For normal provider installation we want to associate each provider with
a selected version number and find a suitable package for that version
that conforms to the official hashes for that release.
Those requirements are very onerous for a provider developer currently
testing a not-yet-released build, though. To allow for that case this new
CLI configuration feature allows overriding specific providers to refer
to give local filesystem directories.
Any provider overridden in this way is not subject to the usual
restrictions about selected versions or checksum conformance, and
activating an override won't cause any changes to the selections recorded
in the lock file because it's intended to be a temporary setting for one
developer only.
This is, in a sense, a spiritual successor of an old capability we had to
override specific plugins in the CLI configuration file. There were
some vestiges of that left in the main package and CLI config package
but nothing has actually been honoring them for several versions now and
so this commit removes them to avoid confusion with the new mechanism.
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