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Stop unbounded memory growth after type complexity limits are hit #65308

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c7bc2c0
Stop unbounded memory growth after type complexity limits are hit
1-DARK Nov 4, 2026
4595875
Add templateLiteralComplexityLimit compiler test
1-DARK Nov 4, 2026
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41 changes: 38 additions & 3 deletions tsc/internal/checker/checker.go
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Expand Up @@ -605,6 +605,7 @@ type Checker struct {
SignatureCount uint32
TotalInstantiationCount uint32
instantiationCount uint32
instantiationLimitReportedNode *ast.Node // node for which the instantiation count limit error was already reported
memberLayoutCount uint32
instantiationStack []*Type
conditionalConstraintDepth uint32
Expand Down Expand Up @@ -22760,6 +22761,9 @@ func (c *Checker) symbolIsValueEx(symbol *ast.Symbol, includeTypeOnlyMembers boo
c.getSymbolFlagsEx(symbol, !includeTypeOnlyMembers, false /*excludeLocalMeanings*/)&ast.SymbolFlagsValue != 0
}

// The maximum number of type instantiations performed for a single statement or expression.
const maxInstantiationCount = 5_000_000

func (c *Checker) instantiateType(t *Type, m *TypeMapper) *Type {
return c.instantiateTypeWithAlias(t, m, nil /*alias*/)
}
Expand All @@ -22771,13 +22775,21 @@ func (c *Checker) instantiateTypeWithAlias(t *Type, m *TypeMapper, alias *TypeAl
if t == nil || m == nil || !(c.couldContainTypeVariables(t) || (t.alias != nil && len(t.alias.typeArguments) > 0 && core.Some(t.alias.typeArguments, c.couldContainTypeVariables))) {
return t
}
if len(c.instantiationStack) == 100 || c.instantiationCount >= 5_000_000 {
if len(c.instantiationStack) == 100 || c.instantiationCount >= maxInstantiationCount {
// We have reached 100 recursive type instantiations, or 5M type instantiations caused by the same statement
// or expression. There is a very high likelihood we're dealing with a combination of infinite generic types
// that perpetually generate new type identities, so we stop the recursion here by yielding the error type.
if tr := c.tracer; tr != nil {
tr.Instant(tracing.PhaseCheckTypes, "instantiateType_DepthLimit", map[string]any{"typeId": t.id, "instantiationDepth": len(c.instantiationStack), "instantiationCount": c.instantiationCount})
}
if c.instantiationCount >= maxInstantiationCount {
// Once the count limit is exceeded every further instantiation for this node hits the limit again.
// Report the error only once per node instead of allocating millions of identical diagnostics.
if c.instantiationLimitReportedNode == c.currentNode && c.currentNode != nil {
return c.errorType
}
c.instantiationLimitReportedNode = c.currentNode
}
circularTypeNames := c.getCircularTypeNames()
switch {
case len(circularTypeNames) == 1:
Expand Down Expand Up @@ -28308,6 +28320,14 @@ func (c *Checker) computeBaseConstraint(t *Type, stack []RecursionId) *Type {
}
return c.stringNumberSymbolType
case t.flags&TypeFlagsTemplateLiteral != 0:
if c.instantiationLimitReportedNode != nil && c.instantiationLimitReportedNode == c.currentNode && c.instantiationCount >= maxInstantiationCount {
// The instantiation limit has already been reported (TS2589) for the current node, and all further
// instantiations yield the error type. Expanding the constraint of this generic template literal type
// into a cross product of string literals would only allocate huge unions that can never be used.
