Performance regression for declaration emit of an oversized inferred type

🔎 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:

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.

Empieza ejecutando el repro.ts proporcionado con declaration emit y comparando Go tsc con el compilador de JavaScript mediante el comando time mostrado. Después, inspecciona la ruta de declaration emit alrededor de NodeBuilder, serializedTypes y DeepCloneNode. Se considera terminado cuando el compilador de Go sigue informando de TS7056, pero evita el uso adicional de memoria y la ralentización indicados.