Default value coercion rules

Author: benjie

spec/Section 6 -- Execution.md

@@ -89,8 +89,12 @@ CoerceVariableValues(schema, operation, variableValues):
     * Let {value} be the value provided in {variableValues} for the
       name {variableName}.
     * If {hasValue} is not {true} and {defaultValue} exists (including {null}):
+      * If {defaultValue} cannot be coerced according to the input coercion
+        rules of {variableType}, throw a query error.
+      * Let {coercedDefaultValue} be the result of coercing {defaultValue} according to the
+        input coercion rules of {variableType}.
       * Add an entry to {coercedValues} named {variableName} with the
-        value {defaultValue}.
+        value {coercedDefaultValue}.
     * Otherwise if {variableType} is a Non-Nullable type, and either {hasValue}
       is not {true} or {value} is {null}, throw a query error.
     * Otherwise if {hasValue} is true:
@@ -586,8 +590,12 @@ CoerceArgumentValues(objectType, field, variableValues):
         name {variableName}.
     * Otherwise, let {value} be {argumentValue}.
     * If {hasValue} is not {true} and {defaultValue} exists (including {null}):
+      * If {defaultValue} cannot be coerced according to the input coercion
+        rules of {variableType}, throw a query error.
+      * Let {coercedDefaultValue} be the result of coercing {defaultValue} according to the
+        input coercion rules of {variableType}.
       * Add an entry to {coercedValues} named {argumentName} with the
-        value {defaultValue}.
+        value {coercedDefaultValue}.
     * Otherwise if {argumentType} is a Non-Nullable type, and either {hasValue}
       is not {true} or {value} is {null}, throw a field error.
     * Otherwise if {hasValue} is true: