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Fix integer overflow in getCrossProductUnionSize causing hang on large template literal types #3929

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Fix integer overflow in getCrossProductUnionSize causing hang on large template literal types #3929

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27bbd7f
Initial plan
Copilot May 16, 2026
d7c783d
Fix integer overflow in getCrossProductUnionSize causing hang on larg…
Copilot May 16, 2026
a446575
Use math.MaxInt and add comment for overflow guard in getCrossProduct…
Copilot May 16, 2026
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9 changes: 8 additions & 1 deletion internal/checker/checker.go
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Original file line number Diff line number Diff line change
Expand Up @@ -26447,7 +26447,14 @@ func (c *Checker) getCrossProductUnionSize(types []*Type) int {
for _, t := range types {
switch {
case t.flags&TypeFlagsUnion != 0:
size *= len(t.Types())
n := len(t.Types())
// Cap the result to avoid integer overflow when computing the cross product of many large unions.
// In TypeScript, number overflow produces Infinity which naturally exceeds the limit check;
// in Go, we must guard against int wrapping to zero or negative.
if n > 0 && size > math.MaxInt/n {
return math.MaxInt
}
size *= n
case t.flags&TypeFlagsNever != 0:
return 0
}
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10 changes: 10 additions & 0 deletions testdata/baselines/reference/compiler/templateLiteralTypeTooComplex.errors.txt
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@@ -0,0 +1,10 @@
templateLiteralTypeTooComplex.ts(3,10): error TS2590: Expression produces a union type that is too complex to represent.


==== templateLiteralTypeTooComplex.ts (1 errors) ====
// Large template literal types with combinatorial explosion should produce an error, not hang.
type N = 0 | 1 | 2 | 3;
type T = `${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}`;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!!! error TS2590: Expression produces a union type that is too complex to represent.

10 changes: 10 additions & 0 deletions testdata/baselines/reference/compiler/templateLiteralTypeTooComplex.js
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@@ -0,0 +1,10 @@
//// [tests/cases/compiler/templateLiteralTypeTooComplex.ts] ////

//// [templateLiteralTypeTooComplex.ts]
// Large template literal types with combinatorial explosion should produce an error, not hang.
type N = 0 | 1 | 2 | 3;
type T = `${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}`;


//// [templateLiteralTypeTooComplex.js]
"use strict";
59 changes: 59 additions & 0 deletions testdata/baselines/reference/compiler/templateLiteralTypeTooComplex.symbols
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@@ -0,0 +1,59 @@
//// [tests/cases/compiler/templateLiteralTypeTooComplex.ts] ////

=== templateLiteralTypeTooComplex.ts ===
// Large template literal types with combinatorial explosion should produce an error, not hang.
type N = 0 | 1 | 2 | 3;
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))

type T = `${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}`;
>T : Symbol(T, Decl(templateLiteralTypeTooComplex.ts, 1, 23))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))
>N : Symbol(N, Decl(templateLiteralTypeTooComplex.ts, 0, 0))

10 changes: 10 additions & 0 deletions testdata/baselines/reference/compiler/templateLiteralTypeTooComplex.types
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
//// [tests/cases/compiler/templateLiteralTypeTooComplex.ts] ////

=== templateLiteralTypeTooComplex.ts ===
// Large template literal types with combinatorial explosion should produce an error, not hang.
type N = 0 | 1 | 2 | 3;
>N : N

type T = `${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}`;
>T : any

5 changes: 5 additions & 0 deletions testdata/tests/cases/compiler/templateLiteralTypeTooComplex.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
// @strict: true

// Large template literal types with combinatorial explosion should produce an error, not hang.
type N = 0 | 1 | 2 | 3;
type T = `${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}${N}`;
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