The `SourceDestCheck` attribute can only be changed via
`ModifyInstance`, so the AWS instance resource's `Create` function calls
out to `Update` before it returns to take care of applying
`source_dest_check` properly.
The `Update` function originally guarded against unnecessary API calls
with `GetOk`, which worked fine until #993 when we changed the `GetOk`
semantics to no longer distinguish between "configured and zero-value"
and "not configured".
I attempted in #1003 to fix this by switching to `HasChange` for the
guard, but this does not work in the `Create` case.
I played around with a few different ideas, none of which worked:
(a) Setting `Default: true` on `source_dest_check' has no effect
(b) Setting `Computed: true` on `source_dest_check' and adding a `d.Set`
call in the `Read` function (which will initially set the value to `true`
after instance creation). I really thought I could get this to work,
but it results in the following:
```go
d.Get('source_dest_check') // true
d.HasChange('source_dest_check') // false
d.GetChange('source_dest_check') // old: false, new: false
```
I couldn't figure out a way of coherently dealing with that result, so I
ended up throwing up my hands and giving up on the guard altogether.
We'll call `ModifyInstance` more than we have to, but this at least
yields expected behavior for both Creates and Updates.
Fixes#1020
/cc @sethvargo
This was causing a race with whichever provider was configured first
would "win" the configuration slot. We need to make sure to append the
unique provider name to the end of the key.
Note: this doesn't have tests. We don't test this yet. :(
/cc @sethvargo
Prior to this commit, we'd only persist the result of calling Input if
any input was given (len(result) > 0). The result was that every module
would also repeat asking for input even if there was no input to be
asked for.
This commit makes it so that if no input was received, we still set a
sentinel so that modules don't re-ask.
