Change ExecuteSelectionSet to ExecuteGroupedFieldSet

Author: benjie

spec/Section 6 -- Execution.md

@@ -320,31 +320,34 @@ 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 type
-need to be known, as well as whether it must be executed serially, or may be
-executed in parallel.
+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
@@ -362,8 +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
@@ -701,8 +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).
 
@@ -749,9 +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.
@@ -770,14 +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