Lookup terraform binary in system path before attempting to install it

[syndicut]

When using terraform-plugin-docs in ci process it is slow and sometimes impossible to download terraform binary every time.
So I propose to first lookup terraform binary in system path and use it and fallback to downloading it.

[hashicorp-cla]

All committers have signed the CLA.

[syndicut]

@paultyng Can you have a look at this?

[paultyng]

@syndicut I no longer work at HashiCorp

[syndicut]

@syndicut I no longer work at HashiCorp

ok, sorry for bothering
can you suggest any maintainer/co-maintainer at HashiCorp?

[OJFord]

@syndicut cf. #69 (comment)

Also note https://www.hashicorp.com/blog/terraform-community-contributions.

[bflad]

Hi @syndicut 👋 Thank you for raising this and apologies for the delayed review. Using an existing Terraform CLI binary is certainly a welcome enhancement.

We recently needed to switch from the removed github.com/hashicorp/terraform-exec/tfinstall to github.com/hashicorp/hc-install. To that end, could you rebase and update this pull request (or create a new one) that uses hc-install instead? When adding the local installer, we should also update the code to fallback to installing the latest Terraform CLI version, rather than remaining hardcoded to 1.0.5.

Something like this should do the trick:

sources := []src.Source{
	&fs.AnyVersion{
		Product: &product.Terraform,
	},
	&checkpoint.LatestVersion{
		InstallDir: tmpDir,
		Product:    product.Terraform,
	},
}

installer := install.NewInstaller()
tfBin, err := installer.Ensure(context.Background(), sources)

if err != nil {
	return nil, err
}

Please reach out if you have any questions.

[bflad]

Closing, with permission, in preference of #124 👍

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