JavaMavenWorkflow sam build fails with `[Errno 20] Not a directory`

Start with the JavaMavenWorkflow and its CopySource step, then inspect the copytree call shown in the traceback. Reproduce sam build --debug with CodeUri pointing to lambdas/mainlambda/target/lambda.jar and compare it with the expected Maven reactor command. Done means the existing project builds the JAR without the NotADirectoryError.

Getting an error when running sam build in an existing project of mine,
where the sam template has a CodeUri that points to a JAR file in a reactor build submodule.

Steps to reproduce the issue:

1. existing java maven project using reactor builds with
   1.1 a shaded jar generated in a maven submodule's target directory
   (<project-top-level>/lambdas/mainlambda/target/lambda.jar in my case)
   1.2 a template.yaml in the <project-top-level> directory using
   CodeUri: lambdas/mainlambda/target/lambda.jar
2. cd <project-top-level>
3. sam build --debug

Observed result:

2019-04-28 19:31:55 Collected default values for parameters: {}
2019-04-28 19:31:55 12 resources found in the template
2019-04-28 19:31:55 Found Serverless function with name='LatestFunction' and CodeUri='lambdas/mainlambda/target/lambda.jar'
2019-04-28 19:31:55 Found Serverless function with name='LiveFunction' and CodeUri='lambdas/mainlambda/target/lambda.jar'
2019-04-28 19:31:55 Found Serverless function with name='TestRunnerFunction' and CodeUri='lambdas/testlambda/target/lambda.jar'
2019-04-28 19:31:55 Building resource 'LatestFunction'
2019-04-28 19:31:55 Looking for a supported build workflow in following directories: ['<scrubbed>/GitRepos/someproject/lambdas/mainlambda/target/lambda.jar', '<scrubbed>/GitRepos/someproject']
2019-04-28 19:31:55 Loading workflow module 'aws_lambda_builders.workflows'
2019-04-28 19:31:55 Registering workflow 'PythonPipBuilder' with capability 'Capability(language='python', dependency_manager='pip', application_framework=None)'
2019-04-28 19:31:55 Registering workflow 'NodejsNpmBuilder' with capability 'Capability(language='nodejs', dependency_manager='npm', application_framework=None)'
2019-04-28 19:31:55 Registering workflow 'RubyBundlerBuilder' with capability 'Capability(language='ruby', dependency_manager='bundler', application_framework=None)'
2019-04-28 19:31:55 Registering workflow 'GoDepBuilder' with capability 'Capability(language='go', dependency_manager='dep', application_framework=None)'
2019-04-28 19:31:55 Registering workflow 'GoModulesBuilder' with capability 'Capability(language='go', dependency_manager='modules', application_framework=None)'
2019-04-28 19:31:55 Registering workflow 'JavaGradleWorkflow' with capability 'Capability(language='java', dependency_manager='gradle', application_framework=None)'
2019-04-28 19:31:55 Registering workflow 'JavaMavenWorkflow' with capability 'Capability(language='java', dependency_manager='maven', application_framework=None)'
2019-04-28 19:31:55 Registering workflow 'DotnetCliPackageBuilder' with capability 'Capability(language='dotnet', dependency_manager='cli-package', application_framework=None)'
2019-04-28 19:31:55 Found workflow 'JavaMavenWorkflow' to support capabilities 'Capability(language='java', dependency_manager='maven', application_framework=None)'
2019-04-28 19:31:55 Running workflow 'JavaMavenWorkflow'
2019-04-28 19:31:55 Running JavaMavenWorkflow:CopySource
2019-04-28 19:31:55 JavaMavenWorkflow:CopySource raised unhandled exception
Traceback (most recent call last):
  File "<scrubbed>/.virtualenvs/aws/lib/python3.6/site-packages/aws_lambda_builders/workflow.py", line 248, in run
    action.execute()
  File "<scrubbed>/.virtualenvs/aws/lib/python3.6/site-packages/aws_lambda_builders/actions.py", line 101, in execute
    copytree(self.source_dir, self.dest_dir, ignore=shutil.ignore_patterns(*self.excludes))
  File "<scrubbed>/.virtualenvs/aws/lib/python3.6/site-packages/aws_lambda_builders/utils.py", line 43, in copytree
    names = os.listdir(source)
NotADirectoryError: [Errno 20] Not a directory: '<scrubbed>/GitRepos/someproject/lambdas/mainlambda/target/lambda.jar'

Expected result:

I would expect it to run the equivalent of

(in <project-top-level> folder)
mvn package -Dmaven.test.skip=true -pl lambdas/mainlambda -am

Which is what i run when I want to just build lambda.jar

• -pl lambdas/mainlambda because that is the module folder of the target folder where lambda.jar is located.
• -am because otherwise reactor builds will fail
• -Dmaven.test.skip=true because when run from the aws-toolkit, you don't want to rerun the whole test suite (?)

This sam build failure is preventing me from creating launch configurations using aws-toolkit for Intellij.

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

I don't believe my environment makes any difference in this issue, but I'll answer any request for more information if that is deemed necessary