Strip flags from internal_plugin args (fixes TF_CLI_ARGS usage)

[aars]

This fixes #14847, #17094

Hi,

This PR fixes the internal plugins breaking over the amount of args received. Though it might be a bit naïve.

My first approach was to add an exception to mergeEnvArgs, to simply skip the merge if the command was internal-plugin. Something something, separation of concerns, so I decided to let the internal plugin command handle this. I think the cli package guarantees that all command options/flags are prefixed with a dash, making it easy and reliable to filter these.

I added a unit test for the newly added function. I couldn't find any test that actually called the Run function, but I might have overlooked something.

[aars]

Any input on this?

[lorengordon]

Just ran into this problem. Would be nice to get a fix.

[apparentlymart]

Thanks for working on this, @aars!

I follow and agree with your rationale for doing this as a post-processing step within the command itself, since this is a concern rather specific to this command, and the execution of it is totally under Terraform's control anyway so we can be sure that arguments starting with - cannot be a legitimate part of the interface of this command.

There are other commands that don't support -var-file etc too which would still be subject to the problem, and that's why we also offer the command-specific variants of TF_CLI_ARGS like TF_CLI_ARGS_plan, but addressing this for internal-plugin specifically does at least ensure that the main Terraform workflow commands can work successfully with the general TF_CLI_ARGS set.

Thanks again!

[ghost]

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