Prevent unneeded fetching of Yarn version / index #202

[charlespierce]

Fixes #202

The prepare_image function was checking if the node version exists in the catalog before fetching it, however it was only checking if yarn was set on the project, not whether it had already been downloaded. This was causing the Yarn index to be re-fetched on every invocation, showing a spinner with Fetching public registry: ... before executing any command.

Updated prepare_image to also check if !catalog.yarn.contains(yarn_version), in the same way that Node is checked, before executing the fetch.

Tested locally with a project that was showing the Fetching ... spinner and verified that no spinner is shown when executing a node or yarn command.

[rwjblue]

Does this also fix the same issue with the node command? I noticed it has the same issue as yarn earlier today but didn’t have a chance to update the issue...

Whoops, sorry about that I had missed this part of the description:

Tested locally with a project that was showing the Fetching ... spinner and verified that no spinner is shown when executing a node or yarn command.

[charlespierce]

Yep, both the node and yarn shims use prepare_image to ensure that everything is downloaded so both are affected whenever a project has a yarn version set in package.json.

[mikrostew]

Nice! Thanks @charlespierce!