[generator] Improve generic type lookup (#552)

Fixes: #543

In commit 262743b we began stripping the arity from Cecil imported
types so that we wouldn't write invalid types like
``System.Collections.Generic.IList`1<string>``, in order to correctly
emit `System.Collections.Generic.IList<string>`.

However when we try to resolve these types in the `SymbolTable` we
only look at the type name, ignoring the generic type parameters.  In
this case we are looking for `System.Collections.Generic.IList` but
the type is stored in the symbol table with the arity to disambiguate
types like ``Action`1`` and ``Action`2``.  Therefore our lookup fails
because the table key is ``System.Collections.Generic.IList`1``.

For example, if we have `LibraryA.dll` with:

	public class Foo : Java.Lang.Object {
	    public virtual void Bar (IList<string> p0) {…}
	}

And we attempt to bind a `LibraryB.jar` which references
`LibraryA.dll`, overriding `Foo.Bar()`:

	public class Foo2 : Foo {
	    public override void Bar (IList<string> p0) {…}
	}

Then `Foo2.Bar()` would elicit a BG8800 warning:

	warning BG8800: Unknown parameter type System.Collections.Generic.IList<System.String> in method Bar in managed type Foo2.

Fix type lookup so that if the type is not found in the `SymbolTable`
and there are generic type parameters, calculate the arity from the
generic type parameters and look in the table again.

That is, `System.Collections.Generic.IList<string>` is rechecked as
``System.Collections.Generic.IList`1``, which allows the type to be
found.

Author: jpobst

tools/generator/Java.Interop.Tools.Generator.ObjectModel/Symbols/SymbolTable.cs

@@ -260,7 +260,15 @@ public ISymbol Lookup (string java_type)
 					if (all_symbols_cache == null)
 						all_symbols_cache = new ConcurrentDictionary<string, ISymbol> (symbols.Values.SelectMany (v => v).GroupBy (s => s.FullName).ToDictionary (s => s.Key, s => s.FirstOrDefault ()));
 
-					all_symbols_cache.TryGetValue (key, out sym);
+					if (!all_symbols_cache.TryGetValue (key, out sym)) {
+						// We may be looking for a type like:
+						// - System.Collections.Generic.IList<Java.Util.Locale.LanguageRange>
+						// Our key is "System.Collections.Generic.IList", but it's stored in
+						// the symbol table with the arity so we need to look for
+						// "System.Collections.Generic.IList`1" to find a match
+						key = AddArity (key, type_params);
+						all_symbols_cache.TryGetValue (key, out sym);
+					}
 				}
 			}
 			ISymbol result;
@@ -290,7 +298,32 @@ public ISymbol Lookup (string java_type)
 
 			return result;
 		}
-		
+
+		private string AddArity (string key, string typeParams)
+		{
+			if (string.IsNullOrWhiteSpace (typeParams) || !typeParams.StartsWith ("<") || !typeParams.EndsWith (">"))
+				return key;
+
+			var nested_count = 0;
+			var arity = 1;
+
+			// Remove the outer <>
+			typeParams = typeParams.Substring (1, typeParams.Length - 2);
+
+			foreach (var c in typeParams) {
+				if (c == '>')
+					nested_count--;
+
+				if (c == '<')
+					nested_count++;
+
+				if (nested_count == 0 && c == ',')
+					arity++;
+			}
+
+			return $"{key}`{arity}";
+		}
+
 		public void Dump ()
 		{
 			foreach (var p in symbols) {

tools/generator/Tests/Unit-Tests/SymbolTableTests.cs

@@ -0,0 +1,40 @@
+using System;
+using MonoDroid.Generation;
+using NUnit.Framework;
+
+namespace generatortests
+{
+	[TestFixture]
+	public class SymbolTableTests
+	{
+		[Test]
+		public void FindGenericTypes ()
+		{
+			var table = new SymbolTable ();
+
+			var list = new InterfaceGen (new GenBaseSupport {
+				Name = "System.Collections.Generic.IList`1",
+				FullName = "System.Collections.Generic.IList`1",
+				JavaSimpleName = "System.Collections.Generic.IList`1"
+			});
+
+			table.AddType (list);
+
+			var dict = new InterfaceGen (new GenBaseSupport {
+				Name = "System.Collections.Generic.IDictionary`2",
+				FullName = "System.Collections.Generic.IDictionary`2",
+				JavaSimpleName = "System.Collections.Generic.IDictionary`2"
+			});
+
+			table.AddType (dict);
+
+			Assert.AreEqual ("System.Collections.Generic.IList`1", table.Lookup ("System.Collections.Generic.IList<Java.Util.Locale.LanguageRange>").FullName);
+			Assert.AreEqual ("System.Collections.Generic.IList`1", table.Lookup ("System.Collections.Generic.IList<List<Java.Util.Locale.LanguageRange>>").FullName);
+
+			Assert.AreEqual ("System.Collections.Generic.IDictionary`2", table.Lookup ("System.Collections.Generic.IDictionary<string, Java.Util.Locale.LanguageRange>").FullName);
+			Assert.AreEqual ("System.Collections.Generic.IDictionary`2", table.Lookup ("System.Collections.Generic.IDictionary<string, List<Java.Util.Locale.LanguageRange>>").FullName);
+
+			Assert.AreEqual ("System.Collections.Generic.IList`1", table.Lookup ("System.Collections.Generic.IList<Dictionary<string, Java.Util.Locale.LanguageRange>>").FullName);
+		}
+	}
+}