From 1631f34cb2024e2727babb0f5e27ea36c80b89f3 Mon Sep 17 00:00:00 2001
From: Hongbo Zhang <bobzhang1988@gmail.com>
Date: Wed, 13 May 2026 17:11:22 +0800
Subject: [PATCH 1/2] feat(quickcheck): add Arbitrary impl for Map to match
 HashMap

Map (LinkedHashMap) was missing the @quickcheck.Arbitrary impl that HashMap
already has. Added to quickcheck/arbitrary.mbt alongside other builtin type
impls. Generates keys/values independently to avoid a circular dependency
with the tuple package.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 quickcheck/arbitrary.mbt      | 23 +++++++++++++++++++++++
 quickcheck/pkg.generated.mbti |  1 +
 2 files changed, 24 insertions(+)

diff --git a/quickcheck/arbitrary.mbt b/quickcheck/arbitrary.mbt
index c016c6d3b7..26d06c59ad 100644
--- a/quickcheck/arbitrary.mbt
+++ b/quickcheck/arbitrary.mbt
@@ -168,3 +168,26 @@ pub impl[X : Arbitrary] Arbitrary for Array[X] with arbitrary(size, rs) {
   let len = if size == 0 { 0 } else { rs.next_positive_int() % size }
   Array::makei(len, x => X::arbitrary(x, rs))
 }
+
+///|
+/// Returns a randomly generated map containing arbitrary key-value pairs.
+///
+/// Example:
+///
+/// ```mbt check
+/// test {
+///   let samples : Array[Map[Int, String]] = @quickcheck.samples(5)
+///   inspect(samples.length(), content="5")
+/// }
+/// ```
+pub impl[K : Arbitrary + Hash + Eq, V : Arbitrary] Arbitrary for Map[K, V] with arbitrary(
+  size,
+  rs,
+) {
+  let m : Map[K, V] = {}
+  let len = if size == 0 { 0 } else { rs.next_positive_int() % size }
+  for _ in 0..<len {
+    m.set(K::arbitrary(size, rs), V::arbitrary(size, rs))
+  }
+  m
+}
diff --git a/quickcheck/pkg.generated.mbti b/quickcheck/pkg.generated.mbti
index fcc80537f9..65a1b3ee03 100644
--- a/quickcheck/pkg.generated.mbti
+++ b/quickcheck/pkg.generated.mbti
@@ -38,4 +38,5 @@ pub impl Arbitrary for Bytes
 pub impl[X : Arbitrary] Arbitrary for Array[X]
 pub impl[A : Arbitrary] Arbitrary for ArrayView[A]
 pub impl[X : Arbitrary] Arbitrary for Iter[X]
+pub impl[K : Arbitrary + Hash + Eq, V : Arbitrary] Arbitrary for Map[K, V]
 

From 2a5f679e0f9ced670eae0549e35c2fb555ff8db3 Mon Sep 17 00:00:00 2001
From: Hongbo Zhang <bobzhang1988@gmail.com>
Date: Wed, 13 May 2026 17:32:36 +0800
Subject: [PATCH 2/2] fix(quickcheck): shrink size param when generating Map
 entries

Per codex review: pass loop index i as the size argument to K::arbitrary
and V::arbitrary, matching the pattern used by Array::makei. This prevents
infinite recursion when Map appears inside a recursive Arbitrary type.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 quickcheck/arbitrary.mbt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/quickcheck/arbitrary.mbt b/quickcheck/arbitrary.mbt
index 26d06c59ad..a12488e0c0 100644
--- a/quickcheck/arbitrary.mbt
+++ b/quickcheck/arbitrary.mbt
@@ -186,8 +186,8 @@ pub impl[K : Arbitrary + Hash + Eq, V : Arbitrary] Arbitrary for Map[K, V] with
 ) {
   let m : Map[K, V] = {}
   let len = if size == 0 { 0 } else { rs.next_positive_int() % size }
-  for _ in 0..<len {
-    m.set(K::arbitrary(size, rs), V::arbitrary(size, rs))
+  for i in 0..<len {
+    m.set(K::arbitrary(i, rs), V::arbitrary(i, rs))
   }
   m
 }