SVG: clip away an element whose clipPath is empty

CHANGELOG.md

@@ -21,6 +21,7 @@ This can also be enabled programmatically with `warnings.simplefilter('default',
 * Chinese translation of the [Tuto 7 - Creating PDF/A Documents](https://py-pdf.github.io/fpdf2/Tutorial-zh.html#-pdfa) tutorial section - _cf._ [issue #267](https://github.com/py-pdf/fpdf2/issues/267) - _cf._ [PR #2138](https://github.com/py-pdf/fpdf2/pull/2138) - thanks to @zheng-guannan577*
 * `FPDF.write_html()` makes the `id` of an element, and the `name` of an `<a>`, a named destination, so that `<a href="#...">` links within the document work, like in browsers, instead of raising `FPDFException: Named destination ... was referenced but never set` - thanks to @RavSinghChandan
 ### Fixed
+* SVG: an element whose `clip-path` references a `<clipPath>` without any shape to clip with, such as one without children or with only a `<g>`, is now clipped away, as the SVG specification says, and one whose `clip-path` references no `<clipPath>` is drawn without clipping, with a warning, as in browsers, instead of failing with `KeyError` - thanks to @RavSinghChandan
 * SVG: an `@import`, `@charset` or other at-rule without a block at the start of a `<style>`, such as the `@import` of a Google Font, no longer hides the CSS rule that follows it; a `;` inside its URL, as in `wght@600;700`, is part of the URL - thanks to @RavSinghChandan
 * `FPDF.write_html()`: a link with `href="#"`, as in the "Back to top" links of many web pages, now goes to the top of the document, like in browsers, instead of making `output()` fail with `FPDFException: Named destination '' was referenced but never set` - thanks to @RavSinghChandan
 * `FPDF.output()` no longer fails with `struct.error: unpack requires a buffer of 2 bytes` for a font with Apple bitmap tables, such as the `Geneva.ttf` and `Cochin.ttc` of macOS: their `bdat` and `bloc` tables are now dropped when subsetting, like the `EBDT` and `EBLC` tables they correspond to - thanks to @RavSinghChandan

fpdf/svg.py

@@ -3078,8 +3078,23 @@ def apply_clipping_path(
             clip_value = svg_element.attrib.get("clip-path")
         # "none" (or any value that is not a url(#id) reference) clips nothing
         clipping_path_id = self._extract_gradient_id(clip_value)
-        if clipping_path_id:
-            stylable.clipping_path = self.cross_references[clipping_path_id]
+        if not clipping_path_id:
+            return
+        element = self._elements_by_id.get(clipping_path_id)
+        if element is None or element.tag not in xmlns_lookup("svg", "clipPath"):
+            # Browsers draw the element without clipping it
+            LOGGER.warning(
+                "Ignoring clip-path reference to nonexistent <clipPath> %s",
+                clipping_path_id,
+            )
+            return
+        clipping_path = self.cross_references.get(clipping_path_id)
+        if clipping_path is None:
+            # A <clipPath> without any shape it can clip with, such as one without
+            # children or with only a <g>, is empty: it clips the whole element away
+            clipping_path = ClippingPath()
+            clipping_path.rectangle(0, 0, 0, 0)
+        stylable.clipping_path = clipping_path
 
     @force_nodocument
     def build_image(self, image: "Element") -> "SVGImage | GraphicsContext":

test/svg/test_svg.py

@@ -1153,6 +1153,41 @@ def test_svg_use_of_use_of_nothing(self, referenced, caplog):
         assert outer.path_items[0].path_items == []
         assert "#clone" not in caplog.text
 
+    @pytest.mark.parametrize(
+        "clip_path",
+        [
+            '<clipPath id="c"/>',
+            # children that cannot be part of a clipping path
+            '<clipPath id="c"><g><rect width="5" height="5"/></g></clipPath>',
+            '<clipPath id="c"><switch><rect width="5" height="5"/></switch></clipPath>',
+        ],
+    )
+    def test_svg_empty_clip_path(self, clip_path):
+        """A clipping path without any shape clips the whole element away."""
+        pdf = fpdf.FPDF()
+        pdf.compress = False
+        pdf.add_page()
+        fpdf.svg.SVGObject(
+            '<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10">'
+            f'{clip_path}<rect width="10" height="10" fill="red" clip-path="url(#c)"/>'
+            "</svg>"
+        ).draw_to_page(pdf)
+        assert "1 0 0 rg 0 0 m W n 0 0 m 0 0 10 10 re f" in bytes(pdf.output()).decode(
+            "latin-1"
+        )
+
+    @pytest.mark.parametrize("target", ["", '<rect id="c" width="5" height="5"/>'])
+    def test_svg_clip_path_reference_to_nothing(self, target, caplog):
+        """Browsers draw an element whose clip-path references no clipPath unclipped."""
+        svg = fpdf.svg.SVGObject(
+            f'<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"><defs>{target}'
+            '</defs><path d="M0 0h5v5z" fill="red" clip-path="url(#c)"/></svg>'
+        )
+        assert svg.base_group.path_items[-1].clipping_path is None
+        assert (
+            "Ignoring clip-path reference to nonexistent <clipPath> #c" in caplog.text
+        )
+
     def test_svg_display_none_referenced(self):
         """An element in a hidden group can still be drawn by a <use>."""
         svg = fpdf.svg.SVGObject(