Lazily construct collection shrink candidates

quickcheck/README.mbt.md

@@ -289,7 +289,7 @@ test "custom type shrinking" {
   debug_inspect(
     @quickcheck.Shrink::shrink(point).collect(),
     content=(
-      #|[{ x: 1, y: 1 }, { x: 0, y: 1 }, { x: 2, y: 0 }]
+      #|[{ x: 0, y: 1 }, { x: 1, y: 1 }, { x: 2, y: 0 }]
     ),
   )
 }

quickcheck/driver_test.mbt

@@ -534,3 +534,37 @@ test "context is attached to raised failures too" {
     ),
   )
 }
+
+///|
+priv struct LargeShrinkInput(Int) derive(Debug)
+
+///|
+impl @quickcheck.Arbitrary for LargeShrinkInput with fn arbitrary(_, _) {
+  LargeShrinkInput(10000)
+}
+
+///|
+impl @shrink.Shrink for LargeShrinkInput with fn shrink(input) {
+  @shrink.Shrink::shrink(input.0).map(value => LargeShrinkInput(value))
+}
+
+///|
+test "numeric shrinking reaches the boundary within the default budget" {
+  let report = @quickcheck.report(
+    (input : LargeShrinkInput) => input.0 < 5000,
+    count=1,
+    max_size=0,
+  )
+  debug_inspect(
+    report,
+    content=(
+      #|Falsified(
+      #|  counterexample=LargeShrinkInput(5000),
+      #|  tests=1,
+      #|  size=0,
+      #|  shrinks=1,
+      #|  shrink_attempts=15,
+      #|)
+    ),
+  )
+}

quickcheck/moon.pkg

@@ -27,6 +27,7 @@ import {
 }
 
 import {
+  "moonbitlang/core/bench",
   "moonbitlang/core/float",
   "moonbitlang/core/double",
 } for "test"

quickcheck/shrink/collection.mbt

@@ -14,7 +14,7 @@
 
 ///|
 pub impl[T : Shrink] Shrink for @list.List[T] with fn shrink(xs) {
-  let n = xs.length()
+  guard !xs.is_empty() else { return [||] }
   fn shr_sub_terms(lst : @list.List[T]) {
     match lst {
       Empty => [||]
@@ -25,12 +25,17 @@ pub impl[T : Shrink] Shrink for @list.List[T] with fn shrink(xs) {
     }
   }
 
-  [
-    for k = n / 2; k > 0; k = k / 2 => k
-  ]
-  .rev_iter()
-  .flat_map(k => removes_list(k, n, xs))
-  .concat(shr_sub_terms(xs))
+  [|xs.take(0)|].concat(
+    [|()|].flat_map(_ => {
+      let n = xs.length()
+      [
+        for k = n / 2; k > 0; k = k / 2 => k
+      ]
+      .iter()
+      .flat_map(k => removes_list(k, n, xs))
+      .concat([|()|].flat_map(_ => shr_sub_terms(xs)))
+    }),
+  )
 }
 
 ///|

quickcheck/shrink/collection_test.mbt

@@ -42,33 +42,43 @@ test "shrink int list" {
     @shrink.Shrink::shrink(il).collect(),
     content=(
       #|[
+      #|  <List: []>,
+      #|  <List: [1, 2, 3]>,
+      #|  <List: [4, 5, 6]>,
       #|  <List: [1, 2, 3, 4, 5]>,
       #|  <List: [1, 2, 3, 4, 6]>,
       #|  <List: [1, 2, 3, 5, 6]>,
       #|  <List: [1, 2, 4, 5, 6]>,
       #|  <List: [1, 3, 4, 5, 6]>,
       #|  <List: [2, 3, 4, 5, 6]>,
-      #|  <List: [1, 2, 3]>,
-      #|  <List: [4, 5, 6]>,
       #|  <List: [0, 2, 3, 4, 5, 6]>,
-      #|  <List: [1, 1, 3, 4, 5, 6]>,
       #|  <List: [1, 0, 3, 4, 5, 6]>,
-      #|  <List: [1, 2, 2, 4, 5, 6]>,
+      #|  <List: [1, 1, 3, 4, 5, 6]>,
       #|  <List: [1, 2, 0, 4, 5, 6]>,
-      #|  <List: [1, 2, 3, 3, 5, 6]>,
-      #|  <List: [1, 2, 3, 2, 5, 6]>,
+      #|  <List: [1, 2, 2, 4, 5, 6]>,
       #|  <List: [1, 2, 3, 0, 5, 6]>,
-      #|  <List: [1, 2, 3, 4, 4, 6]>,
-      #|  <List: [1, 2, 3, 4, 3, 6]>,
+      #|  <List: [1, 2, 3, 2, 5, 6]>,
+      #|  <List: [1, 2, 3, 3, 5, 6]>,
       #|  <List: [1, 2, 3, 4, 0, 6]>,
-      #|  <List: [1, 2, 3, 4, 5, 5]>,
-      #|  <List: [1, 2, 3, 4, 5, 3]>,
+      #|  <List: [1, 2, 3, 4, 3, 6]>,
+      #|  <List: [1, 2, 3, 4, 4, 6]>,
       #|  <List: [1, 2, 3, 4, 5, 0]>,
+      #|  <List: [1, 2, 3, 4, 5, 3]>,
+      #|  <List: [1, 2, 3, 4, 5, 5]>,
       #|]
     ),
   )
 }
 
