From 0fe042c803840ad929b2f7733f09d8e2ee6e80e6 Mon Sep 17 00:00:00 2001
From: Tom Minka <8955276+tminka@users.noreply.github.com>
Date: Thu, 17 Dec 2020 12:50:17 +0000
Subject: [PATCH 1/4] Incorrectly using a non-generic type with type parameters
 now produces a helpful Python error instead of throwing
 NullReferenceException

---
 AUTHORS.md                  |  1 +
 CHANGELOG.md                |  1 +
 src/embed_tests/TestList.cs | 35 +++++++++++++++++++++++++++++++++++
 src/runtime/classbase.cs    |  2 +-
 src/runtime/genericutil.cs  | 15 +++++++++++----
 5 files changed, 49 insertions(+), 5 deletions(-)
 create mode 100644 src/embed_tests/TestList.cs

diff --git a/AUTHORS.md b/AUTHORS.md
index eeafd98e4..69e7b5c4a 100644
--- a/AUTHORS.md
+++ b/AUTHORS.md
@@ -60,6 +60,7 @@
 -   Sean Freitag ([@cowboygneox](https://github.com/cowboygneox))
 -   Serge Weinstock ([@sweinst](https://github.com/sweinst))
 -   Simon Mourier ([@smourier](https://github.com/smourier))
+-   Tom Minka ([@tminka](https://github.com/tminka))
 -   Viktoria Kovescses ([@vkovec](https://github.com/vkovec))
 -   Ville M. Vainio ([@vivainio](https://github.com/vivainio))
 -   Virgil Dupras ([@hsoft](https://github.com/hsoft))
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 27df6dcbe..2420d40ea 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -42,6 +42,7 @@ details about the cause of the failure
 -    Made it possible to use `__len__` also on `ICollection<>` interface objects
 -    Made it possible to call `ToString`, `GetHashCode`, and `GetType` on inteface objects
 -    Fixed objects returned by enumerating `PyObject` being disposed too soon
+-    Incorrectly using a non-generic type with type parameters now produces a helpful Python error instead of throwing NullReferenceException
 
 ### Removed
 
diff --git a/src/embed_tests/TestList.cs b/src/embed_tests/TestList.cs
new file mode 100644
index 000000000..821864372
--- /dev/null
+++ b/src/embed_tests/TestList.cs
@@ -0,0 +1,35 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Text;
+using NUnit.Framework;
+using Python.Runtime;
+
+namespace Python.EmbeddingTest
+{
+    public class TestList
+    {
+        [OneTimeSetUp]
+        public void SetUp()
+        {
+            PythonEngine.Initialize();
+        }
+
+        [OneTimeTearDown]
+        public void Dispose()
+        {
+            PythonEngine.Shutdown();
+        }
+
+        [Test]
+        public void MissingGenericTypeTest()
+        {
+            Assert.Throws<PythonException>(() =>
+            PythonEngine.Exec($@"
+from System.Collections import IList
+IList[bool]
+"));
+        }
+    }
+}
diff --git a/src/runtime/classbase.cs b/src/runtime/classbase.cs
index a62e76050..7cb6938bc 100644
--- a/src/runtime/classbase.cs
+++ b/src/runtime/classbase.cs
@@ -54,7 +54,7 @@ public virtual IntPtr type_subscript(IntPtr idx)
                 return c.pyHandle;
             }
 
-            return Exceptions.RaiseTypeError("no type matches params");
+            return Exceptions.RaiseTypeError($"{type.Namespace}.{type.Name} does not accept {types.Length} generic parameters");
         }
 
         /// <summary>
diff --git a/src/runtime/genericutil.cs b/src/runtime/genericutil.cs
index c583e64e2..7f588140c 100644
--- a/src/runtime/genericutil.cs
+++ b/src/runtime/genericutil.cs
@@ -75,20 +75,27 @@ public static List<string> GetGenericBaseNames(string ns)
         }
 
         /// <summary>
-        /// xxx
+        /// Finds a generic type with the given number of generic parameters and the same name and namespace as <paramref name="t"/>.
         /// </summary>
         public static Type GenericForType(Type t, int paramCount)
         {
             return GenericByName(t.Namespace, t.Name, paramCount);
         }
 
+        /// <summary>
+        /// Finds a generic type in the given namespace with the given name and number of generic parameters.
+        /// </summary>
         public static Type GenericByName(string ns, string name, int paramCount)
         {
-            foreach (Type t in GenericsByName(ns, name))
+            var types = GenericsByName(ns, name);
+            if (types != null)
             {
-                if (t.GetGenericArguments().Length == paramCount)
+                foreach (Type t in types)
                 {
-                    return t;
+                    if (t.GetGenericArguments().Length == paramCount)
+                    {
+                        return t;
+                    }
                 }
             }
             return null;

From 8e754b664a0461fe65a0563cf233ce2de59aeebc Mon Sep 17 00:00:00 2001
From: Tom Minka <8955276+tminka@users.noreply.github.com>
Date: Thu, 17 Dec 2020 22:10:54 +0000
Subject: [PATCH 2/4] Inlined GenericUtil.GenericsByName into GenericByName.
 Removed unused GenericUtil.GenericsForType. Other code quality improvements.

