From 03c1b1843597b1d83f557e98a25ebc86778b430b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Burzy=C5=84ski?= <mateuszburzynski@gmail.com>
Date: Sun, 16 Nov 2025 16:37:37 +0100
Subject: [PATCH] Don't create substition types when extending type with infer
 type parameters

---
 src/compiler/checker.ts                       |  2 +-
 ...aintLeakThroughInferTypeParameter1.symbols | 43 +++++++++++++++++++
 ...traintLeakThroughInferTypeParameter1.types | 35 +++++++++++++++
 ...onstraintLeakThroughInferTypeParameter1.ts | 20 +++++++++
 4 files changed, 99 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.symbols
 create mode 100644 tests/baselines/reference/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.types
 create mode 100644 tests/cases/compiler/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index ba5765c0826a3..274f44725e70e 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -17200,7 +17200,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             }
             // Always substitute on type parameters, regardless of variance, since even
             // in contravariant positions, they may rely on substituted constraints to be valid
-            if ((covariant || type.flags & TypeFlags.TypeVariable) && parent.kind === SyntaxKind.ConditionalType && node === (parent as ConditionalTypeNode).trueType) {
+            if ((covariant || type.flags & TypeFlags.TypeVariable) && parent.kind === SyntaxKind.ConditionalType && node === (parent as ConditionalTypeNode).trueType && !getInferTypeParameters(parent as ConditionalTypeNode)) {
                 const constraint = getImpliedConstraint(type, (parent as ConditionalTypeNode).checkType, (parent as ConditionalTypeNode).extendsType);
                 if (constraint) {
                     constraints = append(constraints, constraint);
diff --git a/tests/baselines/reference/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.symbols b/tests/baselines/reference/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.symbols
new file mode 100644
index 0000000000000..9684524da8faf
--- /dev/null
+++ b/tests/baselines/reference/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.symbols
@@ -0,0 +1,43 @@
+//// [tests/cases/compiler/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts] ////
+
+=== distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts ===
+// https://github.com/microsoft/TypeScript/issues/62761
+
+type Value = 1 | 2
+>Value : Symbol(Value, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 0, 0))
+
+type Result = [Value] extends [infer V]
+>Result : Symbol(Result, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 2, 18))
+>Value : Symbol(Value, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 0, 0))
+>V : Symbol(V, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 4, 36))
+
+  ? V extends unknown
+>V : Symbol(V, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 4, 36))
+
+    ? [V, Value]
+>V : Symbol(V, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 4, 36))
+>Value : Symbol(Value, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 0, 0))
+
+    : never
+  : never
+
+type Value2 = { prop: 1 | 2 };
+>Value2 : Symbol(Value2, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 8, 9))
+>prop : Symbol(prop, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 10, 15))
+
+type Result2 = Value2 extends { prop: infer V }
+>Result2 : Symbol(Result2, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 10, 30))
+>Value2 : Symbol(Value2, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 8, 9))
+>prop : Symbol(prop, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 12, 31))
+>V : Symbol(V, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 12, 43))
+
+  ? V extends unknown
+>V : Symbol(V, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 12, 43))
+
+    ? [V, Value2]
+>V : Symbol(V, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 12, 43))
+>Value2 : Symbol(Value2, Decl(distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts, 8, 9))
+
+    : never
+  : never;
+
diff --git a/tests/baselines/reference/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.types b/tests/baselines/reference/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.types
new file mode 100644
index 0000000000000..191129ffecdd4
--- /dev/null
+++ b/tests/baselines/reference/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.types
@@ -0,0 +1,35 @@
+//// [tests/cases/compiler/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts] ////
+
+=== distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts ===
+// https://github.com/microsoft/TypeScript/issues/62761
+
+type Value = 1 | 2
+>Value : Value
+>      : ^^^^^
+
+type Result = [Value] extends [infer V]
+>Result : [1, Value] | [2, Value]
+>       : ^^^^^^^^^^^^^^^^^^^^^^^
+
+  ? V extends unknown
+    ? [V, Value]
+    : never
+  : never
+
+type Value2 = { prop: 1 | 2 };
+>Value2 : Value2
+>       : ^^^^^^
+>prop : 1 | 2
+>     : ^^^^^
+
+type Result2 = Value2 extends { prop: infer V }
+>Result2 : [1, Value2] | [2, Value2]
+>        : ^^^^^^^^^^^^^^^^^^^^^^^^^
+>prop : V
+>     : ^
+
+  ? V extends unknown
+    ? [V, Value2]
+    : never
+  : never;
+
diff --git a/tests/cases/compiler/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts b/tests/cases/compiler/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts
new file mode 100644
index 0000000000000..51fe44143199a
--- /dev/null
+++ b/tests/cases/compiler/distributiveConditionalTypeNoConstraintLeakThroughInferTypeParameter1.ts
@@ -0,0 +1,20 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/62761
+
+type Value = 1 | 2
+
+type Result = [Value] extends [infer V]
+  ? V extends unknown
+    ? [V, Value]
+    : never
+  : never
+
+type Value2 = { prop: 1 | 2 };
+
+type Result2 = Value2 extends { prop: infer V }
+  ? V extends unknown
+    ? [V, Value2]
+    : never
+  : never;