Replace ExecuteSelectionSet with ExecuteGroupedFieldSet

spec/Section 5 -- Validation.md

@@ -463,7 +463,7 @@ unambiguous. Therefore any two field selections which might both be encountered
 for the same object are only valid if they are equivalent.
 
 During execution, the simultaneous execution of fields with the same response
-name is accomplished by {MergeSelectionSets()} and {CollectFields()}.
+name is accomplished by {CollectSubfields()}.
 
 For simple hand-written GraphQL, this rule is obviously a clear developer error,
 however nested fragments can make this difficult to detect manually.

spec/Section 6 -- Execution.md

@@ -131,12 +131,8 @@ ExecuteQuery(query, schema, variableValues, initialValue):
 - Let {queryType} be the root Query type in {schema}.
 - Assert: {queryType} is an Object type.
 - Let {selectionSet} be the top level Selection Set in {query}.
-- Let {data} be the result of running {ExecuteSelectionSet(selectionSet,
-  queryType, initialValue, variableValues)} _normally_ (allowing
-  parallelization).
-- Let {errors} be the list of all _field error_ raised while executing the
-  selection set.
-- Return an unordered map containing {data} and {errors}.
+- Return {ExecuteRootSelectionSet(variableValues, initialValue, queryType,
+  selectionSet)}.
 
 ### Mutation
 
@@ -153,11 +149,8 @@ ExecuteMutation(mutation, schema, variableValues, initialValue):
 - Let {mutationType} be the root Mutation type in {schema}.
 - Assert: {mutationType} is an Object type.
 - Let {selectionSet} be the top level Selection Set in {mutation}.
-- Let {data} be the result of running {ExecuteSelectionSet(selectionSet,
-  mutationType, initialValue, variableValues)} _serially_.
-- Let {errors} be the list of all _field error_ raised while executing the
-  selection set.
-- Return an unordered map containing {data} and {errors}.
+- Return {ExecuteRootSelectionSet(variableValues, initialValue, mutationType,
+  selectionSet, true)}.
 
 ### Subscription
 
@@ -300,12 +293,8 @@ ExecuteSubscriptionEvent(subscription, schema, variableValues, initialValue):
 - Let {subscriptionType} be the root Subscription type in {schema}.
 - Assert: {subscriptionType} is an Object type.
 - Let {selectionSet} be the top level Selection Set in {subscription}.
-- Let {data} be the result of running {ExecuteSelectionSet(selectionSet,
-  subscriptionType, initialValue, variableValues)} _normally_ (allowing
-  parallelization).
-- Let {errors} be the list of all _field error_ raised while executing the
-  selection set.
-- Return an unordered map containing {data} and {errors}.
+- Return {ExecuteRootSelectionSet(variableValues, initialValue,
+  subscriptionType, selectionSet)}.
 
 Note: The {ExecuteSubscriptionEvent()} algorithm is intentionally similar to
 {ExecuteQuery()} since this is how each event result is produced.
@@ -321,20 +310,44 @@ Unsubscribe(responseStream):
 
 - Cancel {responseStream}
 
-## Executing Selection Sets
+## Executing the Root Selection Set
+
+To execute the root selection set, the object value being evaluated and the
+object type need to be known, as well as whether it must be executed serially,
+or may be executed in parallel.
 
-To execute a selection set, the object value being evaluated and the object type
-need to be known, as well as whether it must be executed serially, or may be
-executed in parallel.
+Executing the root selection set works similarly for queries (parallel),
+mutations (serial), and subscriptions (where it is executed for each event in
+the underlying Source Stream).
 
-First, the selection set is turned into a grouped field set; then, each
-represented field in the grouped field set produces an entry into a response
-map.
+First, the selection set is turned into a grouped field set; then, we execute
+this grouped field set and return the resulting {data} and {errors}.
 