---
 src/runtime/genericutil.cs | 98 ++++++++++++++------------------------
 1 file changed, 36 insertions(+), 62 deletions(-)

diff --git a/src/runtime/genericutil.cs b/src/runtime/genericutil.cs
index 7f588140c..92b847e98 100644
--- a/src/runtime/genericutil.cs
+++ b/src/runtime/genericutil.cs
@@ -9,14 +9,13 @@ namespace Python.Runtime
     /// This class is responsible for efficiently maintaining the bits
     /// of information we need to support aliases with 'nice names'.
     /// </summary>
-    internal class GenericUtil
+    internal static class GenericUtil
     {
+        /// <summary>
+        /// Maps namespace -> generic base name -> list of generic type names
+        /// </summary>
         private static Dictionary<string, Dictionary<string, List<string>>> mapping;
 
-        private GenericUtil()
-        {
-        }
-
         public static void Reset()
         {
             mapping = new Dictionary<string, Dictionary<string, List<string>>>();
@@ -25,6 +24,7 @@ public static void Reset()
         /// <summary>
         /// Register a generic type that appears in a given namespace.
         /// </summary>
+        /// <param name="t">A generic type definition (<c>t.IsGenericTypeDefinition</c> must be true)</param>
         internal static void Register(Type t)
         {
             if (null == t.Namespace || null == t.Name)
@@ -32,22 +32,15 @@ internal static void Register(Type t)
                 return;
             }
 
-            Dictionary<string, List<string>> nsmap = null;
-            mapping.TryGetValue(t.Namespace, out nsmap);
-            if (nsmap == null)
+            Dictionary<string, List<string>> nsmap;
+            if (!mapping.TryGetValue(t.Namespace, out nsmap))
             {
                 nsmap = new Dictionary<string, List<string>>();
                 mapping[t.Namespace] = nsmap;
             }
-            string basename = t.Name;
-            int tick = basename.IndexOf("`");
-            if (tick > -1)
-            {
-                basename = basename.Substring(0, tick);
-            }
-            List<string> gnames = null;
-            nsmap.TryGetValue(basename, out gnames);
-            if (gnames == null)
+            string basename = GetBasename(t.Name);
+            List<string> gnames;
+            if (!nsmap.TryGetValue(basename, out gnames))
             {
                 gnames = new List<string>();
                 nsmap[basename] = gnames;
@@ -60,9 +53,8 @@ internal static void Register(Type t)
         /// </summary>
         public static List<string> GetGenericBaseNames(string ns)
         {
-            Dictionary<string, List<string>> nsmap = null;
-            mapping.TryGetValue(ns, out nsmap);
-            if (nsmap == null)
+            Dictionary<string, List<string>> nsmap;
+            if (!mapping.TryGetValue(ns, out nsmap))
             {
                 return null;
             }
@@ -85,61 +77,31 @@ public static Type GenericForType(Type t, int paramCount)
         /// <summary>
         /// Finds a generic type in the given namespace with the given name and number of generic parameters.
         /// </summary>
-        public static Type GenericByName(string ns, string name, int paramCount)
-        {
-            var types = GenericsByName(ns, name);
-            if (types != null)
-            {
-                foreach (Type t in types)
-                {
-                    if (t.GetGenericArguments().Length == paramCount)
-                    {
-                        return t;
-                    }
-                }
-            }
-            return null;
-        }
-
-        public static List<Type> GenericsForType(Type t)
+        public static Type GenericByName(string ns, string basename, int paramCount)
         {
-            return GenericsByName(t.Namespace, t.Name);
-        }
-
-        public static List<Type> GenericsByName(string ns, string basename)
-        {
-            Dictionary<string, List<string>> nsmap = null;
-            mapping.TryGetValue(ns, out nsmap);
-            if (nsmap == null)
+            Dictionary<string, List<string>> nsmap;
+            if (!mapping.TryGetValue(ns, out nsmap))
             {
                 return null;
             }
 
-            int tick = basename.IndexOf("`");
-            if (tick > -1)
-            {
-                basename = basename.Substring(0, tick);
-            }
-
-            List<string> names = null;
-            nsmap.TryGetValue(basename, out names);
-            if (names == null)
+            List<string> names;
+            if (!nsmap.TryGetValue(GetBasename(basename), out names))
             {
                 return null;
             }
 
-            var result = new List<Type>();
             foreach (string name in names)
             {
                 string qname = ns + "." + name;
                 Type o = AssemblyManager.LookupTypes(qname).FirstOrDefault();
-                if (o != null)
+                if (o != null && o.GetGenericArguments().Length == paramCount)
                 {
-                    result.Add(o);
+                    return o;
                 }
             }
 
