Fixes#4789
This improves the validation that valid provider aliases are used.
Previously, we required that provider aliases be defined in every module
they're used. This isn't correct because the alias may be used in a
parent module and inherited.
This removes that validation and creates the validation that a provider
alias must be defined in the used module or _any parent_. This allows
inheritance to work properly.
We've always had this type of validation for aliases because we believe
its a good UX tradeoff: typo-ing an alias is really painful, so we
require declaration of alias usage. It may add a small burden to
declare, but since relatively few aliases are used, it improves the
scenario where a user fat-fingers an alias name.
This changes the key for the storage to be the _raw_ source from the
module, not the fully expanded source. Example: it'll be a relative path
instead of an absolute path.
This allows the ".terraform/modules" directory to be portable when
moving to other machines. This was a behavior that existed in <= 0.7.2
and was broken with #8398. This amends that and adds a test to verify.
Mitchell Hashimoto