Add feature flag and codegen for ReadonlyArray

Reviewed By: captbaritone

Differential Revision: D86834414

fbshipit-source-id: 06eab97694a4fa140e951e03a722fd5ac4d19869

Author: marcoww6

compiler/crates/common/src/feature_flags.rs

@@ -186,6 +186,11 @@ pub struct FeatureFlags {
     /// be null in normal operation).
     #[serde(default)]
     pub disallow_required_action_throw_on_semantically_nullable_fields: FeatureFlag,
+
+    /// Use ReadonlyArray<T> instead of $ReadOnlyArray<T> for Flow typegen.
+    /// This enables gradual rollout of the new array type across files.
+    #[serde(default)]
+    pub readonly_array_for_flow: FeatureFlag,
 }
 
 impl Default for FeatureFlags {
@@ -218,6 +223,7 @@ impl Default for FeatureFlags {
             disable_deduping_common_structures_in_artifacts: Default::default(),
             legacy_include_path_in_required_reader_nodes: Default::default(),
             disallow_required_action_throw_on_semantically_nullable_fields: Default::default(),
+            readonly_array_for_flow: Default::default(),
 
             // enabled-by-default
             enforce_fragment_alias_where_ambiguous: FeatureFlag::Enabled,

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

@@ -694,6 +694,13 @@
           "type": "boolean",
           "default": false
         },
+        "readonly_array_for_flow": {
+          "description": "Use ReadonlyArray<T> instead of $ReadOnlyArray<T> for Flow typegen.\nThis enables gradual rollout of the new array type across files.",
+          "$ref": "#/$defs/FeatureFlag",
+          "default": {
+            "kind": "disabled"
+          }
+        },
         "relay_resolver_enable_interface_output_type": {
           "description": "Enable returning interfaces from Relay Resolvers without @outputType",
           "$ref": "#/$defs/FeatureFlag",
@@ -930,6 +937,9 @@
               "kind": "disabled"
             },
             "prefer_fetchable_in_refetch_queries": false,
+            "readonly_array_for_flow": {
+              "kind": "disabled"
+            },
             "relay_resolver_enable_interface_output_type": {
               "kind": "disabled"
             },

compiler/crates/relay-typegen/src/flow.rs

@@ -20,6 +20,7 @@ use crate::writer::Writer;
 pub struct FlowPrinter {
     result: String,
     indentation: usize,
+    use_readonly_array_rollout: bool,
 }
 
 impl Write for FlowPrinter {
@@ -152,10 +153,11 @@ impl Writer for FlowPrinter {
 }
 
 impl FlowPrinter {
-    pub fn new() -> Self {
+    pub fn new(use_readonly_array: impl Into<Option<bool>>) -> Self {
         Self {
             result: String::new(),
             indentation: 0,
+            use_readonly_array_rollout: use_readonly_array.into().unwrap_or(false),
         }
     }
 
@@ -198,7 +200,11 @@ impl FlowPrinter {
     }
 
     fn write_read_only_array(&mut self, of_type: &AST) -> FmtResult {
-        write!(&mut self.result, "$ReadOnlyArray<")?;
+        if self.use_readonly_array_rollout {
+            write!(&mut self.result, "ReadonlyArray<")?;
+        } else {
+            write!(&mut self.result, "$ReadOnlyArray<")?;
+        }
         self.write(of_type)?;
         write!(&mut self.result, ">")
     }
@@ -392,7 +398,7 @@ mod tests {
     use crate::writer::SortedASTList;
 
     fn print_type(ast: &AST) -> String {
-        let mut printer = Box::new(FlowPrinter::new());
+        let mut printer = Box::new(FlowPrinter::new(false));
         printer.write(ast).unwrap();
         printer.into_string()
     }
@@ -595,7 +601,7 @@ mod tests {
 
     #[test]
     fn import_type() {
-        let mut printer = Box::new(FlowPrinter::new());
+        let mut printer = Box::new(FlowPrinter::new(false));
         printer.write_import_type(&["A", "B"], "module").unwrap();
         assert_eq!(
             printer.into_string(),
@@ -605,7 +611,7 @@ mod tests {
 
     #[test]
     fn import_module() {
-        let mut printer = Box::new(FlowPrinter::new());
+        let mut printer = Box::new(FlowPrinter::new(false));
         printer.write_import_module_default("A", "module").unwrap();
         assert_eq!(printer.into_string(), "import A from \"module\";\n");
     }

compiler/crates/relay-typegen/src/lib.rs

@@ -160,7 +160,11 @@ fn generate_fragment_type_exports_section_impl(
             is_extra_artifact_branch_module,
         },
     );
-    let mut writer = new_writer_from_config(&project_config.typegen_config);
+    let use_readonly_array = project_config
+        .feature_flags
+        .readonly_array_for_flow
+        .is_enabled_for(fragment_definition.name.item.0);
+    let mut writer = new_writer_from_config(&project_config.typegen_config, use_readonly_array);
     write_fragment_type_exports_section(&typegen_context, fragment_definition, &mut writer)
         .unwrap();
     writer.into_string()
@@ -186,7 +190,11 @@ pub fn generate_named_validator_export(
             is_extra_artifact_branch_module: false,
         },
     );
-    let mut writer = new_writer_from_config(&project_config.typegen_config);
+    let use_readonly_array = project_config
+        .feature_flags
+        .readonly_array_for_flow
+        .is_enabled_for(fragment_definition.name.item.0);
+    let mut writer = new_writer_from_config(&project_config.typegen_config, use_readonly_array);
     write_validator_function(&typegen_context, fragment_definition, &mut writer).unwrap();
     let validator_function_body = writer.into_string();
 
@@ -222,7 +230,11 @@ pub fn generate_operation_type_exports_section(
             is_extra_artifact_branch_module: false,
         },
     );
-    let mut writer = new_writer_from_config(&project_config.typegen_config);
+    let use_readonly_array = project_config
+        .feature_flags
+        .readonly_array_for_flow
+        .is_enabled_for(typegen_operation.name.item.0);
+    let mut writer = new_writer_from_config(&project_config.typegen_config, use_readonly_array);
     write_operation_type_exports_section(
         &typegen_context,
         typegen_operation,
@@ -259,7 +271,11 @@ pub fn generate_split_operation_type_exports_section(
             is_extra_artifact_branch_module: false,
         },
     );
-    let mut writer = new_writer_from_config(&project_config.typegen_config);
+    let use_readonly_array = project_config
+        .feature_flags
+        .readonly_array_for_flow
+        .is_enabled_for(typegen_operation.name.item.0);
+    let mut writer = new_writer_from_config(&project_config.typegen_config, use_readonly_array);
 
     write_split_operation_type_exports_section(
         &typegen_context,

compiler/crates/relay-typegen/src/writer.rs

@@ -387,10 +387,13 @@ pub trait Writer: Write {
     fn write_any_type_definition(&mut self, name: &str) -> FmtResult;
 }
 
-pub(crate) fn new_writer_from_config(config: &TypegenConfig) -> Box<dyn Writer> {
+pub(crate) fn new_writer_from_config(
+    config: &TypegenConfig,
+    use_readonly_array_for_flow: bool,
+) -> Box<dyn Writer> {
     match config.language {
         TypegenLanguage::JavaScript => Box::<JavaScriptPrinter>::default(),
-        TypegenLanguage::Flow => Box::new(FlowPrinter::new()),
+        TypegenLanguage::Flow => Box::new(FlowPrinter::new(use_readonly_array_for_flow)),
         TypegenLanguage::TypeScript => Box::new(TypeScriptPrinter::new(config)),
     }
 }