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/ )
Martin Atkins