+///|
+test "single-element list can shrink to empty" {
+  let input : @list.List[Int] = List([1])
+  debug_inspect(
+    @shrink.Shrink::shrink(input).collect(),
+    content="[<List: []>, <List: [0]>]",
+  )
+}
+
 ///|
 test "shrink queue" {
   let input = @queue.Queue([true, false, true])
@@ -97,11 +107,11 @@ test "shrink immutable vector" {
       #|  <Vector: []>,
       #|  <Vector: [4]>,
       #|  <Vector: [2]>,
-      #|  <Vector: [1, 4]>,
       #|  <Vector: [0, 4]>,
-      #|  <Vector: [2, 3]>,
-      #|  <Vector: [2, 2]>,
+      #|  <Vector: [1, 4]>,
       #|  <Vector: [2, 0]>,
+      #|  <Vector: [2, 2]>,
+      #|  <Vector: [2, 3]>,
       #|]
     ),
   )
@@ -118,13 +128,13 @@ test "shrink mutable hash set" {
       #|  <HashSet: []>,
       #|  <HashSet: [4]>,
       #|  <HashSet: [10]>,
-      #|  <HashSet: [9, 4]>,
-      #|  <HashSet: [8, 4]>,
-      #|  <HashSet: [4, 5]>,
       #|  <HashSet: [0, 4]>,
-      #|  <HashSet: [10, 3]>,
-      #|  <HashSet: [10, 2]>,
+      #|  <HashSet: [4, 5]>,
+      #|  <HashSet: [8, 4]>,
+      #|  <HashSet: [9, 4]>,
       #|  <HashSet: [0, 10]>,
+      #|  <HashSet: [10, 2]>,
+      #|  <HashSet: [10, 3]>,
       #|]
     ),
   )
@@ -140,11 +150,11 @@ test "shrink mutable sorted set" {
       #|  <SortedSet: []>,
       #|  <SortedSet: [4]>,
       #|  <SortedSet: [2]>,
-      #|  <SortedSet: [1, 4]>,
       #|  <SortedSet: [0, 4]>,
-      #|  <SortedSet: [2, 3]>,
-      #|  <SortedSet: [2]>,
+      #|  <SortedSet: [1, 4]>,
       #|  <SortedSet: [0, 2]>,
+      #|  <SortedSet: [2]>,
+      #|  <SortedSet: [2, 3]>,
       #|]
     ),
   )
@@ -161,11 +171,11 @@ test "shrink immutable hash set" {
       #|  <HashSet: []>,
       #|  <HashSet: [7]>,
       #|  <HashSet: [3]>,
-      #|  <HashSet: [2, 7]>,
       #|  <HashSet: [0, 7]>,
-      #|  <HashSet: [3, 6]>,
-      #|  <HashSet: [3, 4]>,
+      #|  <HashSet: [2, 7]>,
       #|  <HashSet: [0, 3]>,
+      #|  <HashSet: [3, 4]>,
+      #|  <HashSet: [3, 6]>,
       #|]
     ),
   )
@@ -181,11 +191,11 @@ test "shrink immutable sorted set" {
       #|  <SortedSet: []>,
       #|  <SortedSet: [5]>,
       #|  <SortedSet: [2]>,
-      #|  <SortedSet: [1, 5]>,
       #|  <SortedSet: [0, 5]>,
-      #|  <SortedSet: [2, 4]>,
-      #|  <SortedSet: [2, 3]>,
+      #|  <SortedSet: [1, 5]>,
       #|  <SortedSet: [0, 2]>,
+      #|  <SortedSet: [2, 3]>,
+      #|  <SortedSet: [2, 4]>,
       #|]
     ),
   )
@@ -205,8 +215,8 @@ test "shrink builtin map" {
       #|  [],
       #|  [(1, false)],
       #|  [(2, true)],
-      #|  [(1, false)],
       #|  [(0, true), (1, false)],
+      #|  [(1, false)],
       #|  [(2, false), (1, false)],
       #|  [(2, true), (0, false)],
       #|]
@@ -220,7 +230,12 @@ test "shrink linked set" {
   let candidates = @shrink.Shrink::shrink(input)
     .map(@set.Set::to_array)
     .collect()
-  debug_inspect(candidates, content="[[], [1], [2], [1], [0, 1], [2, 0]]")
+  debug_inspect(
+    candidates,
+    content=(
+      #|[[], [1], [2], [0, 1], [1], [2, 0]]
+    ),
+  )
 }
 
