fix(nitrogen): prevent exponential traversal and support cyclic struct references by puckey · Pull Request #1232 · mrousavy/nitro

puckey · 2026-03-02T11:26:28Z

Two related fixes for nitrogen code generation with complex/self-referential struct types:

1. Prevent exponential type re-traversal (fixes #1079)

getRequiredImports() and getExtraFiles() in SwiftCxxBridgedType and KotlinCxxBridgedType were visiting the same types exponentially many times for interconnected struct graphs
Added per-call-tree visited sets (as default parameters) to skip already-visited types
Tested with a 7-struct Gallery graph that previously caused stack overflow

2. Support self-referential/cyclic struct types (fixes #1070)

Structs referencing themselves through reference types (arrays, callbacks, promises, records) caused infinite recursion during code generation
Break the cycle by tracking structs being initialized and using lazy property resolution in StructType — when a struct is encountered while it's already being processed, the cached instance is returned instead of recursing infinitely
Simpler approach to the problem addressed in fix(nitrogen): handle cyclic struct references #1074, per mrousavy's feedback about reducing complexity

Test plan

Added a 7-struct Gallery graph that triggers exponential traversal
Added a self-referential TreeNode struct (children: TreeNode[], onChange?: (node: TreeNode) => void)
bun run specs in packages/react-native-nitro-test/ succeeds without stack overflow
Generated C++ uses forward declarations and reference types correctly

vercel · 2026-03-02T11:26:34Z

@puckey is attempting to deploy a commit to the Margelo Team on Vercel.

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mrousavy · 2026-03-02T12:08:09Z

+  using namespace facebook;
+
+  // Forward declarations for cyclic dependencies
+${forwardDeclarations}


That should be move to the right and used with indent(...)

Fixed — using getForwardDeclaration() now handles the formatting.

mrousavy · 2026-03-02T12:08:25Z

+
+    // Forward declarations for cyclic function types
+    const forwardDeclarations = Array.from(cyclicNames)
+      .map((name) => `  struct J${name};`)


We have a utility for that - getForwardDeclaration I think.

Done — switched to getForwardDeclaration() utility in both KotlinStruct.ts and KotlinFunction.ts.

mrousavy · 2026-03-02T12:08:42Z

+  using namespace facebook;
+
+  // Forward declarations for cyclic dependencies
+${forwardDeclarations}


That also shouldn't be inside the namespace. What about forward declarations from external packages?

Fixed — forward declarations are now placed before the namespace block using getForwardDeclaration(), which wraps each declaration in its own namespace. Applied to both KotlinStruct.ts and KotlinFunction.ts.

mrousavy · 2026-03-02T12:09:36Z

-#include <NitroModules/JPromise.hpp>
-#include <NitroModules/JInstant.hpp>
-#include <NitroModules/JAnyMap.hpp>
+


That doesn't look correct. We definitely use those types, so we have to either forward-declare or import them. Ideally forward declare here, and remove the whole bodies here, and move it into a .cpp file with an import. But thats for the future, for now import should work.

Fixed — this was caused by the visited sets being module-level, so types visited while generating one file were skipped for all subsequent files in the same codegen run. Changed to per-call-tree visited sets (passed as default parameters) so each file generation starts fresh.

mrousavy · 2026-03-02T12:10:10Z

How will a struct that references itself work? This is not possible in C++ and Swift, as it has an infinite size

puckey · 2026-03-02T13:20:12Z

Self-references are only allowed through reference types (arrays, callbacks, promises, records) — these use heap indirection so the struct size stays finite. Direct self-references like next: TreeNode throw an error at codegen time suggesting to wrap in an array or callback.

puckey · 2026-03-02T13:25:07Z

Verified that direct self-references are rejected at codegen time:

❌ Failed to generate spec for TestObjectCpp! Error: Cyclic struct reference detected:
   "TreeNode" references itself directly. Structs cannot have direct cyclic references
   because they are value types with fixed size in C++ and Swift.
   See: https://nitro.margelo.com/docs/types/custom-structs#direct-cyclic-references-are-not-supported

…es (PR #1232) Replace vendored codegen with upstream nitrogen from mrousavy/nitro#1232, adding support for cyclic/self-referential struct types and preventing exponential type re-traversal.

