relay-transforms: optionally use native gql fragment spreads for unmasked fragments

When Relay encountered a fragment spread with the `@relay(mask: false)`
directive, it would previously inline that fragment text into the query
itself. This is completely valid and equivalent to a native GraphQL
fragment spread. That inlining can dramatically increase the size of
serialize for a query with multiple fragments. Such repetition compresses
extremely well, but clients and servers still pay the cost of having
uncompressed strings in-memory (plus compress/decompress time).

Allow relay users to opt out of fragment inlining for
`@relay(mask: false)` fragment spreads in queries, using a native
GraphQL fragment spread. The reader AST and type generation are not
affected so there's no impact to the relay runtime.

Author: sjbarag

compiler/crates/common/src/feature_flags.rs

@@ -167,6 +167,14 @@ pub struct FeatureFlags {
     /// across a number of diffs.
     #[serde(default)]
     pub legacy_include_path_in_required_reader_nodes: FeatureFlag,
+
+    /// Produce native GraphQL fragment spreads when spreading a fragment with
+    /// @relay(mask: false) into a query, instead of inlining the contents of
+    /// that fragment for each use. This significantly reduces the uncompressed
+    /// size of query text when several mask:false fragment spreads are present,
+    /// but has no impact on masking behavior.
+    #[serde(default)]
+    pub use_native_fragment_spreads_for_unmasked_fragments: bool,
 }
 
 #[derive(Debug, Deserialize, Clone, Serialize, Default, JsonSchema)]

compiler/crates/relay-compiler/relay-compiler-config-schema.json

@@ -829,6 +829,11 @@
             }
           ]
         },
+        "use_native_fragment_spreads_for_unmasked_fragments": {
+          "description": "Produce native GraphQL fragment spreads when spreading a fragment with @relay(mask: false) into a query, instead of inlining the contents of that fragment for each use. This significantly reduces the uncompressed size of query text when several mask:false fragment spreads are present, but has no impact on masking behavior.",
+          "default": false,
+          "type": "boolean"
+        },
         "use_reader_module_imports": {
           "description": "Generate the `moduleImports` field in the Reader AST.",
           "default": {
@@ -1067,6 +1072,7 @@
             "text_artifacts": {
               "kind": "disabled"
             },
+            "use_native_fragment_spreads_for_unmasked_fragments": false,
             "use_reader_module_imports": {
               "kind": "disabled"
             }