// This is scoped to base constraint computation, which is only ever performed for generic types, so
// the error type is not cached for independently declared (non-generic) aliases.
return c.errorType
}
types := t.Types()
constraints := make([]*Type, 0, len(types))
for _, s := range types {
Expand Down Expand Up @@ -29956,9 +29976,24 @@ func (c *Checker) getTemplateLiteralType(texts []string, types []*Type) *Type {
if !c.checkCrossProductUnion(types) {
return c.errorType
}
return c.mapType(types[unionIndex], func(t *Type) *Type {
return c.getTemplateLiteralType(texts, core.ReplaceElement(types, unionIndex, t))
// Once a constituent produces an error (e.g. the cross product is too complex, or the template is too
// large), the whole result is the error type. Stop expanding the remaining constituents so we don't
// repeatedly redo the same work and report the same diagnostic for every combination.
failed := false
result := c.mapType(types[unionIndex], func(t *Type) *Type {
if failed {
return c.errorType
}
r := c.getTemplateLiteralType(texts, core.ReplaceElement(types, unionIndex, t))
if r == c.errorType {
failed = true
}
return r
})
if failed {
return c.errorType
}
return result
}
if slices.Contains(types, c.wildcardType) {
return c.wildcardType
Expand Down
31 changes: 31 additions & 0 deletions tsc/testdata/baselines/reference/compiler/templateLiteralComplexityLimit.errors.txt
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templateLiteralComplexityLimit.ts(5,15): error TS2590: Expression produces a union type that is too complex to represent.
templateLiteralComplexityLimit.ts(13,14): error TS2590: Expression produces a union type that is too complex to represent.
templateLiteralComplexityLimit.ts(18,5): error TS2322: Type '123' is not assignable to type '"x" | "y"'.


==== templateLiteralComplexityLimit.ts (3 errors) ====
// Once the cross product limit is reported, later expansions for the same node must bail out quickly.
type A = "a0" | "a1" | "a2" | "a3" | "a4" | "a5" | "a6" | "a7" | "a8" | "a9" | "a10" | "a11" | "a12" | "a13" | "a14" | "a15" | "a16" | "a17" | "a18" | "a19" | "a20" | "a21" | "a22" | "a23" | "a24" | "a25" | "a26" | "a27" | "a28" | "a29" | "a30" | "a31" | "a32" | "a33" | "a34" | "a35" | "a36" | "a37" | "a38" | "a39" | "a40" | "a41" | "a42" | "a43" | "a44" | "a45" | "a46" | "a47" | "a48" | "a49";
type B = "b0" | "b1" | "b2" | "b3" | "b4" | "b5" | "b6" | "b7" | "b8" | "b9" | "b10" | "b11" | "b12" | "b13" | "b14" | "b15" | "b16" | "b17" | "b18" | "b19" | "b20" | "b21" | "b22" | "b23" | "b24" | "b25" | "b26" | "b27" | "b28" | "b29" | "b30" | "b31" | "b32" | "b33" | "b34" | "b35" | "b36" | "b37" | "b38" | "b39" | "b40" | "b41" | "b42" | "b43" | "b44" | "b45" | "b46" | "b47" | "b48" | "b49";
type C = "c0" | "c1" | "c2" | "c3" | "c4" | "c5" | "c6" | "c7" | "c8" | "c9" | "c10" | "c11" | "c12" | "c13" | "c14" | "c15" | "c16" | "c17" | "c18" | "c19" | "c20" | "c21" | "c22" | "c23" | "c24" | "c25" | "c26" | "c27" | "c28" | "c29" | "c30" | "c31" | "c32" | "c33" | "c34" | "c35" | "c36" | "c37" | "c38" | "c39" | "c40" | "c41" | "c42" | "c43" | "c44" | "c45" | "c46" | "c47" | "c48" | "c49";
type TooBig = `${A}.${B}.${C}`;
~~~~~~~~~~~~~~~~
!!! error TS2590: Expression produces a union type that is too complex to represent.
declare function f<T extends string>(x: T): T;
f<TooBig>("a0.b0.c0");
type Nested = `${TooBig}.${A}`;
declare const n: Nested;
export const len = n.length;

// A limit error for one alias must not leak into unrelated aliases resolved in the same context.
type Force = Combined;
~~~~~~~~
!!! error TS2590: Expression produces a union type that is too complex to represent.
type Combined = TooBig2 | Small;
type TooBig2 = `${A}.${B}.${C}`;
type Small = `${"x" | "y"}`;
declare const force: Force;
let small: Small = 123;
~~~~~
!!! error TS2322: Type '123' is not assignable to type '"x" | "y"'.

