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fix(codegen): iteratively inline nested fragment spreads #426

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wax911 merged 2 commits into from
Jun 25, 2026
Merged

fix(codegen): iteratively inline nested fragment spreads #426

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3ac50c6
fix(codegen): iteratively inline nested fragment spreads
wax911 Jun 25, 2026
51e950c
chore(ide): update Gradle project modules and Kotlin version
wax911 Jun 25, 2026
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20 changes: 20 additions & 0 deletions .idea/gradle.xml
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3 changes: 2 additions & 1 deletion .idea/kotlinc.xml
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100 changes: 47 additions & 53 deletions ...gen-core/src/main/kotlin/co/anitrend/retrofit/graphql/codegen/resolve/FragmentResolver.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -88,79 +88,73 @@ class FragmentResolver {
* 2. Compute all transitively-reachable fragment names from the operation's
* direct fragment spreads, validating that every referenced fragment exists.
* 3. Detect cycles among the reachable fragments.
* 4. Transform: replace each [FragmentSpread] with an inline fragment.
* 5. Validate: no named fragment spreads remain (defensive invariant check).
* 4. Iteratively transform: replace each [FragmentSpread] with an inline
* fragment. Because the [AstTransformer] does not recursively visit the
* **children** of nodes inserted via [TreeTransformerUtil.changeNode], a
* single pass leaves nested fragment spreads unresolved. We therefore
* loop: after each pass we check whether any fragment spreads remain and,
* if so, re-transform the result. The loop exits when the invariant check
* passes.
* 5. Serialize the fully-resolved AST back to a GraphQL document string.
*/
private fun flattenFragments(
documentText: String,
fragmentDefinitions: Map<String, FragmentDefinition>,
): String {
val document = parser.parseDocument(documentText)

// Phase 1: Compute full transitive closure of reachable fragment names
val reachableNames = computeReachableFragments(document, fragmentDefinitions)
val firstDocument = parser.parseDocument(documentText)
val reachableNames = computeReachableFragments(firstDocument, fragmentDefinitions)
if (reachableNames.isEmpty()) return documentText

// Phase 2: Validate no cycles among reachable fragments
detectCycles(reachableNames, fragmentDefinitions)

// Phase 3: Inline fragments using AstTransformer
val relevantDefinitions = fragmentDefinitions.filterKeys { it in reachableNames }

// Phase 3-4: Iteratively inline fragments until no spreads remain.
// The AstTransformer does not recursively visit children of nodes
// inserted via changeNode, so nested spreads (e.g. ...MediaTitleFragment
// inside ...MediaCoreFragment) require multiple passes.
val transformer = AstTransformer()
val transformed =
transformer.transform(
document,
object : NodeVisitorStub() {
@Suppress("UNCHECKED_CAST")
override fun visitFragmentSpread(
node: FragmentSpread,
context: TraverserContext<graphql.language.Node<*>>,
): TraversalControl {
val definition =
relevantDefinitions[node.name]
?: return TraversalControl.CONTINUE
val spreadVisitor =
object : NodeVisitorStub() {
@Suppress("UNCHECKED_CAST")
override fun visitFragmentSpread(
node: FragmentSpread,
context: TraverserContext<graphql.language.Node<*>>,
): TraversalControl {
val definition =
relevantDefinitions[node.name]
?: return TraversalControl.CONTINUE

// Replace spread with an inline fragment that carries the definition's
// selection set and type condition, plus any directives (e.g. @include,
// @skip) from the original spread. The AstTransformer will continue
// traversing into the children of this new node, resolving any nested
// FragmentSpread references automatically.
val spreadDirectives: List<Directive> = node.directives
val inlineFragment =
InlineFragment.newInlineFragment()
.typeCondition(definition.typeCondition)
.selectionSet(definition.selectionSet)
.also { builder ->
if (spreadDirectives.isNotEmpty()) {
builder.directives(spreadDirectives)
}
val spreadDirectives: List<Directive> = node.directives
val inlineFragment =
InlineFragment.newInlineFragment()
.typeCondition(definition.typeCondition)
.selectionSet(definition.selectionSet)
.also { builder ->
if (spreadDirectives.isNotEmpty()) {
builder.directives(spreadDirectives)
}
.build()
}
.build()

return TreeTransformerUtil.changeNode(
context as TraverserContext<InlineFragment>,
inlineFragment,
)
}
},
)
return TreeTransformerUtil.changeNode(
context as TraverserContext<InlineFragment>,
inlineFragment,
)
}
}

// Phase 4: Defensive invariant check — no named fragment spreads should
// remain after inlining. This catches bugs where a fragment spread name
// was not found in relevantDefinitions (e.g. missing from transitive closure).
val remainingSpreads = collectSpreadNames(transformed)
if (remainingSpreads.isNotEmpty()) {
throw IllegalStateException(
"Incomplete fragment resolution: the following fragment spread(s) remain " +
"unresolved after inlining: ${remainingSpreads.joinToString(", ")}. " +
"Ensure all referenced fragment definitions are included in the " +
"fragment definitions map.",
)
}
var document = firstDocument
var remainingSpreads: Set<String>
do {
document = transformer.transform(document, spreadVisitor) as graphql.language.Document
remainingSpreads = collectSpreadNames(document)
} while (remainingSpreads.isNotEmpty())

// Serialize the transformed AST back to a GraphQL document string
return AstPrinter.printAst(transformed)
return AstPrinter.printAst(document)
}

/**
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