The issue is similar to the one in #1513:
```
src/Servant/Server/Internal.hs:824:10: error:
• Uninferrable type variable k0 in
type family equation right-hand side: (TypeError ...)
• In the type instance declaration for ‘ServerT’
In the instance declaration for
‘HasServer ((arr :: a -> b) :> sub) context’
|
824 | type ServerT (arr :> sub) _ = TypeError (PartialApplication HasServer arr)
|
```
This fix is similar to the one in #1514.
Move `HasServer (NamedRoutes routes)` instance
The instance has been moved to `Servant.Server.Internal`, as the
instances for other combinators. It is necessary so that the instance
can be re-exported from `Servant.Server` without circular imports.
Otherwise, users have to import `Servant.Server.Generic` manually ;
forgetting to do so will produce confusing error messages about the
missing instance.
Move `HasClient (NamedRoutes routes)` instance
Moved so that the instance is made available when importing
`Servant.Client`, avoiding possibly confusing errors when
`Servant.Client.Generic` isn't imported.
QuantifiedConstraints isn't available for GHC 8.4 (where our GHCJS
version is still stuck).
We may need to take a drastic decision for GHCJS at some point.
We define `ServerT (NamedRoutes api) m` as `api (AsServerT m)`, so that
the server of an record-defined API is a record of handlers.
The implementation piggy backs on the instance for “vanilla” servant
types with `(:<|>)`, using the `GServantProduct` for converting backd
and forth between the record / vanilla servers.
The main difficulty is that GHC needs to know that this operation is
legit, which can be expressed as the fact that:
```
GToServant (Rep (ServerT (NamedRoutes api))) m ~
ServerT (GToServant (Rep (api AsApi))) m
```
plus a few additional constraints.
This is easy enough for `route`, as we know that `m ~ Handler`. But in
the case of `hoistServerWithContext`, the two involved monads are
unknown ; in other words, this constraint needs to hold `forall m.`
Switching `-XQuantifiedConstraints` on is not sufficient, as our
constraints involve type families (`Rep` and `ServerT`). Our trick is to
use an intermediary typeclass, `GServer`, as a provider of evidence (in
the form of a `Dict`) that our constraints are indeed satisfied for a
particular monad.
The only instance of `GServer` is defined along with it, so it is
practically invisible to users.
ServerError field errBody uses ByteString, whose IsString instance kills
Unicode, thus turning example into garbage. Changed it to simple ASCII
string, since Unicode art did not exactly correspond to 404 error
anyway.
Fixes#1371
Currently there is no way for Servant users to customize formatting of
error messages that arise when combinators can't parse URL or request
body, apart from reimplementing those combinators for themselves or
using middlewares.
This commit adds a possibility to specify custom error formatters
through Context.
Fixes#685
This commit adds an explanation and a link to the Servant Cookbook
to `genericServerT`.
Moreover, the `genericServer` and `genericServe`'s haddocks are
slightly edited to add a missing 'a'.
- Almost everything 0.15; also servant-foreign jumped to 0.15, for
consistency
- Bump lower bounds of dependencies to most recent versions atm
- Use hspec-2.6.0
- Update `stack.yaml` accordingly
- Use base-compat a bit more
- Drop aeson-compat dependency (in tests and tutorial)
- Introduce SourceT, which is simple variant of "correct `ListT`".
There are another variants possible (like in `streaming`),
but I'm not sure there's much real difference.
- Introduce `Codensity`. There's a flag if people don't want to depend
on `kan-extensions`.
- `StreamGenerator` and `ResultStream` are both `SourceT`.
`Stream` combinator in `servant-client` uses `Codensity` for CPS.
- Add servant-machines, servant-conduit, servant-pipes
- Add streaming cookbook: just code, no explanations.
- Add a script to run streaming 'benchmarks'
In case that a sub-server doesn't support the content-type specified
in the request invoke `delayedFail` instead of `delayedFailFatal` in
order to give the chance to other sub-servers to handle the request.
