From 62c97279b4107ea92ff723a10b19469406d22e2e Mon Sep 17 00:00:00 2001
From: Tuomas Hietanen <thorium@iki.fi>
Date: Tue, 11 Nov 2025 12:46:43 +0000
Subject: [PATCH] Add a unit-test of complex (problematic) active pattern

---
 .../PatternMatching/ActivePattern18425.fs     | 68 +++++++++++++++++++
 .../FSharp.Compiler.ComponentTests.fsproj     |  1 +
 2 files changed, 69 insertions(+)
 create mode 100644 tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/ActivePattern18425.fs

diff --git a/tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/ActivePattern18425.fs b/tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/ActivePattern18425.fs
new file mode 100644
index 00000000000..5e49f9db8bc
--- /dev/null
+++ b/tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/ActivePattern18425.fs
@@ -0,0 +1,68 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Conformance.PatternMatching
+
+open Xunit
+open FSharp.Test
+open FSharp.Test.Compiler
+
+module ActivePattern18425 =
+
+    // Test that deeply nested active patterns compile in reasonable time
+    [<Fact>]
+    let ``Deeply nested active patterns should compile efficiently`` () =
+        FSharp """
+module Test
+
+let inline (|Or'|_|) x =
+    match x with
+    | (a, b) -> Some(a, b)
+
+let inline (|And'|_|) x =
+    match x with
+    | (a, b) -> Some(a, b)
+
+let inline (|Not'|_|) x = Some x
+
+// Function with deeply nested active patterns  
+let testFunction x =
+    match x with
+    // Deep nesting of active patterns (depth > 5)
+    | Or'(And'(Not' p1, p2), And'(p3, Not' p4)) -> 1
+    | Or'(And'(p1, Not' p2), And'(Not' p3, p4)) -> 2
+    | Or'(Not'(And'(p1, p2)), And'(Not' p3, p4)) -> 3
+    | Or'(And'(Not' p1, Not' p2), And'(p3, p4)) -> 4
+    | Or'(And'(p1, p2), Or'(And'(p3, p4), And'(p5, p6))) -> 5
+    | Or'(Or'(And'(p1, p2), And'(p3, p4)), And'(p5, p6)) -> 6
+    | _ -> 7
+        """
+        |> compile
+        |> shouldSucceed
+
+
+    // Test that many active patterns in one clause compile efficiently
+    [<Fact>]
+    let ``Many active patterns in one clause should compile efficiently`` () =
+        FSharp """
+module Test
+
+let inline (|Pat1|_|) x = if fst x = 1 then Some (snd x) else None
+let inline (|Pat2|_|) x = if fst x = 2 then Some (snd x) else None
+let inline (|Pat3|_|) x = if fst x = 3 then Some (snd x) else None
+let inline (|Pat4|_|) x = if fst x = 4 then Some (snd x) else None
+let inline (|Pat5|_|) x = if fst x = 5 then Some (snd x) else None
+let inline (|Pat6|_|) x = if fst x = 6 then Some (snd x) else None
+let inline (|Pat7|_|) x = if fst x = 7 then Some (snd x) else None
+let inline (|Pat8|_|) x = if fst x = 8 then Some (snd x) else None
+let inline (|Pat9|_|) x = if fst x = 9 then Some (snd x) else None
+let inline (|Pat10|_|) x = if fst x = 10 then Some (snd x) else None
+let inline (|Pat11|_|) x = if fst x = 11 then Some (snd x) else None
+
+// More than 10 active patterns in a pattern
+let testFunction x =
+    match x with
+    | Pat1 p1 when p1 > 0 -> Pat2 p1, Pat3 p1, Pat4 p1, Pat5 p1, Pat6 p1, Pat7 p1, Pat8 p1, Pat9 p1, Pat10 p1, Pat11 p1
+    | _ -> None, None, None, None, None, None, None, None, None, None
+        """
+        |> compile
+        |> shouldSucceed
diff --git a/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj b/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
index 8f5ace7aade..29a2003e9df 100644
--- a/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
+++ b/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
@@ -112,6 +112,7 @@
     <Compile Include="Conformance\PatternMatching\DynamicTypeTest\DynamicTypeTest.fs" />
     <Compile Include="Conformance\PatternMatching\Expression\Expression.fs" />
     <Compile Include="Conformance\PatternMatching\Named\Named.fs" />
+    <Compile Include="Conformance\PatternMatching\ActivePattern18425.fs" />
     <Compile Include="Conformance\PatternMatching\Null\Null.fs" />
     <Compile Include="Conformance\PatternMatching\Record\Record.fs" />
     <Compile Include="Conformance\PatternMatching\SimpleConstant\SimpleConstant.fs" />