The simplification will allow us to avoid a few `MonadError QErr m` constsraints in the future - this effect can be created locally instead of reusing a global one.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/8729
GitOrigin-RevId: 851e28b1f5bfe4c47da43fa324714a941ef25c57
## Description
This change adds support for nested object fields in HGE IR and Schema Cache, the Data Connectors backend and API, and the MongoDB agent.
### Data Connector API changes
- The `/schema` endpoint response now includes an optional set of GraphQL type definitions. Table column types can refer to these definitions by name.
- Queries can now include a new field type `object` which contains a column name and a nested query. This allows querying into a nested object within a field.
### MongoDB agent changes
- Add support for querying into nested documents using the new `object` field type.
### HGE changes
- The `Backend` type class has a new type family `XNestedObjects b` which controls whether or not a backend supports querying into nested objects. This is currently enabled only for the `DataConnector` backend.
- For backends that support nested objects, the `FieldInfo` type gets a new constructor `FINestedObject`, and the `AnnFieldG` type gets a new constructor `AFNestedObject`.
- If the DC `/schema` endpoint returns any custom GraphQL type definitions they are stored in the `TableInfo` for each table in the source.
- During schema cache building, the function `addNonColumnFields` will check whether any column types match custom GraphQL object types stored in the `TableInfo`. If so, they are converted into `FINestedObject` instead of `FIColumn` in the `FieldInfoMap`.
- When building the `FieldParser`s from `FieldInfo` (function `fieldSelection`) any `FINestedObject` fields are converted into nested object parsers returning `AFNestedObject`.
- The `DataConnector` query planner converts `AFNestedObject` fields into `object` field types in the query sent to the agent.
## Limitations
### HGE not yet implemented:
- Support for nested arrays
- Support for nested objects/arrays in mutations
- Support for nested objects/arrays in order-by
- Support for filters (`where`) in nested objects/arrays
- Support for adding custom GraphQL types via track table metadata API
- Support for interface and union types
- Tests for nested objects
### Mongo agent not yet implemented:
- Generate nested object types from validation schema
- Support for aggregates
- Support for order-by
- Configure agent port
- Build agent in CI
- Agent tests for nested objects and MongoDB agent
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7844
GitOrigin-RevId: aec9ec1e4216293286a68f9b1af6f3f5317db423
### Description
(This PR is better reviewed commit by commit.)
This PR is an aggregation of small incremental changes to Pro's init:
- it deletes some dead code,
- it starts reorganizing the code of that file by sections, similar to OSS' init,
- it extracts and cleans up license key cache init (groups several blocks of code in one separate function)
- makes some changes to a service class to reduce the dependency on `_acAppStateRef`
This PR is a first step: our goal is to move the schema cache build _in_ the app monad, in order to achieve #8344. To do so, we will need to remove `_acAppStateRef` from Pro's `AppContext`. There are two different paths we can take from here, which is why i cut this PR here:
- the first would be to change the different instances we implement on `AppM` to take as an argument the parts of the schema cache they depend on, rather than reading them from `_acAppStateRef`; as of this PR, `MetricsConfig` is the only such field;
- the second would be to apply the same strategy we already used for the TLSAllowList, and use a `IORef` that can be updated after the schema cache is built; this change would have a smaller footprint, but introduces one new `IORef` per such field, which feels something we don't want to generalize
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/8655
GitOrigin-RevId: 809697d460bdb5c83ef7d30a2e835f589bcd80a6
### Description
If i understand correctly, the _value_ of a feature flag **can** change at runtime. Since this has an impact on how the schema cache is built, this PR makes the value of the flag a part of the cache's "dynamic" config, therefore making it an arrow-ish argument for the incremental framework. It also removes `CheckFeatureFlag` from the static config, now obsolete.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/8631
GitOrigin-RevId: 2ca898e4193e8552c40d2b21a819d3dd414601fe
### Description
This PR removes `ServerConfigCtx` and `HasServerConfigCtx`. Instead, it favours different approaches:
- when the code was only using one field, it passes that field explicitly (usually `SQLGenCtx` or `CheckFeatureFlag`)
- when the code was using several fields, but in only one function, it inlines
- for the cache build, it introduces `CacheStaticConfig` and `CacheDynamicConfig`, which are subsets of `AppEnv` and `AppContext` respectively
The main goal of this is to help with the modularization of the engine: as `ServerConfigCtx` had fields whose types were imported from several unrelated parts of the engine, using it tied together parts of the engine that should not be aware of one another (such as tying together `Hasura.LogicalModel` and `Hasura.GraphQL.Schema`).