Upgrade to Nitro Modules 0.35.0 which fixes a critical memory leak in Kotlin HybridObjects and removes the deprecated `updateNative` API. - nitrogen: ^0.31.1 → ^0.35.0 - react-native-nitro-modules: ^0.31.1 → ^0.35.0 (devDeps, peerDeps, example, example-expo) - Use --stack-size=65536 for nitrogen scripts to work around upstream exponential type traversal bug (mrousavy/nitro#1232) Closes #3159 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

….0 (#3162) ## Summary - Upgrade `nitrogen` and `react-native-nitro-modules` from `^0.31.1` to `^0.35.0` - Fixes build failure with `react-native-nitro-modules` 0.35.0 (`Unresolved reference 'updateNative'`) - Adds `--stack-size=65536` workaround for nitrogen codegen exponential type traversal bug ## Background Nitro Modules [v0.35.0](https://github.com/mrousavy/nitro/releases/tag/v0.35.0) includes a **breaking change** for Kotlin HybridObjects — the `updateNative()` API was removed to fix a critical memory leak. This caused the build failure reported in #3159. ### Why `--stack-size=65536`? Nitrogen 0.35.0 has a known [exponential type traversal bug](mrousavy/nitro#1232) where `getReferencedTypes()` revisits the same types repeatedly without a visited set. For large specs like ours (40+ methods, complex nested structs), this exceeds the default Node.js stack size. Increasing the stack size is a safe workaround until the upstream fix ([mrousavy/nitro#1232](mrousavy/nitro#1232)) is merged — at which point we can revert to the standard `nitrogen` CLI. ## Changes ### Dependencies - `nitrogen`: `^0.31.1` → `^0.35.0` - `react-native-nitro-modules`: `^0.31.1` → `^0.35.0` (root devDeps, peerDeps, example, example-expo) ### Scripts (`package.json`) - `nitrogen` and `specs` scripts now use `node --stack-size=65536 node_modules/nitrogen/lib/index.js` instead of bare `nitrogen` CLI ### Generated files (`nitrogen/generated/` — gitignored) - Regenerated with nitrogen 0.35.0 - `HybridRnIapSpec.kt`: `updateNative()` removed (fixes #3159) - JNI initialization updated internally to `facebook::jni::initialize()` pattern ## Test plan - [x] `yarn typecheck` passes - [x] `yarn lint` passes - [x] `yarn test` — 251 tests passed - [x] `yarn specs` — generates 1/1 HybridObject successfully Closes #3159 🤖 Generated with [Claude Code](https://claude.ai/code)  ## Summary by CodeRabbit * **Chores** * Bumped react-native-nitro-modules and related tooling to ^0.35.0 and updated CLI execution scripts. * **Improvements** * More consistent, null-safe in-app purchase data across iOS and Android with standardized init/connection flows, improved serialization, and a minimal promoted-product fallback. * Public API shapes now consistently use variant-wrapped optional values for more predictable behavior. * **Bug Fixes** * Safer purchase error handling that preserves original error details.  --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

puckey · 2026-03-20T09:12:52Z

Another library running into this issue is forced to solve it by increasing their node stack size: hyochan/react-native-iap@ed55e2a

Why --stack-size=65536?

Nitrogen 0.35.0 has a known exponential type traversal
bug where
getReferencedTypes() revisits the same types repeatedly without a
visited set. For large specs like ours (40+ methods, complex nested
structs), this exceeds the default Node.js stack size. Increasing the
stack size is a safe workaround until the upstream fix
(#1232) is
merged — at which point we can revert to the standard nitrogen CLI.

mrousavy · 2026-03-20T09:37:28Z

Okay thanks, I will give this another look.