 ///|
@@ -229,7 +244,12 @@ test "shrink deque" {
   let candidates = @shrink.Shrink::shrink(input)
     .map(@deque.Deque::to_array)
     .collect()
-  debug_inspect(candidates, content="[[], [1], [2], [1, 1], [0, 1], [2, 0]]")
+  debug_inspect(
+    candidates,
+    content=(
+      #|[[], [1], [2], [0, 1], [1, 1], [2, 0]]
+    ),
+  )
 }
 
 ///|
@@ -240,7 +260,9 @@ test "shrink mutable priority queue" {
     .collect()
   debug_inspect(
     candidates,
-    content="[[], [2], [4], [3, 2], [2, 2], [2, 0], [4, 1], [4, 0]]",
+    content=(
+      #|[[], [2], [4], [2, 0], [2, 2], [3, 2], [4, 0], [4, 1]]
+    ),
   )
 }
 
@@ -252,7 +274,9 @@ test "shrink immutable priority queue" {
     .collect()
   debug_inspect(
     candidates,
-    content="[[], [2], [4], [3, 2], [2, 2], [2, 0], [4, 1], [4, 0]]",
+    content=(
+      #|[[], [2], [4], [2, 0], [2, 2], [3, 2], [4, 0], [4, 1]]
+    ),
   )
 }
 
@@ -268,8 +292,8 @@ test "shrink mutable hash map" {
       #|  <HashMap: { 2: true }>,
       #|  <HashMap: { 1: false }>,
       #|  <HashMap: { 0: false, 2: true }>,
-      #|  <HashMap: { 1: true }>,
       #|  <HashMap: { 0: true, 1: false }>,
+      #|  <HashMap: { 1: true }>,
       #|  <HashMap: { 1: false, 2: false }>,
       #|]
     ),
@@ -286,8 +310,8 @@ test "shrink mutable sorted map" {
       #|  <SortedMap: {}>,
       #|  <SortedMap: { true: 1 }>,
       #|  <SortedMap: { false: 2 }>,
-      #|  <SortedMap: { false: 1, true: 1 }>,
       #|  <SortedMap: { false: 0, true: 1 }>,
+      #|  <SortedMap: { false: 1, true: 1 }>,
       #|  <SortedMap: { false: 1 }>,
       #|  <SortedMap: { false: 2, true: 0 }>,
       #|]
@@ -306,16 +330,16 @@ test "shrink immutable hash map" {
       #|  <HashMap: {}>,
       #|  <HashMap: { 4: 2 }>,
       #|  <HashMap: { 3: 7 }>,
-      #|  <HashMap: { 2: 7, 4: 2 }>,
       #|  <HashMap: { 0: 7, 4: 2 }>,
-      #|  <HashMap: { 3: 6, 4: 2 }>,
-      #|  <HashMap: { 3: 4, 4: 2 }>,
+      #|  <HashMap: { 2: 7, 4: 2 }>,
       #|  <HashMap: { 3: 0, 4: 2 }>,
-      #|  <HashMap: { 3: 7 }>,
-      #|  <HashMap: { 2: 2, 3: 7 }>,
+      #|  <HashMap: { 3: 4, 4: 2 }>,
+      #|  <HashMap: { 3: 6, 4: 2 }>,
       #|  <HashMap: { 0: 2, 3: 7 }>,
-      #|  <HashMap: { 3: 7, 4: 1 }>,
+      #|  <HashMap: { 2: 2, 3: 7 }>,
+      #|  <HashMap: { 3: 7 }>,
       #|  <HashMap: { 3: 7, 4: 0 }>,
+      #|  <HashMap: { 3: 7, 4: 1 }>,
       #|]
     ),
   )
@@ -332,8 +356,8 @@ test "shrink immutable sorted map" {
       #|  <SortedMap: { 3: true }>,
       #|  <SortedMap: { 1: false }>,
       #|  <SortedMap: { 0: false, 3: true }>,
-      #|  <SortedMap: { 1: false, 2: true }>,
       #|  <SortedMap: { 0: true, 1: false }>,
+      #|  <SortedMap: { 1: false, 2: true }>,
       #|  <SortedMap: { 1: false, 3: false }>,
       #|]
     ),

quickcheck/shrink/composite.mbt

@@ -16,7 +16,7 @@
 pub impl[T : Shrink] Shrink for T? with fn shrink(x) {
   match x {
     None => [||]
-    Some(v) => Shrink::shrink(v).map(v1 => Some(v1)).concat([|None|])
+    Some(v) => [|None|].concat(Shrink::shrink(v).map(v1 => Some(v1)))
   }
 }
 
@@ -47,7 +47,7 @@ pub impl[X : Shrink] Shrink for Array[X] with fn shrink(xs) {
   ]
   .iter()
   .flat_map(k => removes_array(k, n, xs))
-  .concat(shr_sub_terms(view))
+  .concat([|()|].flat_map(_ => shr_sub_terms(view)))
 }
 
 ///|