The bulk of this PR is a change to the cache build, as a follow up to #8509: instead of giving the entire `ServerConfigCtx` as a incremental rule argument, we only give the new `CacheDynamicConfig` struct, which has fewer fields. The other required fields, that were coming from the `AppEnv`, are now given via the `HasCacheStaticConfig` constraint, which is a "subset" of `HasAppEnv`.
(Some further work could include moving `StringifyNumbers` out of `GraphQL.Schema.Options`, given how it is used all across the codebase, including in `RQL.DML`.)
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/8513
GitOrigin-RevId: 818cbcd71494e3cd946b06adbb02ca328a8a298e
- Remove `MonadMetadataStorageQueryAPI` which was only implemented by a default implementation
- Introduce `TransT` which can be used to easily derive `lift`ing implementations for `MonadBlaBlaBla` classes
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/8579
GitOrigin-RevId: 4f804fda7e2de5c9d75ee4df269f500ebd46b8c9
Also add a `default` implementation for `MonadQueryTags`.
This avoids a bunch of imports on `Hasura.GraphQL.Execute.Backend` which is a big module with lots of (transitive) dependencies.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/8571
GitOrigin-RevId: 8ecca452721b77953e6d088c79d8d6f003f2996f
## Description
This PR is a incremental step towards achieving the goal of #8344. It is a less ambitious version of #8484.
This PR removes all references to `HasServerConfigCtx` from the cache build and removes `ServerConfigCtx` from `CacheBuildParams`, making `ServerConfigCtx` an argument being passed around manually instead. This has several benefits: by making it an arrow argument, we now properly integrate the fields that change over time in the dependency framework, as they should be, and we can clean up some of the top-level app code.
## Implementation
In practice, this PR introduces a `HasServerConfigCtx` instance for `CacheRWT`, the monad we use to build the cache, so we can retrieve the `ServerConfigCtx` in the implementation of `CacheRWM`. This contributes to reducing the amount of `HasServerConfigCtx` in the code: we can remove `SchemaUpdateT` altogether, and we can remove the `HasServerConfigCtx` instance of `Handler`. This makes `HasServerConfigCtx` almost **an implementation detail of the Metadata API**.
This first step is enough to achieve the goal of #8344: we can now build the schema cache in the app monad, since we no longer rely on `HasServerConfigCtx` to build it.
## Drawbacks
This PR does not attempt to remove the use of `ServerConfigCtx` itself in the schema cache build: doing so would make this PR much much bigger. Ideally, to avoid having all the static fields given as arrow-ish arguments to the cache, we could depend on `HasAppEnv` in the cache build, and use `AppContext` as an arrow argument. But making the cache build depend on the full `AppEnv` and `AppContext` creates a lot of circular imports; and since removing `ServerConfigCtx` itself isn't required to achieve #8344, this PR keeps it wholesale and defers cleaning it to a future PR.
A negative consequence of this is that we need an `Eq` instance on `ServerConfigCtx`, and that instance is inelegant.
## Future work
There are several further steps we can take in parallel after this is merged. First, again, we can make a new version of #8344, removing `CacheBuild`, FINALLY. As for `ServerConfigCtx`, we can split it / rename it to make ad-hoc structures. If it turns out that `ServerConfigCtx` is only ever used for the schema cache build, we could split it between `CacheBuildEnv` and `CacheBuildContext`, which will be subsets of `AppEnv` and `AppContext`, avoiding import loops.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/8509
GitOrigin-RevId: 01b37cc3fd3490d6b117701e22fc4ac88b62b6b5
- Derive a few `instance`s
- Delete some dead code (methods and types)
- Delete some `INLINE` pragmas that are unlikely to have a big effect
- Monomorphize Postgres `LISTEN` code to avoid effect juggling
- Generalize some methods in `pg-client` so that others can be simplified
- Handle errors differently for `TxET` to deduplicate code
- Use `hoist` instead of specialized combinators such as `mapActionT`
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/8130
GitOrigin-RevId: bc1e908b6c0869f440a214a76744e92d40fea1e6
This PR is on top of #7789.
