Write jnigen_maven_downloads.json to maven directories, and only rerun maven when required.

[mahesh-hegde]

maven commands take significant time in tests. So why not

• write a maven_downloads.json file to download folder containing last download config.
• Check the file before invoking maven.
• invoke maven command only if dependencies are changed.

[mahesh-hegde]

To be more elaborate, maven doesn't re-download from the internet every time. It has a local cache in ~/.m2 . However, invoking maven itself is a source of slowness.

Possible design:

maven_downloads.json

{
    "comment": "This file avoids the need to invoke maven every time, which can be slow. Delete this file to force refresh"
    "downloaded_on": "date"
    "source_deps": [""]
    "jar_deps": [""]
}

TODO: Invalidation

Re-download is triggered when:

conservative caching:

• Any file in the directory is older than jnigen.yaml

aggressive caching:

• Compare maven_downloads spec by content. If any dependency is changed

Other criteria to invalidate: (can be used in conjunction)

• stale downloads: If downloads are older than a predefined timeout

• anomalies: JSON file older than any of the downloads.

TODO: Manual invalidation

• by CLI-only flag --force-invoke-maven

or

• disable caching in YAML, which can be overridden by CLI as well.

[mahesh-hegde]

cc: @dcharkes

[HosseinYousefi]

I think there is a case to be made to completely remove maven support from jnigen's main workflow. We might instead add some helper scripts like dart run jnigen:maven_init that create the intial pom.xml files in the directory.

Closing this.