[RFC] Ordering of queried fields

This removes language referring to responses as unordered. In fact responses should always be ordered in the order in which they were queried.

This adds clarifying language around both object types and input objects about ordering and provides more examples.

I've also added a caveat that response formats which don't support ordering are not required to uphold it.

**Impact:**

Some servers may return responses in an unordered fashion due to the way their executor behaves, though most which are ported from or inspired by graphql-js, our reference implementation, already behave this way.

**Motivation:**

This enables custom parsers which expect JSON values to be a very specific shape for performance reasons, but it also ensures an easier level of understandability when a response's shape so tightly matches the query - both for new learners and for debugging.

spec/Section 2 -- Language.md

@@ -779,6 +779,25 @@ curly-braces `{ }`.  The values of an object literal may be any input value
 literal or variable (ex. `{ name: "Hello world", score: 1.0 }`). We refer to
 literal representation of input objects as "object literals."
 
+**Input object fields are unordered**
+
+Input object fields may be provided in any syntactic order and maintain
+identical semantic meaning.
+
+These two queries are semantically identical:
+
+```graphql
+{
+  nearestThing(location: { lon: 12.43, lat: -53.211 })
+}
+```
+
+```graphql
+{
+  nearestThing(location: { lat: -53.211, lon: 12.43 })
+}
+```
+
 **Semantics**
 
 ObjectValue : { }

spec/Section 3 -- Type System.md

@@ -234,9 +234,9 @@ While Scalar types describe the leaf values of these hierarchical queries, Objec
 describe the intermediate levels.
 
 GraphQL Objects represent a list of named fields, each of which yield a value of
-a specific type. Object values are serialized as unordered maps, where the
+a specific type. Object values are serialized as ordered maps, where the
 queried field names (or aliases) are the keys and the result of evaluating
-the field is the value.
+the field is the value, ordered by the order in which they appear in the query.
 
 For example, a type `Person` could be described as:
 
@@ -253,9 +253,9 @@ that will yield an `Int` value, and `picture` a field that will yield a
 `Url` value.
 
 A query of an object value must select at least one field. This selection of
-fields will yield an unordered map containing exactly the subset of the object
-queried. Only fields that are declared on the object type may validly be queried
-on that object.
+fields will yield an ordered map containing exactly the subset of the object
+queried, in the order in which they were queried. Only fields that are declared
+on the object type may validly be queried on that object.
 
 For example, selecting all the fields of `Person`:
 
@@ -281,17 +281,17 @@ While selecting a subset of fields:
 
 ```graphql
 {
-  name
   age
+  name
 }
 ```
 
 Must only yield exactly that subset:
 
 ```js
 {
-  "name": "Mark Zuckerberg",
-  "age": 30
+  "age": 30,
+  "name": "Mark Zuckerberg"
 }
 ```
 
