Unbounded memory consumption with recursive conditional types causes compilation OOM

まだ誰も着手していません。

## Steps to reproduce

npx tsgo the following.ts file:

```typescript
export type NumericProperty = "n1" | "n2" | "n3" | "n4" | "n5" | "n6" | "n7" | "n8" | "n9" | "n10" | "n11" | "n12" | "n13" | "n14" | "n15" | "n16" | "n17" | "n18" | "n19" | "n20" | "n21" | "n22" | "n23" | "n24" | "n25" | "n26" | "n27" | "n28" | "n29" | "n30" | "n31" | "n32" | "n33" | "n34" | "n35" | "n36" | "n37" | "n38" | "n39" | "n40" | "n41" | "n42" | "n43" | "n44" | "n45" | "n46" | "n47" | "n48" | "n49" | "n50" | "n51" | "n52" | "n53" | "n54" | "n55" | "n56" | "n57" | "n58" | "n59" | "n60" | "n61" | "n62" | "n63" | "n64" | "n65" | "n66" | "n67" | "n68" | "n69" | "n70" | "n71" | "n72" | "n73" | "n74" | "n75" | "n76" | "n77" | "n78" | "n79" | "n80" | "n81" | "n82" | "n83" | "n84" | "n85" | "n86" | "n87" | "n88" | "n89" | "n90" | "n91" | "n92" | "n93" | "n94" | "n95" | "n96" | "n97" | "n98" | "n99" | "n100";

export type StringProperty = "s1" | "s2" | "s3" | "s4" | "s5" | "s6" | "s7" | "s8" | "s9" | "s10" | "s11" | "s12" | "s13" | "s14" | "s15" | "s16" | "s17" | "s18" | "s19" | "s20" | "s21" | "s22" | "s23" | "s24" | "s25" | "s26" | "s27" | "s28" | "s29" | "s30" | "s31" | "s32" | "s33" | "s34" | "s35" | "s36" | "s37" | "s38" | "s39" | "s40" | "s41" | "s42" | "s43" | "s44" | "s45" | "s46" | "s47" | "s48" | "s49" | "s50" | "s51" | "s52" | "s53" | "s54" | "s55" | "s56" | "s57" | "s58" | "s59" | "s60" | "s61" | "s62" | "s63" | "s64" | "s65" | "s66" | "s67" | "s68" | "s69" | "s70" | "s71" | "s72" | "s73" | "s74" | "s75" | "s76" | "s77" | "s78" | "s79" | "s80" | "s81" | "s82" | "s83" | "s84" | "s85" | "s86" | "s87" | "s88" | "s89" | "s90" | "s91" | "s92" | "s93" | "s94" | "s95" | "s96" | "s97" | "s98" | "s99" | "s100";

type Seq = { _brand: "Seq" };

// `Branch` to connect Branch
type Branch = Seq & {
type: "Branch";
left1: L1;
left2: L2;
right1: R1;
right2: R2;
};

// `A` and `B` are the basic elements of the sequence.
type A = Seq & { type: "A" };
type B = Seq & { type: "B" };
type C = Seq & { type: "C" };
type D = Seq & { type: "D" };

// Recursively rewrite the entire sequence tree.
type Rewrite = T extends A
? Branch
: T extends B
? Branch
: T extends C
? Branch
: T extends D
? Branch
: T extends Branch
? Branch, Rewrite, Rewrite, Rewrite>
: never;

// `Nat` and `Succ`/`Zero` are used for type-level counting.
// Represents numbers at the type level.
type Nat = { _brand: "nat" };
type Zero = Nat & { type: "Zero" };
type Succ = Nat & { type: "Succ"; pred: N };

// Apply rewrite rules N times using recursive conditional types
// TypeScript has recursion depth limits, so large N values will fail
type ApplyRewrite = N extends Zero
? S // Base case: 0 iterations returns original
: N extends Succ // Recursive case: N = Succ(P)
? ApplyRewrite, P> // Apply one rewrite, then recurse with P
: never;

// Define a more complex type union calculation
type SeqUnion = T extends A
? StringProperty
: T extends B
? NumericProperty
: T extends C
? `${NumericProperty}${StringProperty}`
: T extends D
? `${StringProperty}${NumericProperty}`
: T extends Branch
? `${SeqUnion}${SeqUnion}` | `${SeqUnion}${SeqUnion}`
: never;

// trigger the compile-time evaluation.
type InitialState = A;

// Note: the following is harmful. Set iteration count to N=40.
// Complex binary tree
// Result: Compilation bomb! Compilation leads to OOM, takes a very long time, and causes a Denial of Service.
type N40 = Succ>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>;

// Generate final result type.
type FinalState = ApplyRewrite;
type FinalUnion = SeqUnion;

const finalUnion = {} as FinalUnion;
console.log("Compilation succeeded! The final type is:", finalUnion);

```

## Behavior with `typescript@5.8`

The compilation fails gracefully with a standard Out of Memory (OOM) error. The Node.js runtime (V8 engine) enforces a default heap memory limit (typically ~4GB on 64-bit systems), which prevents the process from consuming all available system resources.

Result: The process terminates immediately, leaving the host operating system responsive.

Ref: https://v8.dev/blog/4gb-wasm-memory
https://stackoverflow.com/questions/79250132/how-does-node-v8-determine-its-max-heap-size

## Behavior with `tsgo`

The compiler exhibits unbounded memory consumption. Unlike the Node.js runtime, tsgo lacks a default heap ceiling. It continues to allocate memory until it exhausts both physical RAM and swap space.

Result: The host system hangs or freezes, rendering it unresponsive until the operating system's kernel OOM Killer forcibly terminates the process.

## My Point

Suggest evaluating mitigation strategies for this unbounded memory usage. If tsgo is intended for broader use (other than web), the current behavior risks stability. If tsgo targets only web, adopting a V8-like memory limit is an acceptable solution. This choice warrants careful consideration.

提供された TypeScript の例に対して npx tsgo を実行して報告された失敗を再現し、その後、メモリ動作を typescript@5.8 と比較します。ソースファイルやテストは指定されておらず、issue では緩和策も未決定のままです。完了には、メモリ使用量を制限するか、別の方法で制御するための合意された戦略と、このケースの回帰チェックが必要です。

索引モデルが issue の本文から書いたものです。