Skipping an optional property in an abstract class generates invalid C# code

[skinny85]

🐛 Bug Report

Affected Languages

• TypeScript or Javascript
• Python
• Java
• .NET (C#, F#, ...)

General Information

• JSII Version: 1.12.0
• Platform: Darwin 186590cdb71d.ant.amazon.com 18.7.0 Darwin Kernel Version 18.7.0: Thu Jun 18 20:50:10 PDT 2020; root:xnu-4903.278.43~1/RELEASE_X86_64 x86_64

What is the problem?

The following CDK PR: aws/aws-cdk#10488 broke C# compilation:

#STDOUT> Amazon/CDK/AWS/RDS/DatabaseClusterBaseProxy.cs(86,60): error CS0115: 'DatabaseClusterBaseProxy.Engine': no suitable method found to override [/tmp/npm-pack8yL6Iq/Amazon.CDK.MonoCDK.Experiment/Amazon.CDK.MonoCDK.Experiment.csproj]
#STDOUT> Amazon/CDK/AWS/RDS/DatabaseInstanceBaseProxy.cs(88,61): error CS0115: 'DatabaseInstanceBaseProxy.Engine': no suitable method found to override [/tmp/npm-pack8yL6Iq/Amazon.CDK.MonoCDK.Experiment/Amazon.CDK.MonoCDK.Experiment.csproj]
#STDOUT> Amazon/CDK/AWS/RDS/DatabaseClusterBaseProxy.cs(86,60): error CS0115: 'DatabaseClusterBaseProxy.Engine': no suitable method found to override [/tmp/npm-pack8yL6Iq/Amazon.CDK.AWS.RDS/Amazon.CDK.AWS.RDS.csproj]
#STDOUT> Amazon/CDK/AWS/RDS/DatabaseInstanceBaseProxy.cs(88,61): error CS0115: 'DatabaseInstanceBaseProxy.Engine': no suitable method found to override [/tmp/npm-pack8yL6Iq/Amazon.CDK.AWS.RDS/Amazon.CDK.AWS.RDS.csproj]

The code is roughly:

interface ISomeInterface {
  readonly optProp?: string;

  // just to make it clear this is not a struct
  bind(options: string): string;
}

abstract class SomeBase implements ISomeInterface {
  public bind(options: string): string { return options; }
}

export class Some extends SomeBase {
  public readonly optProp = 'Some';
}

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