extraDirectories property should validate if the supplied path exists

Environment:

• Jib version: 3.1.4
• Build tool: Maven 3.6.2

Description of the issue:

<configuration>
    <extraDirectories>
         <paths>
             <path>missing/folder</path>
          </paths>
     </extraDirectories>
</configuration>

Using the extraDirectories config above to copy additional files doesn’t fail the build even the path is invalid or not a folder. This behaviour is not good for catching bugs early if the additional files are crucial for the docker container.

Expected behaviour: Should be similar to the docker build command which would throw the following exception if a Dockerfile has a command to copy a non-existent folder:

 => ERROR [stage-1 2/2] COPY missing/folder /app                                                                                                                                     0.0s
------
 > [stage-1 2/2] COPY missing/folder /app:
------
failed to compute cache key: "/missing/folder" not found: not found

[chanseokoh]

The reason we don’t check the existence is due to the default implicit directory src/main/jib, which doesn’t exist often. Perhaps we should fail only for non-default directories. Contributions are welcome.

[meltsufin]

Thank you for submitting this enhancement request.