SVG: read a light-dark() color as its light color

CHANGELOG.md

@@ -23,6 +23,7 @@ This can also be enabled programmatically with `warnings.simplefilter('default',
 ### Fixed
 * SVG: `currentColor` and `inherit` are now read regardless of case, like the color keywords, so `fill="currentcolor"`, as in the Font Awesome icons of many web pages, no longer fails with `ValueError: unsupported color specification currentcolor` - thanks to @RavSinghChandan
 * SVG: black or gray text no longer fails with an `AssertionError` when it is in a `<tspan>` that has its own style, as in every text written by Inkscape: the check on the text color left out `DeviceGray`, the color fpdf2 uses for black and gray - thanks to @RavSinghChandan
+* SVG: a `light-dark()` color, as in the icons of the Zensical documentation theme, is now read as its first, light color, which is the one CSS uses when no `color-scheme` is set, instead of failing with `ValueError: unsupported color specification` - thanks to @RavSinghChandan
 * SVG: an image without an `xmlns` declaration no longer fails with `ValueError: substring not found` when it contains a tag that is not supported, such as `<title>` or `<script>`; the tag is skipped with a warning, as in an image that declares the namespace - thanks to @RavSinghChandan
 * `FPDF.text()` raises a clear `ValueError` for a NaN or infinite `x` or `y`, like `FPDF.set_xy()`, instead of writing `nan` or `inf` into the page, which is not a valid PDF number - thanks to @RavSinghChandan
 * SVG: `clip-path="none"`, as written by Inkscape, no longer fails with an `AssertionError`, and a `url(#id)` reference to a clip path whose id contains a `-` or a `.`, or that is quoted, now finds that clip path, instead of failing with a `KeyError` or clipping with another one whose id is the part before the `-` or `.` - thanks to @RavSinghChandan

fpdf/svg.py

@@ -266,6 +266,35 @@ def svgcolor(colorstr: str) -> DeviceRGB | DeviceGray:
     raise ValueError(f"unsupported color specification {colorstr}")
 
 
+def _light_color(colorstr: str) -> str:
+    """
+    CSS Color 5: without a color-scheme, which SVG documents rarely set,
+    light-dark() is its first, light color. Any other value is returned as is.
+    """
+    stripped = colorstr.strip()
+    if stripped.lower().startswith("light-dark(") and stripped.endswith(")"):
+        return _light_color(
+            _split_top_level_commas(stripped[len("light-dark(") : -1])[0].strip()
+        )
+    return colorstr
+
+
+def _split_top_level_commas(value: str) -> list[str]:
+    """Split on the commas that are not inside parentheses, as in "rgb(1, 2, 3), red"."""
+    parts: list[str] = []
+    depth, start = 0, 0
+    for index, character in enumerate(value):
+        if character == "(":
+            depth += 1
+        elif character == ")":
+            depth -= 1
+        elif character == "," and depth == 0:
+            parts.append(value[start:index])
+            start = index + 1
+    parts.append(value[start:])
+    return parts
+
+
 @force_nodocument
 def convert_stroke_width(incoming: str) -> Optional[float]:
     val = resolve_length(incoming)
@@ -328,6 +357,8 @@ def optional(
 @force_nodocument
 def svg_paint(colorstr: Optional[str]) -> Any:
     """A fill or stroke paint: "transparent" paints nothing, like "none"."""
+    if colorstr:
+        colorstr = _light_color(colorstr)
     if colorstr and colorstr.startswith("url("):
         return None
     if colorstr and colorstr.strip().lower() == "transparent":
@@ -1451,7 +1482,7 @@ def _parse_gradient_stops(
                 stop_color = stop_element.attrib.get("stop-color", "black")
 
             try:
-                color_obj = svgcolor(stop_color)
+                color_obj = svgcolor(_light_color(stop_color))
 
                 color_alpha = color_obj.a if color_obj.a is not None else 1.0
                 effective_opacity = color_alpha * stop_opacity

test/svg/parameters.py

@@ -573,6 +573,36 @@ def Gs(**kwargs):
         pytest.raises(ValueError),
         id="fill color invalid",
     ),
+    pytest.param(
+        '<path fill="light-dark(rgb(255, 0, 0), rgba(226, 228, 233, 0.82))"/>',
+        Gs(fill_color="#f00"),
+        no_error(),
+        id="fill color light-dark()",
+    ),
+    pytest.param(
+        '<path stroke="Light-Dark(#00f, white)"/>',
+        Gs(stroke_color="#00f"),
+        no_error(),
+        id="stroke color light-dark() uppercase",
+    ),
+    pytest.param(
+        '<path fill="light-dark(1, red)"/>',
+        Gs(),
+        pytest.raises(ValueError),
+        id="fill color light-dark() invalid",
+    ),
+    pytest.param(
+        '<path fill="light-dark(transparent, red)"/>',
+        Gs(fill_color=None),
+        no_error(),
+        id="fill color light-dark() transparent",
+    ),
+    pytest.param(
+        '<path stroke="light-dark(currentColor, white)"/>',
+        Gs(stroke_color=GraphicsStyle.INHERIT),
+        no_error(),
+        id="stroke color light-dark() currentColor",
+    ),
     pytest.param(
         '<path fill-rule="inherit"/>',
         Gs(intersection_rule=GraphicsStyle.INHERIT),