From 77d63f529a929a8676d813619e72b1e86ce0e4b0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Burzy=C5=84ski?= <mateuszburzynski@gmail.com>
Date: Fri, 11 Sep 2026 10:12:27 +0200
Subject: [PATCH] Fixed a crash related to variadic tuple elements with
 intersections containing `InstantiableNonPrimitive`

---
 tsc/internal/checker/checker.go                     | 11 ++++++++++-
 .../compiler/recursiveConditionalCrash5.errors.txt  | 10 ++++++++++
 .../compiler/recursiveConditionalCrash5.symbols     | 13 +++++++++++++
 .../compiler/recursiveConditionalCrash5.types       |  8 ++++++++
 .../cases/compiler/recursiveConditionalCrash5.ts    |  6 ++++++
 5 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.errors.txt
 create mode 100644 tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.symbols
 create mode 100644 tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.types
 create mode 100644 tsc/testdata/tests/cases/compiler/recursiveConditionalCrash5.ts

diff --git a/tsc/internal/checker/checker.go b/tsc/internal/checker/checker.go
index ca77e97af8547..e3215baa00120 100644
--- a/tsc/internal/checker/checker.go
+++ b/tsc/internal/checker/checker.go
@@ -23707,7 +23707,9 @@ func (n *TupleNormalizer) normalize(c *Checker, elementTypes []*Type, elementInf
 		if info.flags&ElementFlagsVariadic != 0 {
 			if t.flags&TypeFlagsAny != 0 {
 				n.add(t, TupleElementInfo{flags: ElementFlagsRest, labeledDeclaration: info.labeledDeclaration})
-			} else if t.flags&TypeFlagsInstantiableNonPrimitive != 0 || c.isGenericMappedType(t) {
+			} else if someContainedType(t, func(t *Type) bool {
+				return t.flags&TypeFlagsInstantiableNonPrimitive != 0 || c.isGenericMappedType(t)
+			}) {
 				// Generic variadic elements stay as they are.
 				n.add(t, info)
 			} else if isTupleType(t) {
@@ -26893,6 +26895,13 @@ func everyType(t *Type, f func(*Type) bool) bool {
 	return f(t)
 }
 
+func someContainedType(t *Type, f func(*Type) bool) bool {
+	if t.flags&TypeFlagsUnionOrIntersection != 0 {
+		return core.Some(t.Types(), f)
+	}
+	return f(t)
+}
+
 func everyContainedType(t *Type, f func(*Type) bool) bool {
 	if t.flags&TypeFlagsUnionOrIntersection != 0 {
 		return core.Every(t.Types(), f)
diff --git a/tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.errors.txt b/tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.errors.txt
new file mode 100644
index 0000000000000..ac99cf2a6d542
--- /dev/null
+++ b/tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.errors.txt
@@ -0,0 +1,10 @@
+recursiveConditionalCrash5.ts(3,60): error TS2589: Type instantiation is excessively deep and possibly infinite.
+
+
+==== recursiveConditionalCrash5.ts (1 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/63040
+    
+    type StringTreeArrayAsTuple<T> = (T extends [...infer R] ? [...StringTreeArrayAsTuple<R>] : never) & boolean;
+                                                               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
+    
\ No newline at end of file
diff --git a/tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.symbols b/tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.symbols
new file mode 100644
index 0000000000000..088577dcd7b43
--- /dev/null
+++ b/tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.symbols
@@ -0,0 +1,13 @@
+//// [tests/cases/compiler/recursiveConditionalCrash5.ts] ////
+
+=== recursiveConditionalCrash5.ts ===
+// https://github.com/microsoft/TypeScript/issues/63040
+
+type StringTreeArrayAsTuple<T> = (T extends [...infer R] ? [...StringTreeArrayAsTuple<R>] : never) & boolean;
+>StringTreeArrayAsTuple : Symbol(StringTreeArrayAsTuple, Decl(recursiveConditionalCrash5.ts, 0, 0))
+>T : Symbol(T, Decl(recursiveConditionalCrash5.ts, 2, 28))
+>T : Symbol(T, Decl(recursiveConditionalCrash5.ts, 2, 28))
+>R : Symbol(R, Decl(recursiveConditionalCrash5.ts, 2, 53))
+>StringTreeArrayAsTuple : Symbol(StringTreeArrayAsTuple, Decl(recursiveConditionalCrash5.ts, 0, 0))
+>R : Symbol(R, Decl(recursiveConditionalCrash5.ts, 2, 53))
+
diff --git a/tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.types b/tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.types
new file mode 100644
index 0000000000000..671d71e3f6470
--- /dev/null
+++ b/tsc/testdata/baselines/reference/compiler/recursiveConditionalCrash5.types
@@ -0,0 +1,8 @@
+//// [tests/cases/compiler/recursiveConditionalCrash5.ts] ////
+
+=== recursiveConditionalCrash5.ts ===
+// https://github.com/microsoft/TypeScript/issues/63040
+
+type StringTreeArrayAsTuple<T> = (T extends [...infer R] ? [...StringTreeArrayAsTuple<R>] : never) & boolean;
+>StringTreeArrayAsTuple : StringTreeArrayAsTuple<T>
+
diff --git a/tsc/testdata/tests/cases/compiler/recursiveConditionalCrash5.ts b/tsc/testdata/tests/cases/compiler/recursiveConditionalCrash5.ts
new file mode 100644
index 0000000000000..87641a5ca9277
--- /dev/null
+++ b/tsc/testdata/tests/cases/compiler/recursiveConditionalCrash5.ts
@@ -0,0 +1,6 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/63040
+
+type StringTreeArrayAsTuple<T> = (T extends [...infer R] ? [...StringTreeArrayAsTuple<R>] : never) & boolean;