@@ -342,6 +342,99 @@ And will yield the subset of each object type queried:
 }
 ```
 
+**Field Ordering**
+
+When querying an Object, the resulting mapping of fields are conceptually
+ordered in the same order in which they were encountered during query execution,
+excluding fragments for which the type does not apply and fields or
+fragments that are skipped via `@skip` or `@include` directives. This ordering
+is correctly produced when using the {CollectFields()} algorithm.
+
+Response formats which support ordered maps (such as JSON) must maintain this
+ordering. Response formats which do not support ordered maps may disregard
+this ordering.
+
+If a fragment is spread before other fields, the fields that fragment specifies
+occur in the response before the following fields.
+
+```graphql
+{
+  foo
+  ...Frag
+  qux
+}
+
+fragment Frag on Query {
+  bar
+  baz
+}
+```
+
+Produces the ordered result:
+
+```js
+{
+  "foo": 1,
+  "bar": 2,
+  "baz": 3,
+  "qux": 4
+}
+```
+
+If a field is queried multiple times in a selection, it is ordered by the first
+time it is encountered. However fragments for which the type does not apply does
+not affect ordering.
+
+```graphql
+{
+  foo
+  ...Ignored
+  ...Matching
+  bar
+}
+
+fragment Ignored on UnknownType {
+  qux
+  baz
+}
+
+fragment Matching on Query {
+  bar
+  qux
+  foo
+}
+```
+
+Produces the ordered result:
+
+```js
+{
+  "foo": 1,
+  "bar": 2,
+  "qux": 3
+}
+```
+
+Also, if directives result in fields being excluded, they are not considered in
+the ordering of fields.
+
+```graphql
+{
+  foo @skip(if: true)
+  bar
+  foo
+}
+```
+
+Produces the ordered result:
+
+```js
+{
+  "bar": 1,
+  "foo": 2
+}
+```
+
 **Result Coercion**
 
 Determining the result of coercing an object is the heart of the GraphQL

spec/Section 6 -- Execution.md

@@ -50,20 +50,20 @@ The selection set is converted to a grouped field set by calling
 
 CollectFields(objectType, selectionSet, visitedFragments):
 
-  * Initialize {groupedFields} to an empty list of lists.
+  * Initialize {groupedFields} to an empty ordered list of lists.
   * For each {selection} in {selectionSet};
     * If {selection} provides the directive `@skip`, let {skipDirective} be that directive.
       * If {skipDirective}'s {if} argument is {true}, continue with the
         next {selection} in {selectionSet}.
     * If {selection} provides the directive `@include`, let {includeDirective} be that directive.
       * If {includeDirective}'s {if} argument is {false}, continue with the
         next {selection} in {selectionSet}.
-    * If {selection} is a Field:
+    * If {selection} is a {Field}:
       * Let {responseKey} be the response key of {selection}.
       * Let {groupForResponseKey} be the list in {groupedFields} for
         {responseKey}; if no such list exists, create it as an empty list.
       * Append {selection} to the {groupForResponseKey}.
-    * If {selection} is a FragmentSpread:
+    * If {selection} is a {FragmentSpread}:
       * Let {fragmentSpreadName} be the name of {selection}.
       * If {fragmentSpreadName} is in {visitedFragments}, continue with the
         next {selection} in {selectionSet}.
@@ -76,20 +76,20 @@ CollectFields(objectType, selectionSet, visitedFragments):
       * If {doesFragmentTypeApply(objectType, fragmentType)} is false, continue
         with the next {selection} in {selectionSet}.
       * Let {fragmentSelectionSet} be the top-level selection set of {fragment}.
-      * Let {fragmentGroupedFields} be the result of calling
-        {CollectFields(objectType, fragmentSelectionSet)}.
-      * For each {fragmentGroup} in {fragmentGroupedFields}:
+      * Let {fragmentGroupedFieldSet} be the result of calling
+        {CollectFields(objectType, fragmentSelectionSet, visitedFragments)}.
+      * For each {fragmentGroup} in {fragmentGroupedFieldSet}:
         * Let {responseKey} be the response key shared by all fields in {fragmentGroup}
         * Let {groupForResponseKey} be the list in {groupedFields} for
           {responseKey}; if no such list exists, create it as an empty list.
         * Append all items in {fragmentGroup} to {groupForResponseKey}.
-    * If {selection} is an inline fragment:
+    * If {selection} is an {InlineFragment}:
       * Let {fragmentType} be the type condition on {selection}.
       * If {fragmentType} is not {null} and {doesFragmentTypeApply(objectType, fragmentType)} is false, continue
         with the next {selection} in {selectionSet}.
       * Let {fragmentSelectionSet} be the top-level selection set of {selection}.
-      * Let {fragmentGroupedFields} be the result of calling {CollectFields(objectType, fragmentSelectionSet)}.
-      * For each {fragmentGroup} in {fragmentGroupedFields}:
+      * Let {fragmentGroupedFieldSet} be the result of calling {CollectFields(objectType, fragmentSelectionSet, visitedFragments)}.
+      * For each {fragmentGroup} in {fragmentGroupedFieldSet}:
         * Let {responseKey} be the response key shared by all fields in {fragmentGroup}
         * Let {groupForResponseKey} be the list in {groupedFields} for
           {responseKey}; if no such list exists, create it as an empty list.
@@ -112,8 +112,10 @@ it should be evaluated normally.
 
 ## Evaluating a grouped field set
 
-The result of evaluating a grouped field set will be an unordered map. There
-will be an entry in this map for every item in the grouped field set.
+The result of evaluating a grouped field set will be an ordered map. For each
+item in the grouped field set, an entry is added to the resulting ordered map,
+where the key is the response key shared by all fields for that entry, and the
+value is the result of evaluating those fields.
 
 ### Field entries
 

spec/Section 7 -- Response.md

@@ -20,6 +20,10 @@ representations of the following four primitives:
  * String
  * Null
 
+Serialization formats which only support an ordered map (such as JSON) must
+preserve ordering as it is defined by query execution. Serialization formats
+which only support an unordered map may omit this ordering information.
+
 A serialization format may support the following primitives, however, strings
 may be used as a substitute for those primitives.
 
@@ -52,13 +56,13 @@ the following JSON concepts:
 
 A response to a GraphQL operation must be a map.
 
-If the operation included execution, the response map must contain an entry
+If the operation included execution, the response map must contain a first entry
 with key `data`. The value of this entry is described in the "Data" section. If
 the operation failed before execution, due to a syntax error, missing
 information, or validation error, this entry must not be present.
 
-If the operation encountered any errors, the response map must contain an entry
-with key `errors`. The value of this entry is described in the "Errors"
+If the operation encountered any errors, the response map must contain a next
+entry with key `errors`. The value of this entry is described in the "Errors"
 section. If the operation completed without encountering any errors, this entry
 must not be present.