Very first work on trimming compatibility

[roji]

This is only a first step, more work is needed. Based on work by @NinoFloris in #3830 (thanks!)

• Annotate composite types as incompatible with trimming, while suppressing warnings for applications which don't use them.
• Create a very basic console test program for testing (Console program to verify basic flows in AOT/reflection-free mode #3820). We'll eventually run this in CI.

After this, the following issues still remain in Npgsql (for a trivial "hello world"-like program):

/home/roji/projects/npgsql/src/Npgsql/Internal/TypeHandlers/ArrayHandler.cs(258,21): Trim analysis error IL2060: Npgsql.Internal.TypeHandlers.ArrayHandler.ArrayTypeInfo<TArrayOrList>..cctor(): Call to 'System.Reflection.MethodInfo System.Reflection.MethodInfo::MakeGenericMethod(System.Type[])' can not be statically analyzed. It's not possible to guarantee the availability of requirements of the generic method. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
/home/roji/projects/npgsql/src/Npgsql/Internal/TypeHandlers/ArrayHandler.cs(246,21): Trim analysis error IL2060: Npgsql.Internal.TypeHandlers.ArrayHandler.ArrayTypeInfo<TArrayOrList>..cctor(): Call to 'System.Reflection.MethodInfo System.Reflection.MethodInfo::MakeGenericMethod(System.Type[])' can not be statically analyzed. It's not possible to guarantee the availability of requirements of the generic method. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
/home/roji/projects/npgsql/src/Npgsql/TypeMapping/ConnectorTypeMapper.cs(247,13): Trim analysis error IL2070: Npgsql.TypeMapping.ConnectorTypeMapper.GetArrayElementType(Type): 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.Interfaces' in call to 'System.Reflection.TypeInfo.ImplementedInterfaces.get'. The parameter 'type' of method 'Npgsql.TypeMapping.ConnectorTypeMapper.GetArrayElementType(Type)' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
/home/roji/projects/npgsql/src/Npgsql/Internal/TypeHandling/NullableHandler.cs(68,16): Trim analysis error IL2060: Npgsql.Internal.TypeHandling.NullableHandler.CreateDelegate<TDelegate>(Type,MethodInfo): Call to 'System.Reflection.MethodInfo System.Reflection.MethodInfo::MakeGenericMethod(System.Type[])' can not be statically analyzed. It's not possible to guarantee the availability of requirements of the generic method. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]

These are related to array/nullable handling, which currently heavily relies on reflection and is being explored by @NinoFloris (see #3813).

Apart from this the following external linker warnings are generated (especially from System.Data), not sure if the plan is to handle those in .NET 6.0:

