Use configuration as the primary source for module.calls

[radeksimko]

Depends on #722

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Background

We have recently introduced a custom command module.calls which currently exclusively uses the data from the .terraform folder. There is currently no other easy way of getting the important metadata, such as (1) module hierarchy, (2) installed location on disk, (3) installed version.

As described in hashicorp/terraform#30005 the existing behaviour of Terraform CLI is that old (removed) modules are kept in the filesystem "cache" and so using it as the only source leads to suboptimal behaviour of showing stale providers which are never removed unless the user explicitly removes them manually.

Use-cases

Provide more accurate representation of "module calls" for a given module URI in module.calls response.

Attempted Solutions

Stale modules returned from disk cache.

Proposal

• module metadata: Decode module calls (for uninitialized modules) #882
• Update module.calls custom command to use this metadata as a primary source and module manifest as secondary (manifest can provide hierarchy which we can't infer from the config)
• Update relevant documentation

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