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Performance regression for declaration emit of an oversized inferred type #63966
Description
🔎 Search Terms
TS7056 memory, declaration emit OOM, "inferred type of this node exceeds the maximum length", DeepCloneNode serializedTypes, NodeBuilder declaration emit memory, typescript-go TS7056 RSS
🕗 Version & Regression Information
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about declaration emit and large inferred types
- Reproduced on 7.1.0-dev (
main,./built/local/tsc) vs TypeScript 6.0.3 (./node_modules/typescript/bin/tsc). Both report the same TS7056 and emit no.d.ts. The Go compiler uses ~6× the memory and is 5.8x slower.
┌──────────────────────┬──────────┬────────┬──────────────────┐
│ version │ peak RSS │ wall │ result │
├──────────────────────┼──────────┼────────┼──────────────────┤
│ 5.9.3 │ 0.51 GB │ 0.97 s │ TS7056, no .d.ts │
├──────────────────────┼──────────┼────────┼──────────────────┤
│ 6.0.3 │ 0.41 GB │ 0.66 s │ TS7056, no .d.ts │
├──────────────────────┼──────────┼────────┼──────────────────┤
│ 7.0.0-dev.20260707.2 │ 2.38 GB │ 3.68 s │ TS7056, no .d.ts │
├──────────────────────┼──────────┼────────┼──────────────────┤
│ 7.0.1-rc │ 2.25 GB │ 3.51 s │ TS7056, no .d.ts │
├──────────────────────┼──────────┼────────┼──────────────────┤
│ 7.0.2 │ 2.25 GB │ 3.49 s │ TS7056, no .d.ts │
├──────────────────────┼──────────┼────────┼──────────────────┤
│ main 7.1.0-dev │ 2.42 GB │ 3.41 s │ TS7056, no .d.ts │
└──────────────────────┴──────────┴────────┴──────────────────┘
⏯ Playground Link
N/A
💻 Code
let x0 = { v: 1 };
let x1 = { a: x0, b: x0, c: x0 };
let x2 = { a: x1, b: x1, c: x1 };
let x3 = { a: x2, b: x2, c: x2 };
let x4 = { a: x3, b: x3, c: x3 };
let x5 = { a: x4, b: x4, c: x4 };
let x6 = { a: x5, b: x5, c: x5 };
let x7 = { a: x6, b: x6, c: x6 };
let x8 = { a: x7, b: x7, c: x7 };
let x9 = { a: x8, b: x8, c: x8 };
let x10 = { a: x9, b: x9, c: x9 };
let x11 = { a: x10, b: x10, c: x10 };
let x12 = { a: x11, b: x11, c: x11 };
let x13 = { a: x12, b: x12, c: x12 };
export const y = x13;/usr/bin/time -l tsc --declaration repro.ts🙁 Actual behavior
Both compilers:
repro.ts(15,14): error TS7056: The inferred type of this node exceeds the maximum length the compiler will serialize. An explicit type annotation is needed.
Measured on macOS with /usr/bin/time -l:
| compiler | peak RSS | wall |
|---|---|---|
Go tsc 7.1.0-dev |
2.48 GB | 3.5 s |
JS tsc 6.0.3 |
0.41 GB | 0.6 s |
In a limited environment, or with a larger repro, this will cause the process to OOM.
🙂 Expected behavior
Go tsc should report the same TS7056 error without using extra memory and being slower.
Additional information about the issue
Disclosure: This memory issue was found with a differential memory harness (Go tsc vs JS tsc 6.0.3) and AI assistance (Kimi K3). Verified by hand against TypeScript 7.1.0-dev (main) and TypeScript 6.0.3.
Activity
yunasora commentedon Aug 23, 2026
Hi, I’d like to work on this issue. I can reproduce the declaration emit performance regression and investigate the
tsgonode builder/cache path, particularly the repeated AST cloning aroundDeepCloneNode. I’m happy to add a focused regression test and benchmark the fix against the current behavior. If this issue is still available, could you please assign it to me? I’ll share progress and discuss the approach before submitting a PR.jakebailey commentedon Aug 24, 2026
Did you have an actual project which hit this, or did you just find this with an LLM looking at the code?
daniellockyer commentedon Aug 24, 2026
This repro was found via an LLM but I'm trying to improve memory usage of tsc/tsgo in general. I've got a few other bugs incoming that I can directly link to a project (but cannot provide the source code for, so I need to find a minimal public repro anyway)