### Description
This PR entirely rewrites the API of the Tracing library, to make `interpTraceT` a thing of the past. Before this change, we ran traces by sticking a `TraceT` on top of whatever we were doing. This had several major drawbacks:
- we were carrying a bunch of `TraceT` across the codebase, and the entire codebase had to know about it
- we needed to carry a second class constraint around (`HasReporterM`) to be able to run all of those traces
- we kept having to do stack rewriting with `interpTraceT`, which went from inconvenient to horrible
- we had to declare several behavioral instances on `TraceT m`
This PR rewrite all of `Tracing` using a more conventional model: there is ONE `TraceT` at the bottom of the stack, and there is an associated class constraint `MonadTrace`: any part of the code that happens to satisfy `MonadTrace` is able to create new traces. We NEVER have to do stack rewriting, `interpTraceT` is gone, and `TraceT` and `Reporter` become implementation details that 99% of the code is blissfully unaware of: code that needs to do tracing only needs to declare that the monad in which it operates implements `MonadTrace`.
In doing so, this PR revealed **several bugs in the codebase**: places where we were expecting to trace something, but due to the default instance of `HasReporterM IO` we would actually not do anything. This PR also splits the code of `Tracing` in more byte-sized modules, with the goal of potentially moving to `server/lib` down the line.
### Remaining work
This PR is a draft; what's left to do is:
- [x] make Pro compile; i haven't updated `HasuraPro/Main` yet
- [x] document Tracing by writing a note that explains how to use the library, and the meaning of "reporter", "trace" and "span", as well as the pitfalls
- [x] discuss some of the trade-offs in the implementation, which is why i'm opening this PR already despite it not fully building yet
- [x] it depends on #7789 being merged first
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7791
GitOrigin-RevId: cadd32d039134c93ddbf364599a2f4dd988adea8
## Description
### I want to speak to the `Manager`
Oh boy. This PR is both fairly straightforward and overreaching, so let's break it down.
For most network access, we need a [`HTTP.Manager`](https://hackage.haskell.org/package/http-client-0.1.0.0/docs/Network-HTTP-Client-Manager.html). It is created only once, at the top level, when starting the engine, and is then threaded through the application to wherever we need to make a network call. As of main, the way we do this is not standardized: most of the GraphQL execution code passes it "manually" as a function argument throughout the code. We also have a custom monad constraint, `HasHttpManagerM`, that describes a monad's ability to provide a manager. And, finally, several parts of the code store the manager in some kind of argument structure, such as `RunT`'s `RunCtx`.
This PR's first goal is to harmonize all of this: we always create the manager at the root, and we already have it when we do our very first `runReaderT`. Wouldn't it make sense for the rest of the code to not manually pass it anywhere, to not store it anywhere, but to always rely on the current monad providing it? This is, in short, what this PR does: it implements a constraint on the base monads, so that they provide the manager, and removes most explicit passing from the code.
### First come, first served
One way this PR goes a tiny bit further than "just" doing the aforementioned harmonization is that it starts the process of implementing the "Services oriented architecture" roughly outlined in this [draft document](https://docs.google.com/document/d/1FAigqrST0juU1WcT4HIxJxe1iEBwTuBZodTaeUvsKqQ/edit?usp=sharing). Instead of using the existing `HasHTTPManagerM`, this PR revamps it into the `ProvidesNetwork` service.
The idea is, again, that we should make all "external" dependencies of the engine, all things that the core of the engine doesn't care about, a "service". This allows us to define clear APIs for features, to choose different implementations based on which version of the engine we're running, harmonizes our many scattered monadic constraints... Which is why this service is called "Network": we can refine it, moving forward, to be the constraint that defines how all network communication is to operate, instead of relying on disparate classes constraint or hardcoded decisions. A comment in the code clarifies this intent.
### Side-effects? In my Haskell?
This PR also unavoidably touches some other aspects of the codebase. One such example: it introduces `Hasura.App.AppContext`, named after `HasuraPro.Context.AppContext`: a name for the reader structure at the base level. It also transforms `Handler` from a type alias to a newtype, as `Handler` is where we actually enforce HTTP limits; but without `Handler` being a distinct type, any code path could simply do a `runExceptT $ runReader` and forget to enforce them.