External linker warnings

ILLink : Trim analysis error IL2026: System.Data.ColumnTypeConverter.ConvertTo(ITypeDescriptorContext,CultureInfo,Object,Type): Using method 'System.Type.GetType(String,Func<AssemblyName,Assembly>,Func<Assembly,String,Boolean,Type>,Boolean,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. The type might be removed. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.ColumnTypeConverter.ConvertTo(ITypeDescriptorContext,CultureInfo,Object,Type): Using method 'System.Type.GetType(String,Func<AssemblyName,Assembly>,Func<Assembly,String,Boolean,Type>)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. The type might be removed. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.ColumnTypeConverter.ConvertTo(ITypeDescriptorContext,CultureInfo,Object,Type): Using method 'System.Type.GetType(String)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. The type might be removed. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.ColumnTypeConverter.ConvertTo(ITypeDescriptorContext,CultureInfo,Object,Type): Using method 'System.Type.GetType(String,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. The type might be removed. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.ColumnTypeConverter.ConvertTo(ITypeDescriptorContext,CultureInfo,Object,Type): Using method 'System.Type.GetType(String,Boolean,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. The type might be removed. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.ColumnTypeConverter.ConvertTo(ITypeDescriptorContext,CultureInfo,Object,Type): Using method 'System.Type.GetType(String,Func<AssemblyName,Assembly>,Func<Assembly,String,Boolean,Type>,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. The type might be removed. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataSet.GetObjectData(SerializationInfo,StreamingContext): Using method 'System.Data.DataSet.SerializeDataSet(SerializationInfo,StreamingContext,SerializationFormat)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataSet.System.Xml.Serialization.IXmlSerializable.GetSchema(): Using method 'System.Data.XmlTreeGen.Save(DataSet,XmlWriter)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataSet.System.Xml.Serialization.IXmlSerializable.GetSchema(): Using method 'System.Data.DataSet.DataSet(SerializationInfo,StreamingContext,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataSet.System.Xml.Serialization.IXmlSerializable.GetSchema(): Using method 'System.Data.DataSet.DataSet(SerializationInfo,StreamingContext)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataSet.System.Xml.Serialization.IXmlSerializable.ReadXml(XmlReader): Using method 'System.Data.DataSet.ReadXmlSerializable(XmlReader)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataSet.System.Xml.Serialization.IXmlSerializable.WriteXml(XmlWriter): Using method 'System.Data.DataSet.WriteXml(XmlWriter,XmlWriteMode)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataSet.System.Xml.Serialization.IXmlSerializable.WriteXml(XmlWriter): Using method 'System.Data.DataSet.WriteXmlSchema(XmlWriter,SchemaFormat,Converter<Type,String>)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataTable.GetObjectData(SerializationInfo,StreamingContext): Using method 'System.Data.DataTable.SerializeDataTable(SerializationInfo,StreamingContext,Boolean,SerializationFormat)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataTable.GetSchema(): Using method 'System.Data.XmlTreeGen.Save(DataTable,XmlWriter)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataTable.ReadXml(XmlReader,XmlReadMode,Boolean): Using method 'System.Data.XmlDataLoader.LoadData(XmlReader)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataTable.ReadXml(XmlReader,XmlReadMode,Boolean): Using method 'System.Data.DataTable.ReadXmlDiffgram(XmlReader)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataTable.ReadXml(XmlReader,XmlReadMode,Boolean): Using method 'System.Data.DataTable.ReadXmlDiffgram(XmlReader)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataTable.ReadXml(XmlReader,XmlReadMode,Boolean): Using method 'System.Data.DataTable.ReadXmlSchema(XmlReader,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataTable.ReadXml(XmlReader,XmlReadMode,Boolean): Using method 'System.Data.DataTable.ReadXmlSchema(XmlReader,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataTable.WriteXmlCore(XmlWriter): Using method 'System.Data.DataTable.WriteXmlSchema(XmlWriter,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.DataTable.WriteXmlCore(XmlWriter): Using method 'System.Data.DataTable.WriteXml(XmlWriter,XmlWriteMode,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Members from serialized types may be trimmed if not referenced directly. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.Common.DbConnectionStringBuilder.GetProperties(Hashtable): Using method 'System.ComponentModel.TypeDescriptor.GetProperties(Object,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. PropertyDescriptor's PropertyType cannot be statically discovered. The Type of component cannot be statically discovered. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Data.Common.DbConnectionStringBuilder.System.ComponentModel.ICustomTypeDescriptor.GetAttributes(): Using method 'System.ComponentModel.TypeDescriptor.GetAttributes(Object,Boolean)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. The Type of component cannot be statically discovered. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Linq.Expressions.Expression.Convert(Expression,Type): Using method 'System.Linq.Expressions.Expression.Convert(Expression,Type,MethodInfo)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Creating Expressions requires unreferenced code because the members being referenced by the Expression may be trimmed. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]
ILLink : Trim analysis error IL2026: System.Text.Json.Nodes.JsonNode.System.Dynamic.IDynamicMetaObjectProvider.GetMetaObject(Expression): Using method 'System.Text.Json.Nodes.JsonNode.CreateDynamicObject(Expression,JsonNode)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Using JsonNode instances as dynamic types is not compatible with trimming. It can result in non-primitive types being serialized, which may have their members trimmed. [/home/roji/projects/npgsql/test/Npgsql.TrimmingTests/Npgsql.TrimmingTests.csproj]

Part of #3300
Part of #3820

[roji]

Will wait in case @NinoFloris has any input here (though remember it's just a first thing).