From 005d5946c089b8319470cbea96db94cc6bd601bc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Burzy=C5=84ski?= <mateuszburzynski@gmail.com>
Date: Wed, 11 Feb 2026 20:08:57 +0100
Subject: [PATCH] Fixed a crash related to variadic tuple elements with
 intersections containing `InstantiableNonPrimitive`

---
 src/compiler/checker.ts                             |  6 +++++-
 .../reference/recursiveConditionalCrash5.errors.txt | 10 ++++++++++
 .../reference/recursiveConditionalCrash5.symbols    | 13 +++++++++++++
 .../reference/recursiveConditionalCrash5.types      |  9 +++++++++
 tests/cases/compiler/recursiveConditionalCrash5.ts  |  6 ++++++
 5 files changed, 43 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/recursiveConditionalCrash5.errors.txt
 create mode 100644 tests/baselines/reference/recursiveConditionalCrash5.symbols
 create mode 100644 tests/baselines/reference/recursiveConditionalCrash5.types
 create mode 100644 tests/cases/compiler/recursiveConditionalCrash5.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 8fa3c4fce2a4a..fb5fdf6069354 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -17965,7 +17965,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 if (type.flags & TypeFlags.Any) {
                     addElement(type, ElementFlags.Rest, target.labeledElementDeclarations?.[i]);
                 }
-                else if (type.flags & TypeFlags.InstantiableNonPrimitive || isGenericMappedType(type)) {
+                else if (someContainedType(type, t => !!(t.flags & TypeFlags.InstantiableNonPrimitive) || isGenericMappedType(type))) {
                     // Generic variadic elements stay as they are.
                     addElement(type, ElementFlags.Variadic, target.labeledElementDeclarations?.[i]);
                 }
@@ -28515,6 +28515,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return type.flags & TypeFlags.Union ? every((type as UnionType).types, f) : f(type);
     }
 
+    function someContainedType(type: Type, f: (t: Type) => boolean): boolean {
+        return type.flags & TypeFlags.UnionOrIntersection ? some((type as UnionOrIntersectionType).types, f) : f(type);
+    }
+
     function everyContainedType(type: Type, f: (t: Type) => boolean): boolean {
         return type.flags & TypeFlags.UnionOrIntersection ? every((type as UnionOrIntersectionType).types, f) : f(type);
     }
diff --git a/tests/baselines/reference/recursiveConditionalCrash5.errors.txt b/tests/baselines/reference/recursiveConditionalCrash5.errors.txt
new file mode 100644
index 0000000000000..ac99cf2a6d542
--- /dev/null
+++ b/tests/baselines/reference/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/tests/baselines/reference/recursiveConditionalCrash5.symbols b/tests/baselines/reference/recursiveConditionalCrash5.symbols
new file mode 100644
index 0000000000000..088577dcd7b43
--- /dev/null
+++ b/tests/baselines/reference/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/tests/baselines/reference/recursiveConditionalCrash5.types b/tests/baselines/reference/recursiveConditionalCrash5.types
new file mode 100644
index 0000000000000..d920776cd72ed
--- /dev/null
+++ b/tests/baselines/reference/recursiveConditionalCrash5.types
@@ -0,0 +1,9 @@
+//// [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/tests/cases/compiler/recursiveConditionalCrash5.ts b/tests/cases/compiler/recursiveConditionalCrash5.ts
new file mode 100644
index 0000000000000..87641a5ca9277
--- /dev/null
+++ b/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;