### Description
Each Backend executes queries against the database in a slightly different stack: Postgres uses its own `TXeT`, MSSQL uses a variant of it, BigQuery is simply in `ExceptT QErr IO`... To accommodate those variations, we had originally introduced an `ExecutionMonad b` type family in `BackendExecute`, allowing each backend to describe its own stack. It was then up to that backend's `BackendTransport` instance to implement running said stack, and converting the result back into our main app monad.
However, this was not without complications: `TraceT` is one of them: as it usually needs to be on the top of the stack, converting from one stack to the other implies the use `interpTraceT`, which is quite monstrous. Furthermore, as part of the Entitlement Services work, we're trying to move to a "Services" architecture in which the entire engine runs in one base monad, that delegates features and dependencies to monad constraints; and as a result we'd like to minimize the number of different monad stacks we have to maintain and translate from and to in the codebase.
To improve things, this PR changes `ExecutionMonad b` from an _absolute_ stack to a _relative_ one: i.e.: what needs to be stacked on top of our base monad for the execution. In `Transport`, we then only need to pop the top of the stack, and voila. This greatly simplifies the implementation of the backends, as there's no longer any need to do any stack transformation: MySQL's implementation becomes a `runIdentityT`! This also removes most mentions of `TraceT` from the execution code since it's no longer required: we can rely on the base monad's existing `MonadTrace` constraint.
To continue encapsulating monadic actions in `DBStepInfo` and avoid threading a bunch of `forall` all over the place, this PR introduces a small local helper: `OnBaseMonad`. One only downside of all this is that this requires adding `MonadBaseControl IO m` constraint all over the place: previously, we would run directly on `IO` and lift, and would therefore not need to bring that constraint all the way.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7789
GitOrigin-RevId: e9b2e431c5c47fa9851abf87545c0415ff6d1a12
>
## Description ✍️
->
Fleshes out the Capabilities types used by Data Connector agents.
### Related Issues ✍
->
https://hasurahq.atlassian.net/browse/GDW-85
### Solution and Design ✍
>
Capabilities are divided into sections for queries, mutation, subscriptions, filtering and relationships:
```haskell
data Capabilities = Capabilities
{ cQueries :: Maybe QueryCapabilities,
cMutations :: Maybe MutationCapabilities,
cSubscriptions :: Maybe SubscriptionCapabilities,
cFiltering :: Maybe FilteringCapabilities,
cRelationships :: Maybe RelationshipCapabilities
}
```
Each section is optional. If the section is absent it means the the related capabilities are not supported by the agent.
The types for each section can contain additional details about exactly what is supported. E.g.
```haskell
data QueryCapabilities = QueryCapabilities
{ qcSupportsPrimaryKeys :: Bool
}
```
These are currently mostly empty, but will be filled in later.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/4671
GitOrigin-RevId: 3d48570266bfce5e177a543a0ed6f63a7b450f0b
>
## Description ✍️
- Creates a new `/capabilities` endpoint for the GDC agent API
- Removes capabilities from the `/schema` endpoint
- Removes the `/config-schema` endpoint and includes the `ConfigSchemaResponse` within the `CapabilitiesResponse`
### Related Issues ✍
->
https://hasurahq.atlassian.net/browse/GDW-85
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/4478
GitOrigin-RevId: 426662ee9e751343d94207d439a5025df65d2de7