72 changes: 72 additions & 0 deletions tsc/testdata/baselines/reference/compiler/templateLiteralComplexityLimit.symbols
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//// [tests/cases/compiler/templateLiteralComplexityLimit.ts] ////

=== templateLiteralComplexityLimit.ts ===
// Once the cross product limit is reported, later expansions for the same node must bail out quickly.
type A = "a0" | "a1" | "a2" | "a3" | "a4" | "a5" | "a6" | "a7" | "a8" | "a9" | "a10" | "a11" | "a12" | "a13" | "a14" | "a15" | "a16" | "a17" | "a18" | "a19" | "a20" | "a21" | "a22" | "a23" | "a24" | "a25" | "a26" | "a27" | "a28" | "a29" | "a30" | "a31" | "a32" | "a33" | "a34" | "a35" | "a36" | "a37" | "a38" | "a39" | "a40" | "a41" | "a42" | "a43" | "a44" | "a45" | "a46" | "a47" | "a48" | "a49";
>A : Symbol(A, Decl(templateLiteralComplexityLimit.ts, 0, 0))

type B = "b0" | "b1" | "b2" | "b3" | "b4" | "b5" | "b6" | "b7" | "b8" | "b9" | "b10" | "b11" | "b12" | "b13" | "b14" | "b15" | "b16" | "b17" | "b18" | "b19" | "b20" | "b21" | "b22" | "b23" | "b24" | "b25" | "b26" | "b27" | "b28" | "b29" | "b30" | "b31" | "b32" | "b33" | "b34" | "b35" | "b36" | "b37" | "b38" | "b39" | "b40" | "b41" | "b42" | "b43" | "b44" | "b45" | "b46" | "b47" | "b48" | "b49";
>B : Symbol(B, Decl(templateLiteralComplexityLimit.ts, 1, 397))

type C = "c0" | "c1" | "c2" | "c3" | "c4" | "c5" | "c6" | "c7" | "c8" | "c9" | "c10" | "c11" | "c12" | "c13" | "c14" | "c15" | "c16" | "c17" | "c18" | "c19" | "c20" | "c21" | "c22" | "c23" | "c24" | "c25" | "c26" | "c27" | "c28" | "c29" | "c30" | "c31" | "c32" | "c33" | "c34" | "c35" | "c36" | "c37" | "c38" | "c39" | "c40" | "c41" | "c42" | "c43" | "c44" | "c45" | "c46" | "c47" | "c48" | "c49";
>C : Symbol(C, Decl(templateLiteralComplexityLimit.ts, 2, 397))

type TooBig = `${A}.${B}.${C}`;
>TooBig : Symbol(TooBig, Decl(templateLiteralComplexityLimit.ts, 3, 397))
>A : Symbol(A, Decl(templateLiteralComplexityLimit.ts, 0, 0))
>B : Symbol(B, Decl(templateLiteralComplexityLimit.ts, 1, 397))
>C : Symbol(C, Decl(templateLiteralComplexityLimit.ts, 2, 397))

declare function f<T extends string>(x: T): T;
>f : Symbol(f, Decl(templateLiteralComplexityLimit.ts, 4, 31))
>T : Symbol(T, Decl(templateLiteralComplexityLimit.ts, 5, 19))
>x : Symbol(x, Decl(templateLiteralComplexityLimit.ts, 5, 37))
>T : Symbol(T, Decl(templateLiteralComplexityLimit.ts, 5, 19))
>T : Symbol(T, Decl(templateLiteralComplexityLimit.ts, 5, 19))

f<TooBig>("a0.b0.c0");
>f : Symbol(f, Decl(templateLiteralComplexityLimit.ts, 4, 31))
>TooBig : Symbol(TooBig, Decl(templateLiteralComplexityLimit.ts, 3, 397))

type Nested = `${TooBig}.${A}`;
>Nested : Symbol(Nested, Decl(templateLiteralComplexityLimit.ts, 6, 22))
>TooBig : Symbol(TooBig, Decl(templateLiteralComplexityLimit.ts, 3, 397))
>A : Symbol(A, Decl(templateLiteralComplexityLimit.ts, 0, 0))

declare const n: Nested;
>n : Symbol(n, Decl(templateLiteralComplexityLimit.ts, 8, 13))
>Nested : Symbol(Nested, Decl(templateLiteralComplexityLimit.ts, 6, 22))

export const len = n.length;
>len : Symbol(len, Decl(templateLiteralComplexityLimit.ts, 9, 12))
>n.length : Symbol(String.length, Decl(lib.es5.d.ts, --, --))
>n : Symbol(n, Decl(templateLiteralComplexityLimit.ts, 8, 13))
>length : Symbol(String.length, Decl(lib.es5.d.ts, --, --))

// A limit error for one alias must not leak into unrelated aliases resolved in the same context.
