The CLI config can be written in both native HCL and HCL JSON syntaxes, so
the provider_installation block must be expressible using JSON too. Our
previous checks to approximate HCL 2-level strictness were too strict for
HCL JSON where things are more ambiguous even in HCL 2, so this includes
some additional relaxations if we detect that we're decoding an AST
produced from a JSON file.
This is still subject to the quirky ways HCL 1 handles JSON though, so
the JSON value must be structured in a way that doesn't trigger HCL's
heuristics that try to guess what is a block and what is an attribute.
(This is the issue that HCL 2 fixes by always decoding using a schema;
there's more context on this in:
https://log.martinatkins.me/2019/04/25/hcl-json/ )
Unfortunately in the user model the noun "source" is already used for the
argument in the required_providers block to specify which provider to use,
so it's confusing to use the same noun to also refer to the method used to
obtain that provider.
In the hope of mitigating that confusion, here we use the noun "method",
as in "installation method", to talk about the decision between getting
a provider directly from its origin registry or getting it from some
mirror. This is distinct from the provider's "source", which is the
location where a provider _originates_ (prior to mirroring).
This noun is also not super awesome, but better than overloading an
existing term in the same feature.
An earlier commit added a redundant stub for a new network mirror source
that was already previously stubbed as HTTPMirrorSource.
This commit removes the unnecessary extra stub and changes the CLI config
handling to use it instead. Along the way this also switches to using a
full base URL rather than just a hostname for the mirror, because using
the usual "Terraform-native service discovery" protocol here doesn't isn't
as useful as in the places we normally use it (the mirror mechanism is
already serving as an indirection over the registry protocol) and using
a direct base URL will make it easier to deploy an HTTP mirror under
a path prefix on an existing static file server.
This new CLI config block type allows explicitly specifying where
Terraform should look to find provider plugins for installation. This is
not used anywhere as of this commit, but in a future commit we'll change
package main to treat the presence of a block of this type as a request
to disable the default set of provider sources and use these explicitly-
specified ones instead.
Martin Atkins