relay-compiler: default feature flags are not added when missing featureFlags in config #5063
Description
Problem
Default feature flags are not added when featureFlags is not set; every feature flag is false.
With the recent release of v19:
https://relay.dev/blog/2025/04/02/relay-19/#alias-required-on-conditional-fragments
The enforce_fragment_alias_where_ambiguous feature flag has been set to true by default.
However, for a relay.config without featureFlags e.g.:
{
//...
"projects": {
"test": {
"customScalarTypes": {},
"enumModuleSuffix": ".test",
"schema": "packages/relay-test-utils-internal/testschema.graphql",
"language": "javascript"
}
}
}The default flags are not set, meaning enforce_fragment_alias_where_ambiguous is false.
Adding an empty featureFlags enables the default flags:
{
//...
"projects": {
"test": {
//...
"featureFlags": {}, <---------------- adding this enables default flags
}
}
}yields the same as:
{
//...
"projects": {
"test": {
//...
"featureFlags": {
"enforce_fragment_alias_where_ambiguous": {
"kind": "enabled"
}
}
}
}
}Repro on this branch:
https://github.com/ansemb/relay/blob/user/ansemb/feature-flag-repro
by adding an @include:
https://github.com/ansemb/relay/blob/user/ansemb/feature-flag-repro/compiler/test-project/src/App.js#L14
Toggling this line with featureFlags give different results:
https://github.com/ansemb/relay/blob/user/ansemb/feature-flag-repro/compiler/test-project/relay.config.json#L17
with the following (expected) error, when enforce_fragment_alias_where_ambiguous is enabled:
❯ ../target/release/relay compiler (base)
[INFO] Querying files to compile...
[INFO] [test] compiling...
[ERROR] Error in the project `test`: ✖ Expected `@alias` directive. Fragment spreads with (or within an inline fragment with) `@include` are conditionally fetched. Add `@alias` to this spread to expose the fragment reference as a nullable property.
compiler/test-project/src/App.js:14:10
13 │ ...Component_node
14 │ ...User_dataFragment @include(if: $includeUserBody)
│ ^^^^^^^^^^^^^^^^^
15 │ }
ℹ The condition is defined here:
compiler/test-project/src/App.js:14:28
13 │ ...Component_node
14 │ ...User_dataFragment @include(if: $includeUserBody)
│ ^^^^^^^^
15 │ }
[ERROR] Compilation failed.
[ERROR] Unable to run relay compiler. Error details:
Failed to build:
- Validation errors: 1 error(s) encountered above.
Expectation
The below configs should yield the same result.
No featureFlags:
{
//...
"projects": {
"test": {
"customScalarTypes": {},
"enumModuleSuffix": ".test",
"schema": "packages/relay-test-utils-internal/testschema.graphql",
"language": "javascript"
}
}
}Empty featureFlags:
{
//...
"projects": {
"test": {
"customScalarTypes": {},
"enumModuleSuffix": ".test",
"schema": "packages/relay-test-utils-internal/testschema.graphql",
"featureFlags": {},
"language": "javascript",
}
}
}