-ExecuteSelectionSet(selectionSet, objectType, objectValue, variableValues):
+ExecuteRootSelectionSet(variableValues, initialValue, objectType, selectionSet,
+serial):
 
+- If {serial} is not provided, initialize it to {false}.
 - Let {groupedFieldSet} be the result of {CollectFields(objectType,
   selectionSet, variableValues)}.
+- Let {data} be the result of running {ExecuteGroupedFieldSet(groupedFieldSet,
+  objectType, initialValue, variableValues)} _serially_ if {serial} is {true},
+  _normally_ (allowing parallelization) otherwise.
+- Let {errors} be the list of all _field error_ raised while executing the
+  selection set.
+- Return an unordered map containing {data} and {errors}.
+
+## Executing a Grouped Field Set
+
+To execute a grouped field set, the object value being evaluated and the object
+type need to be known, as well as whether it must be executed serially, or may
+be executed in parallel.
+
+Each represented field in the grouped field set produces an entry into a
+response map.
+
+ExecuteGroupedFieldSet(groupedFieldSet, objectType, objectValue,
+variableValues):
+
 - Initialize {resultMap} to an empty ordered map.
 - For each {groupedFieldSet} as {responseKey} and {fields}:
   - Let {fieldName} be the name of the first entry in {fields}. Note: This value
@@ -352,8 +365,8 @@ is explained in greater detail in the Field Collection section below.
 
 **Errors and Non-Null Fields**
 
-If during {ExecuteSelectionSet()} a field with a non-null {fieldType} raises a
-_field error_ then that error must propagate to this entire selection set,
+If during {ExecuteGroupedFieldSet()} a field with a non-null {fieldType} raises
+a _field error_ then that error must propagate to this entire selection set,
 either resolving to {null} if allowed or further propagated to a parent field.
 
 If this occurs, any sibling fields which have not yet executed or have not yet
@@ -691,8 +704,9 @@ CompleteValue(fieldType, fields, result, variableValues):
     - Let {objectType} be {fieldType}.
   - Otherwise if {fieldType} is an Interface or Union type.
     - Let {objectType} be {ResolveAbstractType(fieldType, result)}.
-  - Let {subSelectionSet} be the result of calling {MergeSelectionSets(fields)}.
-  - Return the result of evaluating {ExecuteSelectionSet(subSelectionSet,
+  - Let {groupedFieldSet} be the result of calling {CollectSubfields(objectType,
+    fields, variableValues)}.
+  - Return the result of evaluating {ExecuteGroupedFieldSet(groupedFieldSet,
     objectType, result, variableValues)} _normally_ (allowing for
     parallelization).
 
@@ -739,9 +753,9 @@ ResolveAbstractType(abstractType, objectValue):
 
 **Merging Selection Sets**
 
-When more than one field of the same name is executed in parallel, their
-selection sets are merged together when completing the value in order to
-continue execution of the sub-selection sets.
+When more than one field of the same name is executed in parallel, during value
+completion their selection sets are collected together to produce a single
+grouped field set in order to continue execution of the sub-selection sets.
 
 An example operation illustrating parallel fields with the same name with
 sub-selections.
@@ -760,14 +774,19 @@ sub-selections.
 After resolving the value for `me`, the selection sets are merged together so
 `firstName` and `lastName` can be resolved for one value.
 
-MergeSelectionSets(fields):
+CollectSubfields(objectType, fields, variableValues):
 
-- Let {selectionSet} be an empty list.
+- Let {groupedFieldSet} be an empty map.
 - For each {field} in {fields}:
   - Let {fieldSelectionSet} be the selection set of {field}.
   - If {fieldSelectionSet} is null or empty, continue to the next field.
-  - Append all selections in {fieldSelectionSet} to {selectionSet}.
-- Return {selectionSet}.
+  - Let {subGroupedFieldSet} be the result of {CollectFields(objectType,
+    fieldSelectionSet, variableValues)}.
+  - For each {subGroupedFieldSet} as {responseKey} and {subfields}:
+    - Let {groupForResponseKey} be the list in {groupedFieldSet} for
+      {responseKey}; if no such list exists, create it as an empty list.
+    - Append all fields in {subfields} to {groupForResponseKey}.
+- Return {groupedFieldSet}.
 
 ### Handling Field Errors