Variables that are unset return the correct diagnostic but throw a panic when
we later parse the job body. Return early if there are any variable parsing
errors instead of continuing in a potentially invalid state.
Allow expressing `meta` and `env` blocks as map attributes as well.
`env` and `meta` should support arbitrary key and values, yet hcl2
restricts the keys to valid identifiers. For example, block attribute
identifiers may not contain dots, `.`, which frequently used in meta
fields, and sometimes in environment variable fields.
This change attempts to parse `env`/`meta` both as an attribute and as a
block.
This additionally allows better expressivity for env/meta blocks, using
functions. For example, one can reuse a set of environment variables for
multiple tasks, using a local common_envs value:
```hcl
env = merge(local.common_envs, {"more_env_key", "..."})
```
The HCL2 parser needs to apply special parsing tweaks so it can parse
the task config the same way as HCL1. Particularly, it needs to
reinterprets `map[string]interface{}` fields and blocks that appear when
attributes are expected.
This commit restricts the special casing to the Job fields, and ignore
`variables` and `locals` block.
Tim Gross