(As a rule of thumb, i am starting to consider any straggling `runReaderT` or `runExceptT` as a code smell: we should not stack / unstack monads haphazardly, and every layer should be an opaque `newtype` with a corresponding run function.)
## Further work
In several places, i have left TODOs when i have encountered things that suggest that we should do further unrelated cleanups. I'll write down the follow-up steps, either in the aforementioned document or on slack. But, in short, at a glance, in approximate order, we could:
- delete `ExecutionCtx` as it is only a subset of `ServerCtx`, and remove one more `runReaderT` call
- delete `ServerConfigCtx` as it is only a subset of `ServerCtx`, and remove it from `RunCtx`
- remove `ServerCtx` from `HandlerCtx`, and make it part of `AppContext`, or even make it the `AppContext` altogether (since, at least for the OSS version, `AppContext` is there again only a subset)
- remove `CacheBuildParams` and `CacheBuild` altogether, as they're just a distinct stack that is a `ReaderT` on top of `IO` that contains, you guessed it, the same thing as `ServerCtx`
- move `RunT` out of `RQL.Types` and rename it, since after the previous cleanups **it only contains `UserInfo`**; it could be bundled with the authentication service, made a small implementation detail in `Hasura.Server.Auth`
- rename `PGMetadaStorageT` to something a bit more accurate, such as `App`, and enforce its IO base
This would significantly simply our complex stack. From there, or in parallel, we can start moving existing dependencies as Services. For the purpose of supporting read replicas entitlement, we could move `MonadResolveSource` to a `SourceResolver` service, as attempted in #7653, and transform `UserAuthenticationM` into a `Authentication` service.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7736
GitOrigin-RevId: 68cce710eb9e7d752bda1ba0c49541d24df8209f
## Description
This PR removes `MetadataStorageT`, and cleans up all top-level error handling. In short: this PR changes `MonadMetadataStorage` to explicitly return a bunch of `Either QErr a`, instead of relying on the stack providing a `MonadError QErr`. Since we implement that class on the base monad *below any ExceptT*, this removes a lot of very complicated instances that make assumptions about the shape of the stack.
On the back of this, we can remove several layers of ExceptT from the core of the code, including the one in `RunT`, which allows us to remove several instances of `liftEitherM . runExceptT`.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7689
GitOrigin-RevId: 97d600154d690f58c0b93fb4cc2d30fd383fd8b8
Hooks up event trigger codecs from #7237. This required fixing a problem where some backend types implemented `defaultTriggerOnReplication` with `error` which caused the server to crash when evaluating those for default values in codecs. The changes here add a type family to `Backend` called `XEventTriggers` that signals backend support for event triggers, and changes the type of `defaultTriggerOnReplication` to from `TriggerOnReplication` to `Maybe (XEventTriggers b, TriggerOnReplication)` so that it can only be implemented with a `Just` value if `XEventTriggers b` is inhabited. This emulates some existing type families in `Backend`. (Thanks to @daniel-chambers for this suggestion!)
I used the implementation of `defaultTriggerOnReplication` as a signal for event triggers support to prune the Metadata API so that event trigger fields will not appear in the OpenAPI spec for backend types that do not support event triggers. The codec version of the API will also not emit or accept those fields for those backend types. I think I could use `Typeable` to test whether `XEventTriggers` is `Void` instead of testing whether `defaultTriggerOnReplication` is `Nothing`. But the codec implementation will crash anyway if `defaultTriggerOnReplication` is `Nothing`.
I checked to make sure that graphql-engine-pro still compiles.
Ticket: https://hasurahq.atlassian.net/browse/GDC-521
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7295
GitOrigin-RevId: 2b2dd44291513266107ca25cf330319bf53a8b66
Codecs for event triggers, including webhook transforms. These are not hooked into the higher-up table metadata codec yet because some backend implementations implement event triggers with `error` which causes an error when codecs are evaluated. I plan to follow up with another PR to resolve that.
