Improve UX for async edge cases

[radeksimko]

Once #195 & #219 is resolved it's likely that a number of edge cases will emerge.

Error messages may not be as helpful as we'd like them to be and the UX overall may need some enhancements, but it's not clear yet how to best address all these edge cases, so I'm creating this issue to track it and brain dump some known unknowns.

When we add a new root module, we always discover module manifest and plugin lock file locations, just so they can be tracked by the watcher.

There is however a number of operations which run asynchronously after adding the module roughly in the following order

1. parsing module manifest
2. discovering terraform executor
3. obtaining terraform version
4. finding compatible language parser (there's just one for now, but it's gated on 0.12+)
5. obtaining schema (to be gated on version too as per Support provider aliases and 0.13 identities #164)

Any of the above can either be in progress of loading - i.e. not done yet when the user is e.g.

• requesting completion
• requesting formatting

or any of these can fail, which makes any functionality depending on it to error out, e.g.

• unreadable module manifest
• no terraform found in $PATH
• no terraform version found (e.g. because of tfenv unparseable output, or binary being un-executable)
• no compatible parser found (e.g. because of too old TF version)
• no compatible schema storage found (e.g. because of TF 0.11 and older)
• failed to obtain schema (e.g. because of missing backend auth, invalid config or other reasons)

The question is how should these edge cases be communicated, if at all to the user and when.

There was an attempt to surface some of this in #187 but surfacing TF errors will generally require some better handling. Also we should aim to keep the messaging relevant in time or per event (see #212)

[radeksimko]

As discussed with @paultyng we can just silently log most of these errors for now, as opposed to showing any notifications.

The easiest way to do this would probably be just logging a summary of errors after finishing the load of each module here:

terraform-ls/internal/terraform/rootmodule/root_module.go

Lines 198 to 199 in fe3b6a0

	return errs.ErrorOrNil()

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.
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