Change ExecuteSelectionSet to ExecuteGroupedFieldSet

Author: benjie

spec/Section 6 -- Execution.md

@@ -321,31 +321,34 @@ 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, we execute
+this grouped field set and return the resulting {data} and {errors}.
+
 ExecuteRootSelectionSet(variableValues, initialValue, objectType, selectionSet,
 serial):
 
 - If {serial} is not provided, initialize it to {false}.
-- Let {data} be the result of running {ExecuteSelectionSet(selectionSet,
+- 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 Selection Sets
+## Executing a Grouped Field Set
 
-To execute a _selection set_, the object value being evaluated and the object
+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.
 
-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.
+Each represented field in the grouped field set produces an entry into a
+response map.
 
-ExecuteSelectionSet(selectionSet, objectType, objectValue, variableValues):
+ExecuteGroupedFieldSet(groupedFieldSet, objectType, objectValue,
+variableValues):
 
-- Let {groupedFieldSet} be the result of {CollectFields(objectType,
-  selectionSet, 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
@@ -363,8 +366,8 @@ 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
@@ -704,8 +707,9 @@ 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).
 
@@ -752,9 +756,9 @@ ResolveAbstractType(abstractType, objectValue):
 
 **Merging Selection Sets**
 
-When more than one field of the same name is executed in parallel, the
-_selection set_ for each of the fields 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.
@@ -773,14 +777,19 @@ 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