Ticket: https://hasurahq.atlassian.net/browse/GDC-585
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7237
GitOrigin-RevId: 8ce40fe6fedcf8b109d6ca50a505333df855a8ce
Generate more Metadata Inconsistencies instead of startup failures. Specifically this means that
- errors retrieving the main query of an executable GraphQL document, and
- errors during fragment inlining
no longer fail irrecoverably.
This also makes more parts of `buildSchemaCacheRule` into pure code, which is always nice.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7234
GitOrigin-RevId: aebf636c2fb1aad1c2df9a37f7d0b67c1ee40c42
`toLazyByteString` is a little deficient in two ways:
- It allocates relatively large chunks (4KB + 32KB +32KB, etc…) which is wasteful for small ByteStrings
- It shrinks each chunk (Copying the data to a new chunk of exactly the right size) if it's not more than half filled. If we're running the builder right before we send it over the wire, this copy is totally extraneous (we simply end up with more work for the next GC)
part of the effort: https://github.com/hasura/graphql-engine-mono/issues/5518
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7187
GitOrigin-RevId: b499cd49c33da6cfee96be629a36b5c812486e39
Dependencies seem to get concatenated very often, so let's use a data structure that supports efficient concatenation.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7050
GitOrigin-RevId: 6331963f99f17d1b908a6038318d8c4834cf4dd7
## Description ✍️
This PR adds support to generate query params directly using a kriti template which can be used to flatten a list of parameter arguments as well.
### Changes in the Metadata API
Earlier the `query_params` key inside `request_transform` used to take in an object of key/value pairs where the `key` represents the query parameter name and `value` points to the value of the parameter or a kriti template which could be resolved to the value.
With this PR, we provide the user with more freedom to generate the complete query string using kriti template. The `query_params` can now take in a string as well which will be a kriti template. This new change needs to be incorporated on the console and CLI metadata import/export as well.
- [x] CLI: Compatible, no changes required
- [ ] Console
## Changelog ✍️
__Component__ : server
__Type__: feature
__Product__: community-edition
### Short Changelog
use kriti template to generate query param from list of arguments
### Related Issues ✍
https://hasurahq.atlassian.net/browse/GS-243
### Solution and Design ✍
We use a kriti template to generate the complete query parameter string.
| Query Template | Output |
|---|---|
| `{{ concat ([concat({{ range _, x := [\"apple\", \"banana\"] }} \"tags={{x}}&\" {{ end }}), \"flag=smthng\"]) }}`| `tags=apple&tags=banana&flag=smthng` |
| `{{ concat ([\"tags=\", concat({{ range _, x := $body.input }} \"{{x}},\" {{ end }})]) }}` | `tags=apple%2Cbanana%2C` |
### Steps to test and verify ✍
- start HGE and make the following request to `http://localhost:8080/v1/metadata`:
```json
{
"type": "test_webhook_transform",
"args": {
"webhook_url": "http://localhost:3000",
"body": {
"action": {
"name": "actionName"
},
"input": ["apple", "banana"]
},
"request_transform": {
"version": 2,
"url": "{{$base_url}}",
"query_params": "{{ concat ([concat({{ range _, x := $body.input }} \"tags={{x}}&\" {{ end }}), \"flag=smthng\"]) }}",
"template_engine": "Kriti"
}
}
}
```
- you should receive the following as output:
```json
{
"body": {
"action": {
"name": "actionName"
},
"input": [
"apple",
"banana"
]
},
"headers": [],
"method": "GET",
"webhook_url": "http://localhost:3000?tags=apple&tags=banana&flag=smthng"
}
```
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/6961
Co-authored-by: Tirumarai Selvan <8663570+tirumaraiselvan@users.noreply.github.com>
GitOrigin-RevId: 712ba038f03009edc3e8eb0435e723304943399a
## Description ✍️
This PR introduces a new feature to enable/disable event triggers during logical replication of table data for PostgreSQL and MS-SQL data sources. We introduce a new field `trigger_on_replication` in the `*_create_event_trigger` metadata API. By default the event triggers will not fire for logical data replication.
