Gradle project static HTML doesn't get generated

Description

Given a Gradle project with the following 2 tasks (one generating server code with language spring and the other one the static HTML with language html2). The problem is that nothing gets written in the case of the static HTML task when running the build task. If generate HTML task gets called explicitly it works fine.

Swagger-codegen version

io.swagger:swagger-annotations:1.5.16
io.swagger:swagger-codegen:2.2.3

Swagger declaration file content or url

def generateServerCodeTask(name, swaggerInputFile, swaggerOutputDir, apiPackage, modelPackage) {
  return tasks.create("${name}GenerateServerCode") {

    doFirst {
      io.swagger.parser.SwaggerParser parser = new io.swagger.parser.SwaggerParser()
      io.swagger.parser.util.SwaggerDeserializationResult result = parser.readWithInfo(swaggerInputFile, null, true)
      if (!result.messages.isEmpty()) {
        System.err.println("Swagger validation: " + result.messages.stream().collect(java.util.stream.Collectors.joining("\n")))
      }
    }

    doLast {
      def config = new io.swagger.codegen.config.CodegenConfigurator()
      config.inputSpec = swaggerInputFile
      config.outputDir = swaggerOutputDir
      config.lang = 'spring'
      config.templateDir = "${rootProject.rootDir}/swagger/templates/server/"
      config.apiPackage = apiPackage
      config.modelPackage = modelPackage
      config.modelNameSuffix = "WS"
      config.additionalProperties = [
        "dateLibrary"      : "java8",
        "interfaceOnly"    : true,
        "useBeanValidation": true
      ]
      config.skipOverwrite = false
      config.addSystemProperty("models", "")
      config.addSystemProperty("apis", "")
      config.addSystemProperty("apiTests", "false")
      config.addSystemProperty("apiDocs", "false")
      config.addSystemProperty("modelDocs", "false")
      config.addSystemProperty("modelTests", "false")

      new io.swagger.codegen.DefaultGenerator().opts(config.toClientOptInput()).generate()
    }
  }
}


def generateServerHtmlDocTask(name, swaggerInputFile, htmlDocOutputDir) {
  return tasks.create("${name}GenerateHtmlDoc") {

    doFirst {
      io.swagger.parser.SwaggerParser parser = new io.swagger.parser.SwaggerParser()
      io.swagger.parser.util.SwaggerDeserializationResult result = parser.readWithInfo(swaggerInputFile, null, true)
      if (!result.messages.isEmpty()) {
        System.err.println("Swagger validation: " + result.messages.stream().collect(java.util.stream.Collectors.joining("\n")))
      }
    }
    
    doLast {
      def config = new io.swagger.codegen.config.CodegenConfigurator()
      config.inputSpec = swaggerInputFile
      config.outputDir = htmlDocOutputDir
      config.lang = 'html2'

      new io.swagger.codegen.DefaultGenerator().opts(config.toClientOptInput()).generate()
    }
  }
}

Attaching both tasks to compileJava.

compileJava {
    dependsOn parent.generateServerHtmlDocTask(project.name, "${projectDir}/swagger/api-spec.yml", "${buildDir}/docs"), parent.generateServerCodeTask(project.name, "${projectDir}/swagger/api-spec.yml", "${buildDir}/swagger-code", "com.company.api", "com.company.api.dto")
}

Command line used for generation

./gradlew clean build

Steps to reproduce

1. Setup a multi-module Gradle project with java and spring boot plugins
2. include the 2 tasks and an arbitrary YAML input file
3. run ./gradlew clean build

Suggest a fix/enhancement

Start with the compileJava dependency and the two task closures shown in the issue, then inspect the DefaultGenerator().opts(...).generate() entry point for differences between build execution and explicit task execution. Done means ./gradlew clean build generates the html2 output in build/docs as well as the server output.