[generator] (class-parse regression) mark obfuscated types in generator.

Basically this is part of the problems reported at
https://bugzilla.xamarin.com/show_bug.cgi?id=44263

In good old `jar2xml` era, we marked "obfuscated" types at jar2xml so
that those types are not generated in the API XML.

class-parse is not that clever and generates everything as is.

We could make changes to api-xml-adjuster, but instead of doing the same
as jar2xml, we had better bring in flexibility to obfuscation marking.
That is -

	- If there is `obfuscated='false'` attribute specification by
	  API metadata fixup, then do not mark as obfuscated in any case.
	- If not, process any lowercase-named types and nested types
	  as obfuscated, such as 'a', 'SomeType$a', or 'SomeType$b$a'.

We had been seeing some obfuscated types like `b$a` as NOT marked as
obfuscated in the past, because we were checking only a,aa,aaa,aaaa and
aaaaa as the parent type for nested types. That should be fixed.

Due to code structures, we cannot take the same code path as jar2xml
(we don't hold list of sibling classes when processing an XML element).
https://github.com/xamarin/jar2xml/blob/master/JavaPackage.java#L78

To fix this issue, we process marking as part of StripNonBindables().

Fixing bug #44263 then exposed another problem; StripNonBindables()
was not complete and it was not processing nested C# types at all.
Thus we had generated non-bindable code before. This change fixes this
issue at the same time, for fixing the bug.

Thus, this will result in "API breakage" looking changes in the end,
but the bindings were invalid and should be removed without
compatibility concern.

Author: atsushieno

tools/generator/CodeGenerator.cs

@@ -304,6 +304,7 @@ static void Run (CodeGeneratorOptions options, DirectoryAssemblyResolver resolve
 			if (gens == null) {
 				return;
 			}
+			gens = gens.Where (g => !g.IsObfuscated && g.Visibility != "private").ToList ();
 			apiSource = p.ApiSource;
 			opt.Gens = gens;
 

tools/generator/GenBase.cs

@@ -53,6 +53,10 @@ public bool IsDeprecated {
 			get { return support.IsDeprecated; }
 		}
 
+		public bool IsObfuscated {
+			get { return support.IsObfuscated; }
+		}
+
 		public string DeprecatedComment {
 			get { return support.DeprecatedComment; }
 		}
@@ -718,6 +722,9 @@ public void StripNonBindables ()
 			// have to "implement" those methods because they are declared and you have to implement
 			// any declared methods in C#. That is going to be problematic a lot.
 			methods = methods.Where (m => !m.IsInterfaceDefaultMethod).ToList ();
+			nested_types = nested_types.Where (n => !n.IsObfuscated).ToList ();
+			foreach (var n in nested_types)
+				n.StripNonBindables ();
 		}
 
 		public void FillProperties ()

tools/generator/GenBaseSupport.cs

@@ -18,6 +18,7 @@ public abstract class GenBaseSupport
 		public abstract string DeprecatedComment { get; }
 		public abstract bool IsGeneratable { get; }
 		public abstract bool IsGeneric { get; }
+		public abstract bool IsObfuscated { get; }
 		public abstract string FullName { get; set; }
 		public abstract string Name { get; set; }
 		public abstract string Namespace { get; }
@@ -92,6 +93,10 @@ public override bool IsAcw {
 		public override bool IsDeprecated {
 			get { return deprecated; }
 		}
+
+		public override bool IsObfuscated {
+			get { return false; } // obfuscated types have no chance to be already bound in managed types.
+		}
 
 		public override string DeprecatedComment {
 			get { return deprecatedComment; }
@@ -198,8 +203,8 @@ public XmlGenBaseSupport (XmlElement pkg, XmlElement elem)
 				name = TypeNamePrefix + raw_name;
 				full_name = String.Format ("{0}.{1}{2}", ns, idx > 0 ? StringRocks.TypeToPascalCase (java_name.Substring (0, idx + 1)) : String.Empty, name);
 			}
-			//marshaler = elem.XGetAttribute ("marshaler");
-			//if (!string.IsNullOrEmpty (marshaler)) throw new Exception ();
+
+			obfuscated = IsObfuscatedName (java_name) && elem.XGetAttribute ("obfuscated") != "false";
 		}
 
 		public override bool IsAcw {
@@ -219,6 +224,11 @@ public override string DeprecatedComment {
 		public override bool IsGeneratable {
 			get { return true; }
 		}
+
+		bool obfuscated;
+		public override bool IsObfuscated {
+			get { return obfuscated; }
+		}
 
 		string java_name;
 		public override string JavaSimpleName {
@@ -291,6 +301,17 @@ public override bool ValidateNamespace ()
 			}
 			return true;
 		}
+
+		bool IsObfuscatedName (String name)
+		{
+			if (name.StartsWith ("R.", StringComparison.Ordinal))
+				return false;
+			int idx = name.LastIndexOf ('.');
+			string last = idx < 0 ? name : name.Substring (idx + 1);
+			if (last.Any (c => (c < 'a' || 'z' < c) && (c < '0' || '9' < c)))
+					return false;
+			return true;
+		}
 	}
 
 	public class InterfaceXmlGenBaseSupport : XmlGenBaseSupport