## Changelog ✍️
__Component__ : server
__Type__: feature
__Product__: community-edition
### Short Changelog
Add option to enable/disable event triggers on logically replicated tables
### Related Issues ✍
https://github.com/hasura/graphql-engine/issues/8814https://hasurahq.atlassian.net/browse/GS-252
### Solution and Design
- By default, triggers do **not** fire when the session mode is `replica` in Postgres, so if the `triggerOnReplication` is set to `true` for an event trigger we run the query `ALTER TABLE #{tableTxt} ENABLE ALWAYS TRIGGER #{triggerNameTxt};` so that the trigger fires always irrespective of the `session_replication_role`
- By default, triggers do fire in case of replication in MS-SQL, so if the `triggerOnReplication` is set to `false` for an event trigger we add a clause `NOT FOR REPLICATION` to the the SQL when the trigger is created/altered, which sets the `is_not_for_replication` for the trigger as `true` and it does not fire during logical replication.
### Steps to test and verify ✍
- Run hspec integration tests for HGE
## Server checklist ✍
### Metadata ✍
Does this PR add a new Metadata feature?
- ✅ Yes
- Does `export_metadata`/`replace_metadata` supports the new metadata added?
- ✅
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/6953
Co-authored-by: Puru Gupta <32328846+purugupta99@users.noreply.github.com>
Co-authored-by: Sean Park-Ross <94021366+seanparkross@users.noreply.github.com>
GitOrigin-RevId: 92731328a2bbdcad2302c829f26f9acb33c36135
Mostly trying to avoid tricky `Arrows` syntax, and unnecessary use of the `Hasura.Incremental` framework.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/6997
GitOrigin-RevId: 9a2f5883e7e29af164e1581049ae003afec2cbe4
I encountered this dead code while doing other things: it's a type class with a single method which is never called. Deleting the type class allows us to simplify `TableCoreCacheRT` and `TableCacheRT`
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7075
GitOrigin-RevId: 121320349c478a93717b0706037553d8406cbfa9
This increases the speed of `create_query_collection` and `add_collection_to_allowlist` by a factor ~~10~~ 65, by caching the in-memory GraphQL schema. This speedup also applies more broadly to Metadata changes relating to:
- allowlists
- query collections
- cron triggers
- REST endpoints
- API limits
- metrics config
- GraphQL introspection options
- TLS allow lists
- OpenTelemetry
When is construction of the in-memory GraphQL schema cached between Metadata operations?
Before this PR, **never**! It's rebuilt fully, for every role, on every Metadata operation.
However, there are many Metadata operations that don't influence the GraphQL schema. So we should be caching its construction.
The `Hasura.Incremental` framework allows us to cache such constructions: whenever we have an arrow `Rule m a b`, where `a` is the input to the arrow and `b` the output, we can use the `Inc.cache` combinator to obtain a new arrow which is only re-executed when the input `a` changes in a material way. To test this, `a` needs an `Eq` instance. (Before hasura/graphql-engine-mono#6877, this was a `Cacheable` type class which has now been removed.)
We can't simply apply `Inc.cache` to the "Steps 3 and 4" in `buildSchemaCacheRule`, because the inputs (components of `BuildOutputs` such as `SourceCache`) don't have an `Eq` instance.
So the changes to `buildSchemaCacheRule` restructure the code so that the input to "Step 1", namely the Metadata, can be used as a caching key instead, so that `Inc.cache` can be applied to the whole sequence of steps.
That works to cache construction of the GraphQL schema, but it means that now only those Metadata operations that _don't_ influence any of the products of steps 1-4 can use a cached build of the GraphQL schema. The most important intermediate product is `BuildOutputs`. So now the exercise becomes to minimize the amount of stuff stored in `BuildOutputs`, so that as many Metadata operations as possible can be handled outside of the codepath that produces a GraphQL schema.
Per hasura/graphql-engine-mono#6609, the `BuildOutputs` structure is too big, and stores things unnecessarily. Refer to the PR description there for reasoning - the same logic applies to this PR, and simply goes a few steps further. In doing so, it can benefit from hasura/graphql-engine-mono#6765, which allows us to verify at compile time that certain Schema Cache building steps _don't_ generate "Metadata dependencies". If a certain Metadata dependency is never generated, we don't need to handle that case in `deleteMetadataObject`. Thus such intermediate products don't need to be passed through `resolveDependencies`, and thus they don't need to be stored in `BuildOutputs`, and thus their rebuild won't trigger a GraphQL schema rebuild.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/6613
GitOrigin-RevId: 27d2e69d3461bd4c32f08febef9995c0369fab3a
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
