeneration":
+					rv.BackwardsCompatibleCodeGeneration = (bool) prop.Argument.Value;
+					break;
+#endif
 				default:
 					throw ErrorHelper.CreateError (4147, Errors.MT4147, "ProtocolAttribute", type.FullName);
 				}
@@ -5790,6 +5795,9 @@ namespace Registrar {
 		public string Name { get; set; }
 		public bool IsInformal { get; set; }
 		public Version FormalSinceVersion { get; set; }
+#if !XAMCORE_5_0
+		public bool BackwardsCompatibleCodeGeneration { get; set; }
+#endif
 	}
 
 	class BlockProxyAttribute : Attribute {