type Force = Combined;
>Force : Symbol(Force, Decl(templateLiteralComplexityLimit.ts, 9, 28))
>Combined : Symbol(Combined, Decl(templateLiteralComplexityLimit.ts, 12, 22))

type Combined = TooBig2 | Small;
>Combined : Symbol(Combined, Decl(templateLiteralComplexityLimit.ts, 12, 22))
>TooBig2 : Symbol(TooBig2, Decl(templateLiteralComplexityLimit.ts, 13, 32))
>Small : Symbol(Small, Decl(templateLiteralComplexityLimit.ts, 14, 32))

type TooBig2 = `${A}.${B}.${C}`;
>TooBig2 : Symbol(TooBig2, Decl(templateLiteralComplexityLimit.ts, 13, 32))
>A : Symbol(A, Decl(templateLiteralComplexityLimit.ts, 0, 0))
>B : Symbol(B, Decl(templateLiteralComplexityLimit.ts, 1, 397))
>C : Symbol(C, Decl(templateLiteralComplexityLimit.ts, 2, 397))

type Small = `${"x" | "y"}`;
>Small : Symbol(Small, Decl(templateLiteralComplexityLimit.ts, 14, 32))

declare const force: Force;
>force : Symbol(force, Decl(templateLiteralComplexityLimit.ts, 16, 13))
>Force : Symbol(Force, Decl(templateLiteralComplexityLimit.ts, 9, 28))

let small: Small = 123;
>small : Symbol(small, Decl(templateLiteralComplexityLimit.ts, 17, 3))
>Small : Symbol(Small, Decl(templateLiteralComplexityLimit.ts, 14, 32))

57 changes: 57 additions & 0 deletions tsc/testdata/baselines/reference/compiler/templateLiteralComplexityLimit.types
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//// [tests/cases/compiler/templateLiteralComplexityLimit.ts] ////

=== templateLiteralComplexityLimit.ts ===
// Once the cross product limit is reported, later expansions for the same node must bail out quickly.
