What is the `Cacheable` type class about?
```haskell
class Eq a => Cacheable a where
unchanged :: Accesses -> a -> a -> Bool
default unchanged :: (Generic a, GCacheable (Rep a)) => Accesses -> a -> a -> Bool
unchanged accesses a b = gunchanged (from a) (from b) accesses
```
Its only method is an alternative to `(==)`. The added value of `unchanged` (and the additional `Accesses` argument) arises _only_ for one type, namely `Dependency`. Indeed, the `Cacheable (Dependency a)` instance is non-trivial, whereas every other `Cacheable` instance is completely boilerplate (and indeed either generated from `Generic`, or simply `unchanged _ = (==)`). The `Cacheable (Dependency a)` instance is the only one where the `Accesses` argument is not just passed onwards.
The only callsite of the `unchanged` method is in the `ArrowCache (Rule m)` method. That is to say that the `Cacheable` type class is used to decide when we can re-use parts of the schema cache between Metadata operations.
So what is the `Cacheable (Dependency a)` instance about? Normally, the output of a `Rule m a b` is re-used when the new input (of type `a`) is equal to the old one. But sometimes, that's too coarse: it might be that a certain `Rule m a b` only depends on a small part of its input of type `a`. A `Dependency` allows us to spell out what parts of `a` are being depended on, and these parts are recorded as values of types `Access a` in the state `Accesses`.
If the input `a` changes, but not in a way that touches the recorded `Accesses`, then the output `b` of that rule can be re-used without recomputing.
So now you understand _why_ we're passing `Accesses` to the `unchanged` method: `unchanged` is an equality check in disguise that just needs some additional context.
But we don't need to pass `Accesses` as a function argument. We can use the `reflection` package to pass it as type-level context. So the core of this PR is that we change the instance declaration from
```haskell
instance (Cacheable a) => Cacheable (Dependency a) where
```
to
```haskell
instance (Given Accesses, Eq a) => Eq (Dependency a) where
```
and use `(==)` instead of `unchanged`.
If you haven't seen `reflection` before: it's like a `MonadReader`, but it doesn't require a `Monad`.
In order to pass the current `Accesses` value, instead of simply passing the `Accesses` as a function argument, we need to instantiate the `Given Accesses` context. We use the `give` method from the `reflection` package for that.
```haskell
give :: forall r. Accesses -> (Given Accesses => r) -> r
unchanged :: (Given Accesses => Eq a) => Accesses -> a -> a -> Bool
unchanged accesses a b = give accesses (a == b)
```
With these three components in place, we can delete the `Cacheable` type class entirely.
The remainder of this PR is just to remove the `Cacheable` type class and its instances.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/6877
GitOrigin-RevId: 7125f5e11d856e7672ab810a23d5bf5ad176e77f
This upgrades the version of Ormolu required by the HGE repository to v0.5.0.1, and reformats all code accordingly.
Ormolu v0.5 reformats code that uses infix operators. This is mostly useful, adding newlines and indentation to make it clear which operators are applied first, but in some cases, it's unpleasant. To make this easier on the eyes, I had to do the following:
* Add a few fixity declarations (search for `infix`)
* Add parentheses to make precedence clear, allowing Ormolu to keep everything on one line
* Rename `relevantEq` to `(==~)` in #6651 and set it to `infix 4`
* Add a few _.ormolu_ files (thanks to @hallettj for helping me get started), mostly for Autodocodec operators that don't have explicit fixity declarations
In general, I think these changes are quite reasonable. They mostly affect indentation.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/6675
GitOrigin-RevId: cd47d87f1d089fb0bc9dcbbe7798dbceedcd7d83
This moves `MkTypename` and `NamingCase` into their own modules, with the intent of reducing the scope of the schema parsers code, and trying to reduce imports of large modules when small ones will do.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/4978
GitOrigin-RevId: 19541257fe010035390f6183a4eaa37bae0d3ca1
## Description
This PR removes `RQL.Types`, which was now only re-exporting a bunch of unrelated modules.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/4363
GitOrigin-RevId: 894f29a19bff70b3dad8abc5d9858434d5065417
