fix: #3153 Deque::retain / Deque::retain_map do not clear when full and wrapped

Author: Lampese

deque/deque.mbt

@@ -1346,17 +1346,18 @@ pub fn[A] Deque::retain_map(self : Deque[A], f : (A) -> A?) -> Unit {
   guard !self.is_empty() else { return }
   let { head, buf, .. } = self
   let cap = buf.length()
-  let head_len = cap - head
   let mut idx = head
+  let mut kept_len = 0
   let (front, back) = self.as_views()
   for cur in front {
     if f(cur) is Some(v) {
       buf[idx] = v
       idx += 1
+      kept_len += 1
     }
   }
   if back.length() == 0 {
-    self.truncate(idx - head)
+    self.truncate(kept_len)
     return
   }
   for cur in back {
@@ -1366,13 +1367,10 @@ pub fn[A] Deque::retain_map(self : Deque[A], f : (A) -> A?) -> Unit {
     if f(cur) is Some(v) {
       buf[idx] = v
       idx += 1
+      kept_len += 1
     }
   }
-  if idx <= self.len - head_len {
-    self.truncate(idx + head_len)
-  } else {
-    self.truncate(idx - head)
-  }
+  self.truncate(kept_len)
 }
 
 ///|
@@ -1405,17 +1403,18 @@ pub fn[A] Deque::retain(self : Deque[A], f : (A) -> Bool) -> Unit {
   guard !self.is_empty() else { return }
   let { head, buf, .. } = self
   let cap = buf.length()
-  let head_len = cap - head
   let mut idx = head
+  let mut kept_len = 0
   let (front, back) = self.as_views()
   for cur in front {
     if f(cur) {
       buf[idx] = cur
       idx += 1
+      kept_len += 1
     }
   }
   if back.length() == 0 {
-    self.truncate(idx - head)
+    self.truncate(kept_len)
     return
   }
   for cur in back {
@@ -1425,13 +1424,10 @@ pub fn[A] Deque::retain(self : Deque[A], f : (A) -> Bool) -> Unit {
     if f(cur) {
       buf[idx] = cur
       idx += 1
+      kept_len += 1
     }
   }
-  if idx <= self.len - head_len {
-    self.truncate(idx + head_len)
-  } else {
-    self.truncate(idx - head)
-  }
+  self.truncate(kept_len)
 }
 
 ///|

deque/deque_test.mbt

@@ -934,6 +934,18 @@ test "deque retain" {
   ])
 }
 
+///|
+test "deque retain clears full wrapped deque" {
+  let dq = @deque.new(capacity=4)
+  dq..push_back(1)..push_back(2)..push_back(3)..push_back(4)
+  ignore(dq.pop_front())
+  dq.push_back(5)
+  inspect(dq.as_views(), content="([2, 3, 4], [5])")
+  dq.retain(_ => false)
+  inspect(dq.as_views(), content="([], [])")
+  assert_true(dq.is_empty())
+}
+
 ///|
 test "deque retain_map" {
   let inc_if = pred => x => if pred(x) { Some(x + 1) } else { None }
@@ -983,6 +995,18 @@ test "deque retain_map" {
   ])
 }
 
+///|
+test "deque retain_map clears full wrapped deque" {
+  let dq = @deque.new(capacity=4)
+  dq..push_back(1)..push_back(2)..push_back(3)..push_back(4)
+  ignore(dq.pop_front())
+  dq.push_back(5)
+  inspect(dq.as_views(), content="([2, 3, 4], [5])")
+  dq.retain_map(_ => None)
+  inspect(dq.as_views(), content="([], [])")
+  assert_true(dq.is_empty())
+}
+
 ///|
 test "@deque.to_array/empty" {
   let dq : @deque.Deque[Int] = @deque.new()