Update docs & CHANGELOG after #795

CHANGELOG.md

@@ -9,6 +9,11 @@ This project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html
 
 ## Unreleased - xxxx-xx-xx
 
+### New Features
+
+- `Enum`s can now opt out of exhaustiveness checking with the `non_exhaustive`
+  attribute
+
 ## v3.3.3 - 2024-01-09
 
 ### Bug Fixes

cynic-book/src/derives/enums.md

@@ -24,6 +24,15 @@ smoothly, Cynic matches rust variants up to their equivalent
 specifying a `rename_all = "None"` attribute, or customised alternative
 `rename_all` values or individual `rename` attributes on the variants.
 
+#### Exhaustiveness Checking
+
+By default, cynic checks the exhuastiveness of `Enum`s - you should provide a
+variant for each enum value in the GraphQL schema.  You can also provide a `fallback` variant to provide forwards compatability - if the server adds new enum values they'll be caught by this variant.
+
+You can opt-out of this exhaustiveness using the `#[cynic(non_exhaustive)]`
+attribute.  When this is present exhaustiveness is not checked, and the
+fallback variant is used for all the variants missing from the selection.
+
 #### Enum Attributes
 
 An Enum can be configured with several attributes on the enum itself:
@@ -42,6 +51,9 @@ An Enum can be configured with several attributes on the enum itself:
 - `schema_module` tells cynic where to find your schema module. This is
   optional and should only be needed if your schema module is not in scope or
   is named something other than `schema`.
+- `non_exhaustive` can be provided to mark an enum as non-exhaustive.  Such
+  enums are required to have a fallback variant, but not required to have
+  a variant for each value in the schema.
 
 <!-- TODO: list of the rename rules, possibly pulled from codegen docs -->