type A = "a0" | "a1" | "a2" | "a3" | "a4" | "a5" | "a6" | "a7" | "a8" | "a9" | "a10" | "a11" | "a12" | "a13" | "a14" | "a15" | "a16" | "a17" | "a18" | "a19" | "a20" | "a21" | "a22" | "a23" | "a24" | "a25" | "a26" | "a27" | "a28" | "a29" | "a30" | "a31" | "a32" | "a33" | "a34" | "a35" | "a36" | "a37" | "a38" | "a39" | "a40" | "a41" | "a42" | "a43" | "a44" | "a45" | "a46" | "a47" | "a48" | "a49";
>A : A

type B = "b0" | "b1" | "b2" | "b3" | "b4" | "b5" | "b6" | "b7" | "b8" | "b9" | "b10" | "b11" | "b12" | "b13" | "b14" | "b15" | "b16" | "b17" | "b18" | "b19" | "b20" | "b21" | "b22" | "b23" | "b24" | "b25" | "b26" | "b27" | "b28" | "b29" | "b30" | "b31" | "b32" | "b33" | "b34" | "b35" | "b36" | "b37" | "b38" | "b39" | "b40" | "b41" | "b42" | "b43" | "b44" | "b45" | "b46" | "b47" | "b48" | "b49";
>B : B

type C = "c0" | "c1" | "c2" | "c3" | "c4" | "c5" | "c6" | "c7" | "c8" | "c9" | "c10" | "c11" | "c12" | "c13" | "c14" | "c15" | "c16" | "c17" | "c18" | "c19" | "c20" | "c21" | "c22" | "c23" | "c24" | "c25" | "c26" | "c27" | "c28" | "c29" | "c30" | "c31" | "c32" | "c33" | "c34" | "c35" | "c36" | "c37" | "c38" | "c39" | "c40" | "c41" | "c42" | "c43" | "c44" | "c45" | "c46" | "c47" | "c48" | "c49";
>C : C

type TooBig = `${A}.${B}.${C}`;
>TooBig : any

declare function f<T extends string>(x: T): T;
>f : <T extends string>(x: T) => T
>x : T

f<TooBig>("a0.b0.c0");
>f<TooBig>("a0.b0.c0") : any
>f : <T extends string>(x: T) => T
>"a0.b0.c0" : "a0.b0.c0"

type Nested = `${TooBig}.${A}`;
>Nested : `${any}.a0` | `${any}.a1` | `${any}.a10` | `${any}.a11` | `${any}.a12` | `${any}.a13` | `${any}.a14` | `${any}.a15` | `${any}.a16` | `${any}.a17` | `${any}.a18` | `${any}.a19` | `${any}.a2` | `${any}.a20` | `${any}.a21` | `${any}.a22` | `${any}.a23` | `${any}.a24` | `${any}.a25` | `${any}.a26` | `${any}.a27` | `${any}.a28` | `${any}.a29` | `${any}.a3` | `${any}.a30` | `${any}.a31` | `${any}.a32` | `${any}.a33` | `${any}.a34` | `${any}.a35` | `${any}.a36` | `${any}.a37` | `${any}.a38` | `${any}.a39` | `${any}.a4` | `${any}.a40` | `${any}.a41` | `${any}.a42` | `${any}.a43` | `${any}.a44` | `${any}.a45` | `${any}.a46` | `${any}.a47` | `${any}.a48` | `${any}.a49` | `${any}.a5` | `${any}.a6` | `${any}.a7` | `${any}.a8` | `${any}.a9`

declare const n: Nested;
>n : `${any}.a0` | `${any}.a1` | `${any}.a10` | `${any}.a11` | `${any}.a12` | `${any}.a13` | `${any}.a14` | `${any}.a15` | `${any}.a16` | `${any}.a17` | `${any}.a18` | `${any}.a19` | `${any}.a2` | `${any}.a20` | `${any}.a21` | `${any}.a22` | `${any}.a23` | `${any}.a24` | `${any}.a25` | `${any}.a26` | `${any}.a27` | `${any}.a28` | `${any}.a29` | `${any}.a3` | `${any}.a30` | `${any}.a31` | `${any}.a32` | `${any}.a33` | `${any}.a34` | `${any}.a35` | `${any}.a36` | `${any}.a37` | `${any}.a38` | `${any}.a39` | `${any}.a4` | `${any}.a40` | `${any}.a41` | `${any}.a42` | `${any}.a43` | `${any}.a44` | `${any}.a45` | `${any}.a46` | `${any}.a47` | `${any}.a48` | `${any}.a49` | `${any}.a5` | `${any}.a6` | `${any}.a7` | `${any}.a8` | `${any}.a9`

export const len = n.length;
>len : number
>n.length : number
>n : `${any}.a0` | `${any}.a1` | `${any}.a10` | `${any}.a11` | `${any}.a12` | `${any}.a13` | `${any}.a14` | `${any}.a15` | `${any}.a16` | `${any}.a17` | `${any}.a18` | `${any}.a19` | `${any}.a2` | `${any}.a20` | `${any}.a21` | `${any}.a22` | `${any}.a23` | `${any}.a24` | `${any}.a25` | `${any}.a26` | `${any}.a27` | `${any}.a28` | `${any}.a29` | `${any}.a3` | `${any}.a30` | `${any}.a31` | `${any}.a32` | `${any}.a33` | `${any}.a34` | `${any}.a35` | `${any}.a36` | `${any}.a37` | `${any}.a38` | `${any}.a39` | `${any}.a4` | `${any}.a40` | `${any}.a41` | `${any}.a42` | `${any}.a43` | `${any}.a44` | `${any}.a45` | `${any}.a46` | `${any}.a47` | `${any}.a48` | `${any}.a49` | `${any}.a5` | `${any}.a6` | `${any}.a7` | `${any}.a8` | `${any}.a9`
>length : number

// A limit error for one alias must not leak into unrelated aliases resolved in the same context.