A deep/wide struct graph (7 interconnected types) where multiple structs reference the same shared types from many paths. Without a fix, nitrogen code generation stack-overflows because shared types get re-traversed from every path in the type graph (mrousavy#1079). Note: `bun run specs` will fail on this commit — the fix follows in the next commit.

`getRequiredImports()` and `getExtraFiles()` in nitrogen's `SwiftCxxBridgedType` (the TypeScript class that generates the Swift <-> C++ bridge code) have no protection against re-traversing the same type from multiple paths in the type graph, causing exponential blowup and stack overflow for projects with many interconnected struct types. mrousavy#1247 added a visited-set guard to the equivalent `KotlinCxxBridgedType`; this applies the same per-call-tree visited-set guard to `SwiftCxxBridgedType`. The visited sets also act as the cycle guard for cyclic struct references later in this branch. Fixes mrousavy#1079

Adds a TreeNode struct that references itself through an array (children: TreeNode[]) and a callback (onChange?: (node: TreeNode) => void), plus a bounceTreeNode method on SharedTestObjectProps. Note: `bun run specs` will stack-overflow on this commit — the fix follows in the next commit.

Structs that reference themselves through reference types (arrays, callbacks, promises, records) previously caused a stack overflow during code generation. Break the cycle by tracking structs being initialized and using lazy property resolution in StructType. When a struct is encountered while it's already being processed, the cached instance is returned instead of recursing infinitely. Follows up on PR mrousavy#1074 with a simpler approach per mrousavy's feedback about reducing complexity. Fixes mrousavy#1070

The cyclic initialization fallback in StructType.getRequiredImports used the bare struct name (e.g. "TreeNode") instead of the filename ("TreeNode.hpp"), causing a self-include that slipped past the CppStruct filter. Harmless due to #pragma once, but unnecessary.

Address review feedback: - Use the existing `getForwardDeclaration()` utility instead of manually constructing forward declaration strings - Move forward declarations before the namespace block, matching the pattern used in CppStruct.ts

puckey mentioned this pull request Mar 2, 2026

fix(nitrogen): handle cyclic struct references #1074

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puckey force-pushed the fix/cyclic-struct-references branch from 738f160 to 75008ff Compare March 2, 2026 11:42

mrousavy reviewed Mar 2, 2026

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puckey mentioned this pull request Mar 2, 2026

fix: prevent exponential type re-traversal in BridgedType visitors #1231

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puckey changed the title ~~fix(nitrogen): support cyclic/self-referential struct types~~ fix(nitrogen): prevent exponential traversal and support cyclic struct references Mar 2, 2026

puckey force-pushed the fix/cyclic-struct-references branch from 75008ff to b23fa05 Compare March 2, 2026 13:19

puckey force-pushed the fix/cyclic-struct-references branch from d95a14e to 49faf43 Compare March 4, 2026 14:37

hyochan mentioned this pull request Mar 9, 2026

chore(deps): upgrade nitrogen and react-native-nitro-modules to ^0.35.0 hyochan/react-native-iap#3162

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puckey added 9 commits June 12, 2026 11:49

docs: add cyclic struct references section and improve error message

4bc92b0

test: implement bounceGallery and bounceTreeNode in test HybridObjects

c5ddae7

chore: regenerate specs after rebase onto main

ec3cd05

puckey force-pushed the fix/cyclic-struct-references branch from 49faf43 to ec3cd05 Compare June 12, 2026 10:08

puckey mentioned this pull request Jun 12, 2026

fix: Prevent exponential type re-traversal in SwiftCxxBridgedType #1387

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mrousavy commented Mar 2, 2026

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puckey commented Mar 20, 2026

Why --stack-size=65536?

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mrousavy commented Mar 20, 2026

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puckey commented Mar 2, 2026 •

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Why `--stack-size=65536`?