split implementations relevant to nullable metadata into extension class TypeGenericParameterExtensions

Author: smdn

src/Smdn.Reflection.ReverseGenerating/Smdn.Reflection.ReverseGenerating/Generator.cs

@@ -156,48 +156,6 @@ static bool HasUnmanagedConstraint(Type genericParameter)
         static attr => attr.AttributeType.FullName.Equals("System.Runtime.CompilerServices.IsUnmanagedAttribute", StringComparison.Ordinal)
       );
 
-    static bool IsNullableAttribute(CustomAttributeData attr)
-      => attr.AttributeType.FullName.Equals("System.Runtime.CompilerServices.NullableAttribute", StringComparison.Ordinal);
-
-    static bool IsNullableContextAttribute(CustomAttributeData attr)
-      => attr.AttributeType.FullName.Equals("System.Runtime.CompilerServices.NullableContextAttribute", StringComparison.Ordinal);
-
-    static CustomAttributeData? TryGetNullableContextAttributeFromDeclaringTypeOrOuterType(Type type)
-    {
-      Type? t = type;
-
-      for (; ; ) {
-        if ((t = t!.DeclaringType) is null)
-          return null;
-
-        var attr = t!.CustomAttributes.FirstOrDefault(IsNullableContextAttribute);
-
-        if (attr is not null)
-          return attr;
-
-        // retry against to the outer type
-        continue;
-      }
-    }
-
-    // ref: https://github.com/dotnet/roslyn/blob/main/docs/features/nullable-metadata.md#type-parameters
-    static bool HasNotNullConstraint(Type genericParameter)
-    {
-      var attrNullable = genericParameter.CustomAttributes.FirstOrDefault(IsNullableAttribute);
-      var attrNullableContext =
-        genericParameter.DeclaringMethod?.CustomAttributes?.FirstOrDefault(IsNullableContextAttribute) ??
-        TryGetNullableContextAttributeFromDeclaringTypeOrOuterType(genericParameter);
-
-      const byte notAnnotated = 1;
-
-      if (attrNullableContext is not null && notAnnotated.Equals(attrNullableContext.ConstructorArguments[0].Value))
-        // `#nullable enable` context
-        return attrNullable is null;
-      else
-        // `#nullable disable` context
-        return attrNullable is not null && notAnnotated.Equals(attrNullable.ConstructorArguments[0].Value);
-    }
-
     static bool IsValueType(Type t) => string.Equals(t.FullName, typeof(ValueType).FullName, StringComparison.Ordinal);
     static bool IsNotValueType(Type t) => !string.Equals(t.FullName, typeof(ValueType).FullName, StringComparison.Ordinal);
 
@@ -215,7 +173,7 @@ bool typeWithNamespace
 
       if (
         constraintAttrs == GenericParameterAttributes.None &&
-        HasNotNullConstraint(genericParameter)
+        genericParameter.HasGenericParameterNotNullConstraint()
       ) {
         yield return "notnull";
       }

src/Smdn.Reflection.ReverseGenerating/Smdn.Reflection/TypeGenericParameterExtensions.cs

@@ -0,0 +1,80 @@
+// SPDX-FileCopyrightText: 2022 smdn <smdn@smdn.jp>
+// SPDX-License-Identifier: MIT
+using System;
+#if NULL_STATE_STATIC_ANALYSIS_ATTRIBUTES
+using System.Diagnostics.CodeAnalysis;
+#endif
+using System.Linq;
+using System.Reflection;
+
+namespace Smdn.Reflection;
+
+internal static class TypeGenericParameterExtensions {
+  private static void ValidateGenericParameterArgument(Type param, string paramName)
+  {
+    if (param is null)
+      throw new ArgumentNullException(paramName);
+    if (!param.IsGenericParameter)
+      throw new InvalidOperationException($"{paramName} must be a generic parameter or generic argument");
+  }
+
+  // ref: https://github.com/dotnet/roslyn/blob/main/docs/features/nullable-metadata.md#type-parameters
+  public static bool HasGenericParameterNotNullConstraint(this Type genericParameter)
+  {
+    ValidateGenericParameterArgument(genericParameter, nameof(genericParameter));
+
+    var attrNullable = genericParameter.CustomAttributes.FirstOrDefault(IsNullableAttribute);
+    var attrNullableContext = FindNullableContextAttribute(genericParameter);
+
+    const byte notAnnotated = 1;
+
+    if (attrNullableContext is not null && notAnnotated.Equals(attrNullableContext.ConstructorArguments[0].Value))
+      // `#nullable enable` context
+      return attrNullable is null;
+    else
+      // `#nullable disable` context
+      return attrNullable is not null && notAnnotated.Equals(attrNullable.ConstructorArguments[0].Value);
+  }
+
+  private static bool IsNullableAttribute(CustomAttributeData attr)
+    => "System.Runtime.CompilerServices.NullableAttribute".Equals(attr.AttributeType.FullName, StringComparison.Ordinal);
+
+  private static bool IsNullableContextAttribute(CustomAttributeData attr)
+    => "System.Runtime.CompilerServices.NullableContextAttribute".Equals(attr.AttributeType.FullName, StringComparison.Ordinal);
+
+  private static bool TryGetNullableContextAttribute(
+    MemberInfo member,
+#if NULL_STATE_STATIC_ANALYSIS_ATTRIBUTES
+    [NotNullWhen(true)]
+#endif
+    out CustomAttributeData? attrNullableContext
+  )
+  {
+    attrNullableContext = member.CustomAttributes.FirstOrDefault(IsNullableContextAttribute);
+
+    return attrNullableContext is not null;
+  }
+
+  private static CustomAttributeData? FindNullableContextAttribute(Type genericParameter)
+  {
+    if (
+      genericParameter.IsGenericMethodParameter &&
+      genericParameter.DeclaringMethod is not null &&
+      TryGetNullableContextAttribute(genericParameter.DeclaringMethod, out var methodAttr)
+    ) {
+      return methodAttr;
+    }
+
+    Type? t = genericParameter;
+
+    for (; ; ) {
+      if ((t = t!.DeclaringType) is null)
+        return null;
+      if (TryGetNullableContextAttribute(t, out var typeAttr))
+        return typeAttr;
+
+      // retry against to the outer type
+      continue;
+    }
+  }
+}