type Force = Combined;
>Force : any

type Combined = TooBig2 | Small;
>Combined : any

type TooBig2 = `${A}.${B}.${C}`;
>TooBig2 : any

type Small = `${"x" | "y"}`;
>Small : "x" | "y"

declare const force: Force;
>force : any

let small: Small = 123;
>small : "x" | "y"
>123 : 123

21 changes: 21 additions & 0 deletions tsc/testdata/tests/cases/compiler/templateLiteralComplexityLimit.ts
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// @strict: true
// @noEmit: true

// Once the cross product limit is reported, later expansions for the same node must bail out quickly.
type A = "a0" | "a1" | "a2" | "a3" | "a4" | "a5" | "a6" | "a7" | "a8" | "a9" | "a10" | "a11" | "a12" | "a13" | "a14" | "a15" | "a16" | "a17" | "a18" | "a19" | "a20" | "a21" | "a22" | "a23" | "a24" | "a25" | "a26" | "a27" | "a28" | "a29" | "a30" | "a31" | "a32" | "a33" | "a34" | "a35" | "a36" | "a37" | "a38" | "a39" | "a40" | "a41" | "a42" | "a43" | "a44" | "a45" | "a46" | "a47" | "a48" | "a49";
type B = "b0" | "b1" | "b2" | "b3" | "b4" | "b5" | "b6" | "b7" | "b8" | "b9" | "b10" | "b11" | "b12" | "b13" | "b14" | "b15" | "b16" | "b17" | "b18" | "b19" | "b20" | "b21" | "b22" | "b23" | "b24" | "b25" | "b26" | "b27" | "b28" | "b29" | "b30" | "b31" | "b32" | "b33" | "b34" | "b35" | "b36" | "b37" | "b38" | "b39" | "b40" | "b41" | "b42" | "b43" | "b44" | "b45" | "b46" | "b47" | "b48" | "b49";
type C = "c0" | "c1" | "c2" | "c3" | "c4" | "c5" | "c6" | "c7" | "c8" | "c9" | "c10" | "c11" | "c12" | "c13" | "c14" | "c15" | "c16" | "c17" | "c18" | "c19" | "c20" | "c21" | "c22" | "c23" | "c24" | "c25" | "c26" | "c27" | "c28" | "c29" | "c30" | "c31" | "c32" | "c33" | "c34" | "c35" | "c36" | "c37" | "c38" | "c39" | "c40" | "c41" | "c42" | "c43" | "c44" | "c45" | "c46" | "c47" | "c48" | "c49";
type TooBig = `${A}.${B}.${C}`;
declare function f<T extends string>(x: T): T;
f<TooBig>("a0.b0.c0");
type Nested = `${TooBig}.${A}`;
Comment on lines +8 to +11
declare const n: Nested;
export const len = n.length;

// A limit error for one alias must not leak into unrelated aliases resolved in the same context.
type Force = Combined;
type Combined = TooBig2 | Small;
type TooBig2 = `${A}.${B}.${C}`;
type Small = `${"x" | "y"}`;
declare const force: Force;
let small: Small = 123;