Split up apollo and relay stages (#815)

<!-- The PR description should answer 2 (maybe 3) important questions:
-->

### What

In the haste of breaking things up, realised we put the `relay` checks
in with the `apollo` ones where they are two separate things.

<!-- What is this PR trying to accomplish (and why, if it's not
obvious)? -->

<!-- Consider: do we need to add a changelog entry? -->

### How

Split up `apollo` step into `relay` and `apollo` steps. Functional
no-op.

<!-- How is it trying to accomplish it (what are the implementation
steps)? -->

V3_GIT_ORIGIN_REV_ID: 8d02d3cb77b1248239be37ed61d0b87b9b734fdf

v3/crates/metadata-resolve/src/stages/apollo/mod.rs

@@ -1,6 +1,6 @@
 use std::collections::BTreeMap;
 
-use open_dds::{models::ModelName, types::CustomTypeName};
+use open_dds::types::CustomTypeName;
 
 use crate::types::error::Error;
 
@@ -11,22 +11,11 @@ use crate::types::subgraph::Qualified;
 /// Ideally, we could move more Apollo-based resolving into this discreet step, haven't
 /// investigated this too deeply yet.
 pub fn resolve(
-    global_id_enabled_types: &BTreeMap<Qualified<CustomTypeName>, Vec<Qualified<ModelName>>>,
     apollo_federation_entity_enabled_types: &BTreeMap<
         Qualified<CustomTypeName>,
         Option<Qualified<open_dds::models::ModelName>>,
     >,
 ) -> Result<(), Error> {
-    // To check if global_id_fields are defined in object type but no model has global_id_source set to true:
-    //   - Throw an error if no model with globalIdSource:true is found for the object type.
-    for (object_type, model_name_list) in global_id_enabled_types {
-        if model_name_list.is_empty() {
-            return Err(Error::GlobalIdSourceNotDefined {
-                object_type: object_type.clone(),
-            });
-        }
-    }
-
     // To check if apollo federation entity keys are defined in object type but no model has
     // apollo_federation_entity_source set to true:
     //   - Throw an error if no model with apolloFederation.entitySource:true is found for the object type.

v3/crates/metadata-resolve/src/stages/mod.rs

@@ -13,6 +13,7 @@ pub mod models_graphql;
 pub mod object_boolean_expressions;
 pub mod object_types;
 pub mod relationships;
+mod relay;
 pub mod roles;
 pub mod scalar_boolean_expressions;
 pub mod scalar_types;
@@ -146,10 +147,9 @@ pub fn resolve(
         &boolean_expression_types,
     )?;
 
-    apollo::resolve(
-        &global_id_enabled_types,
-        &apollo_federation_entity_enabled_types,
-    )?;
+    apollo::resolve(&apollo_federation_entity_enabled_types)?;
+
+    relay::resolve(&global_id_enabled_types)?;
 
     let object_types_with_relationships = relationships::resolve(
         &metadata_accessor,

v3/crates/metadata-resolve/src/stages/relay/mod.rs

@@ -0,0 +1,27 @@
+use std::collections::BTreeMap;
+
+use open_dds::{models::ModelName, types::CustomTypeName};
+
+use crate::types::error::Error;
+
+use crate::types::subgraph::Qualified;
+
+/// This isn't a particularly satisfying resolve step, as it only serves to validate
+/// the output of previous steps.
+/// Ideally, we could move more Relay-based resolving into this discreet step, haven't
+/// investigated this too deeply yet.
+pub fn resolve(
+    global_id_enabled_types: &BTreeMap<Qualified<CustomTypeName>, Vec<Qualified<ModelName>>>,
+) -> Result<(), Error> {
+    // To check if global_id_fields are defined in object type but no model has global_id_source set to true:
+    //   - Throw an error if no model with globalIdSource:true is found for the object type.
+    for (object_type, model_name_list) in global_id_enabled_types {
+        if model_name_list.is_empty() {
+            return Err(Error::GlobalIdSourceNotDefined {
+                object_type: object_type.clone(),
+            });
+        }
+    }
+
+    Ok(())
+}