Add tests for negative number hsl handling, normalise degrees to range 0-1

src/textual/color.py

@@ -288,7 +288,7 @@ class Color(NamedTuple):
         if color_match is None:
             error_message = f"failed to parse {color_text!r} as a color"
             suggested_color = None
-            if not color_text.startswith(('#', 'rgb', 'hsl')):
+            if not color_text.startswith(("#", "rgb", "hsl")):
                 # Seems like we tried to use a color name: let's try to find one that is close enough:
                 suggested_color = get_suggestion(color_text, COLOR_NAME_TO_RGB.keys())
                 if suggested_color:
@@ -337,13 +337,13 @@ class Color(NamedTuple):
             )
         elif hsl is not None:
             h, s, l = hsl.split(",")
-            h = float(h) % 360
+            h = float(h) % 360 / 360
             s = percentage_string_to_float(s)
             l = percentage_string_to_float(l)
             color = Color.from_hls(h, l, s)
         elif hsla is not None:
             h, s, l, a = hsla.split(",")
-            h = clamp(float(h), 0, 360) / 360
+            h = float(h) % 360 / 360
             s = percentage_string_to_float(s)
             l = percentage_string_to_float(l)
             a = clamp(float(a), 0.0, 1.0)

src/textual/css/scalar.py

@@ -328,6 +328,11 @@ NULL_SCALAR = ScalarOffset(Scalar.from_number(0), Scalar.from_number(0))
 
 
 def percentage_string_to_float(string: str) -> float:
+    """Convert a string percentage e.g. '20%' to a float e.g. 20.0.
+
+    Args:
+        string (str): The percentage string to convert.
+    """
     string = string.strip()
     if string.endswith("%"):
         percentage = string[:-1]

tests/test_color.py

@@ -1,5 +1,4 @@
 import pytest
-
 from rich.color import Color as RichColor
 from rich.text import Text
 
@@ -136,6 +135,15 @@ def test_color_parse_clamp(input, output):
     assert Color.parse(input) == output
 
 
+def test_color_parse_hsl_negative_degrees():
+    assert Color.parse("hsl(-90, 50%, 50%)") == Color.parse("hsl(270, 50%, 50%)")
+
+
+def test_color_parse_hsla_negative_degrees():
+    assert Color.parse("hsla(-45, 50%, 50%, 0.2)") == Color.parse(
+        "hsla(315, 50%, 50%, 0.2)")
+
+
 def test_color_parse_color():
     # as a convenience, if Color.parse is passed a color object, it will return it
     color = Color(20, 30, 40, 0.5)