Fix zero-capacity lists (exaloop#420)

stdlib/internal/types/collections/list.codon

@@ -9,6 +9,8 @@ class List:
         self.len = 0
 
     def __init__(self, capacity: int):
+        if capacity < 0:
+            capacity = 0
         self.arr = Array[T](capacity)
         self.len = 0
 
@@ -372,6 +374,8 @@ class List:
     def _resize_if_full(self):
         if self.len == self.arr.len:
             new_cap = (1 + 3 * self.len) // 2
+            if new_cap <= 0:
+                new_cap = 1
             self._resize(new_cap)
 
     def __hash__(self) -> int:

test/core/containers.codon

@@ -299,6 +299,24 @@ def test_list():
     assert list(reversed(list('abc'))) == ['c', 'b', 'a']
     assert list(list('abc')[::-1]) == ['c', 'b', 'a']
     assert list(reversed(List[str]())) == List[str]()
+
+    # https://github.com/exaloop/codon/issues/402
+    b1 = [1 for _ in range(0)]
+    b2 = [str(x) for x in b1]
+    b3 = List[float](capacity=0)
+    b4 = List[float](capacity=-1)
+    assert len(b1) == 0
+    assert len(b2) == 0
+    assert len(b3) == 0
+    assert len(b4) == 0
+    b1.append(42)
+    b2.append('a')
+    b3.append(4.2)
+    b4.append(2.4)
+    assert b1 == [42]
+    assert b2 == ['a']
+    assert b3 == [4.2]
+    assert b4 == [2.4]
 test_list()
 
 @test