This introduces an `ErrorMessage` newtype which wraps `Text` in a manner which is designed to be easy to construct, and difficult to deconstruct.
It provides functionality similar to `Data.Text.Extended`, but designed _only_ for error messages. Error messages are constructed through `fromString`, concatenation, or the `toErrorValue` function, which is designed to be overridden for all meaningful domain types that might show up in an error message. Notably, there are not and should never be instances of `ToErrorValue` for `String`, `Text`, `Int`, etc. This is so that we correctly represent the value in a way that is specific to its type. For example, all `Name` values (from the _graphql-parser-hs_ library) are single-quoted now; no exceptions.
I have mostly had to add `instance ToErrorValue` for various backend types (and also add newtypes where necessary). Some of these are not strictly necessary for this changeset, as I had bigger aspirations when I started. These aspirations have been tempered by trying and failing twice.
As such, in this changeset, I have started by introducing this type to the `parseError` and `parseErrorWith` functions. In the future, I would like to extend this to the `QErr` record and the various `throwError` functions, but this is a much larger task and should probably be done in stages.
For now, `toErrorMessage` and `fromErrorMessage` are provided for conversion to and from `Text`, but the intent is to stop exporting these once all error messages are converted to the new type.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/5018
GitOrigin-RevId: 84b37e238992e4312255a87ca44f41af65e2d89a
### Description
The GraphQL spec has to conflicting requirements:
1. an object must contain at least one field: the schema may not contain empty objects
2. the _query_root_ must always be present
Given _1_, the schema generation code removes from the schema all fields that would result in empty objects, such as a table for which a user does not have select permissions. But, as a result, our code also potentially removes _query_root_ if it is empty, breaking _2_.
This PR introduces a dummy "placeholder" field in the query root if it's empty, to ensure we never remove it from the schema.
### Remaining work
- [x] changelog entry
- [x] tests
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/148
GitOrigin-RevId: bfd6bfcc2f3de92900b6ba566012f093399ca037
