Add support for public properties defined in a private constructor

[rix0rrr]

This change is incomplete; the .NET generator doesn't know how to
deal with a private ("missing") constructor, so it throws a
NullReferenceException.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[rix0rrr]

@costleya I'm going to need your help to land this. Constructors can be private, but I think the .NET generator has been written with the assumption that every class will always have a constructor, and so it errors out trying to access it:

lerna ERR! Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object.
lerna ERR!    at Amazon.JSII.Generator.MethodExtensions.GetParametersJsonSyntaxToken(Method method) in /home/local/ANT/huijbers/Workspaces/PublicCDK/jsii/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/MethodExtensions.cs:line 47
lerna ERR!    at Amazon.JSII.Generator.Class.ClassGenerator.<CreateType>g__CreateAttributes|1_0() in /home/local/ANT/huijbers/Workspaces/PublicCDK/jsii/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/Class/ClassGenerator.cs:line 33
lerna ERR!    at Amazon.JSII.Generator.Class.ClassGenerator.CreateType() in /home/local/ANT/huijbers/Workspaces/PublicCDK/jsii/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/Class/ClassGenerator.cs:line 20
lerna ERR!    at Amazon.JSII.Generator.TypeGeneratorBase`1.CreateSyntaxTree() in /home/local/ANT/huijbers/Workspaces/PublicCDK/jsii/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/TypeGeneratorBase.cs:line 35
lerna ERR!    at Amazon.JSII.Generator.AssemblyGenerator.<>c__DisplayClass4_0.<Save>g__SaveType|3(Type type) in /home/local/ANT/huijbers/Workspaces/PublicCDK/jsii/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/AssemblyGenerator.cs:line 293
lerna ERR!    at Amazon.JSII.Generator.AssemblyGenerator.Save(String packageOutputRoot, ISymbolMap symbols, Assembly assembly, String tarballFileName, String jsiiFileName) in /home/local/ANT/huijbers/Workspaces/PublicCDK/jsii/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/AssemblyGenerator.cs:line 108
lerna ERR!    at Amazon.JSII.Generator.AssemblyGenerator.Generate(String jsiiFile, String tarballPath, ISymbolMap symbols) in /home/local/ANT/huijbers/Workspaces/PublicCDK/jsii/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/AssemblyGenerator.cs:line 59
lerna ERR!    at CommandLine.ParserResultExtensions.WithParsed[T](ParserResult`1 result, Action`1 action)
lerna ERR!    at Amazon.JSII.Generator.CLI.Program.Main(String[] args) in /home/local/ANT/huijbers/Workspaces/PublicCDK/jsii/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator.CLI/Program.cs:line 11

[rix0rrr]

Feel free to append to this PR to make it pass.

[eladb]

Can you please open two issues to add a conformance test in each language for this feature?
You can add one for Java like this one:

public void classWithPrivateConstructorAndAutomaticProperties() {
  ClassWithPrivateConstructorAndAutomaticProperties obj = new ClassWithPrivateConstructorAndAutomaticProperties();
  obj.setReadWriteString("Hello");
  assertEquals("<Some expected value>", obj.getReadOnlyString());
}

[rix0rrr]

@costleya hope it's not too much work, maybe a couple of ifs?

[costleya]

#259

@eladb This class has no public constructors, so I cannot implement a protocol test as you described. Instead, I used reflection to inspect the class and made sure it looks as expected.

[eladb]

@costleya 🤦‍♂️

[eladb]

@costleya can you push your fixes so we can merge this in and release?

[rix0rrr]

On it