-            return result;
+            return null;
         }
 
         /// <summary>
@@ -147,13 +109,12 @@ public static List<Type> GenericsByName(string ns, string basename)
         /// </summary>
         public static string GenericNameForBaseName(string ns, string name)
         {
-            Dictionary<string, List<string>> nsmap = null;
-            mapping.TryGetValue(ns, out nsmap);
-            if (nsmap == null)
+            Dictionary<string, List<string>> nsmap;
+            if (!mapping.TryGetValue(ns, out nsmap))
             {
                 return null;
             }
-            List<string> gnames = null;
+            List<string> gnames;
             nsmap.TryGetValue(name, out gnames);
             if (gnames?.Count > 0)
             {
@@ -161,5 +122,18 @@ public static string GenericNameForBaseName(string ns, string name)
             }
             return null;
         }
+
+        private static string GetBasename(string name)
+        {
+            int tick = name.IndexOf("`");
+            if (tick > -1)
+            {
+                return name.Substring(0, tick);
+            }
+            else
+            {
+                return name;
+            }
+        }
     }
 }

From 612c0ccdbed557f731669cf24e4124d8de3ed71e Mon Sep 17 00:00:00 2001
From: Tom Minka <8955276+tminka@users.noreply.github.com>
Date: Fri, 18 Dec 2020 01:29:05 +0000
Subject: [PATCH 3/4] Moved the test to Python. Added EmbeddedPythonTest with
 the capability to run any desired Python tests within NUnit.

---
 .../{TestList.cs => TestPythonTests.cs}       | 22 +++++++++++++------
 src/tests/test_generic.py                     |  5 +++++
 2 files changed, 20 insertions(+), 7 deletions(-)
 rename src/embed_tests/{TestList.cs => TestPythonTests.cs} (51%)

diff --git a/src/embed_tests/TestList.cs b/src/embed_tests/TestPythonTests.cs
similarity index 51%
rename from src/embed_tests/TestList.cs
rename to src/embed_tests/TestPythonTests.cs
index 821864372..5026cbce5 100644
--- a/src/embed_tests/TestList.cs
+++ b/src/embed_tests/TestPythonTests.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Reflection;
 using System.Text;
@@ -8,7 +9,7 @@
 
 namespace Python.EmbeddingTest
 {
-    public class TestList
+    public class TestPythonTests
     {
         [OneTimeSetUp]
         public void SetUp()
@@ -22,14 +23,21 @@ public void Dispose()
             PythonEngine.Shutdown();
         }
 
-        [Test]
-        public void MissingGenericTypeTest()
+        static IEnumerable<string[]> MyTestCases()
         {
-            Assert.Throws<PythonException>(() =>
+            yield return new[] { "test_generic", "test_missing_generic_type" };
+        }
+
+        [TestCaseSource(nameof(MyTestCases))]
+        public void EmbeddedPythonTest(string testFile, string testName)
+        {
+            string folder = @"..\\..\\..\\..\\tests";
             PythonEngine.Exec($@"
-from System.Collections import IList
-IList[bool]
-"));
+import sys
+sys.path.insert(0, '{folder}')
+from {testFile} import *
+{testName}()
+");
         }
     }
 }
diff --git a/src/tests/test_generic.py b/src/tests/test_generic.py
index c7e5a8d4d..c865ab32f 100644
--- a/src/tests/test_generic.py
+++ b/src/tests/test_generic.py
@@ -745,3 +745,8 @@ def test_nested_generic_class():
     """Check nested generic classes."""
     # TODO NotImplemented
     pass
+
+def test_missing_generic_type():
+    from System.Collections import IList
+    with pytest.raises(TypeError):
+        IList[bool]

From 20e673f42ca62df984ee148726c0e027172636a5 Mon Sep 17 00:00:00 2001
From: Tom Minka <8955276+tminka@users.noreply.github.com>
Date: Fri, 18 Dec 2020 21:05:38 +0000
Subject: [PATCH 4/4] Removed EmbeddedPythonTest

---
 src/embed_tests/TestPythonTests.cs | 43 ------------------------------
 1 file changed, 43 deletions(-)
 delete mode 100644 src/embed_tests/TestPythonTests.cs

diff --git a/src/embed_tests/TestPythonTests.cs b/src/embed_tests/TestPythonTests.cs
deleted file mode 100644
index 5026cbce5..000000000
--- a/src/embed_tests/TestPythonTests.cs
+++ /dev/null
@@ -1,43 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.IO;
-using System.Linq;
-using System.Reflection;
-using System.Text;
-using NUnit.Framework;
-using Python.Runtime;
-
-namespace Python.EmbeddingTest
-{
-    public class TestPythonTests
-    {
-        [OneTimeSetUp]
-        public void SetUp()
-        {
-            PythonEngine.Initialize();
-        }
-
-        [OneTimeTearDown]
-        public void Dispose()
-        {
-            PythonEngine.Shutdown();
-        }
-
-        static IEnumerable<string[]> MyTestCases()
-        {
-            yield return new[] { "test_generic", "test_missing_generic_type" };
-        }
-
-        [TestCaseSource(nameof(MyTestCases))]
-        public void EmbeddedPythonTest(string testFile, string testName)
-        {
-            string folder = @"..\\..\\..\\..\\tests";
-            PythonEngine.Exec($@"
-import sys
-sys.path.insert(0, '{folder}')
-from {testFile} import *
-{testName}()
-");
-        }
-    }
-}

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