Added support for Select fields as combo boxes

I've decoded two PDFs, one with the combo box and another blank and extracted the binary info necessary to render it and applied to the `anchors.add_inputs` function.

docs/api_reference.rst

@@ -765,7 +765,7 @@ The ``resize``, ``cursor``, ``caret-*`` and ``nav-*`` properties are **not**
 supported.
 
 The ``appearance`` property is supported. When set to ``auto``, it displays
-form fields as PDF form fields (supported for text inputs, check boxes and
-text areas only).
+form fields as PDF form fields (supported for text inputs, check boxes, text
+areas, and select only).
 
 The ``accent-color`` property is **not** supported.

tests/test_api.py

@@ -482,15 +482,23 @@ def test_partial_pdf_custom_metadata():
     assert b'value' in stdout
 
 
-@pytest.mark.parametrize('html, field', (
-    (b'<input>', b'/Tx'),
-    (b'<input type="checkbox">', b'/Btn'),
-    (b'<textarea></textarea>', b'/Tx'),
+@pytest.mark.parametrize('html, fields', (
+    (b'<input>', [b'/Tx']),
+    (b'<input type="checkbox">', [b'/Btn']),
+    (b'<textarea></textarea>', [b'/Tx']),
+    (b'<select><option value="a">A</option></select>', [b'/Ch', b'/Opt']),
+    # The selected values will be (b) and (c) in the PDF.
+    (b'<select multiple>'
+     b'<option value="a">A</option>'
+     b'<option value="b" selected>B</option>'
+     b'<option value="c" selected>C</option>'
+     b'</select>'
+     , [b'/Ch', b'/Opt', b'[(b) (c)]']),
 ))
-def test_pdf_inputs(html, field):
+def test_pdf_inputs(html, fields):
     stdout = _run('--pdf-forms --uncompressed-pdf - -', html)
     assert b'AcroForm' in stdout
-    assert field in stdout
+    assert all(field in stdout for field in fields)
     stdout = _run('--uncompressed-pdf - -', html)
     assert b'AcroForm' not in stdout
 

weasyprint/layout/block.py

@@ -833,6 +833,18 @@ def block_container_layout(context, box, bottom_space, skip_stack,
     if next_page['page'] is None:
         next_page['page'] = new_box.page_values()[1]
 
+    if (
+        box.element and
+        box.element.tag == 'select' and
+        box.element.attrib.get('multiple') is not None and
+        not box.element.attrib.get('height') and
+        not box.element.attrib.get('max-height')
+    ):
+        # Overriding the height when the select has the multiple attribute
+        # and no height attribute
+        options_number = len([child for child in box.element])
+        new_box.height = min(box.height * 4, box.height * options_number)
+
     return (
         new_box, resume_at, next_page, adjoining_margins, collapsing_through,
         max_lines)

weasyprint/pdf/anchors.py

@@ -160,6 +160,75 @@ def add_inputs(inputs, matrix, pdf, page, resources, stream, font_map,
                 'AS': '/Yes' if checked else '/Off',
                 'DA': pydyf.String(b' '.join(field_stream.stream)),
             })
+        elif element.tag == "select":
+            # Text, password, textarea, files, and unknown
+            font_description = get_font_description(style)
+            font = pango.pango_font_map_load_font(
+                font_map, context, font_description)
+            font = stream.add_font(font)
+            font.used_in_forms = True
+
+            field_stream.set_font_size(font.hash, font_size)
+            multiple = element.attrib.get("multiple") is not None
+            options = []
+            selected_values = []
+            for option in element:
+                options.append(
+                    pydyf.Array(
+                        [f'({option.attrib.get("value")})', f'({option.text})']
+                    )
+                )
+                if option.attrib.get("selected") is not None:
+                    selected_values.append(
+                        pydyf.String(option.attrib.get("value"))
+                    )
+
+            if multiple:
+                field = pydyf.Dictionary({
+                    'DA': pydyf.String(b' '.join(field_stream.stream)),
+                    'F': 2 ** (3 - 1),  # Print flag
+                    'FT': '/Ch',
+                    'Ff': 2097152,
+                    'I': pydyf.Array([3]),
+                    'M': "(D:20231104123906+00'00')",
+                    'MK': pydyf.Dictionary({
+                        'BC': pydyf.Array([
+                            0.627451, 0.627451, 0.643137
+                        ]),
+                        'R': 0,
+                    }),
+                    'Opt': pydyf.Array(options),
+                    'P': page.reference,
+                    'Rect': pydyf.Array(rectangle),
+                    'Subtype': '/Widget',
+                    'T': pydyf.String(input_name),
+                    'Type': '/Annot',
+                    'V': pydyf.Array(selected_values)
+                    if len(selected_values) > 1
+                    else pydyf.String(element.attrib.get('value', '')),
+                })
+            else:
+                field = pydyf.Dictionary({
+                    'DA': pydyf.String(b' '.join(field_stream.stream)),
+                    'F': 2 ** (3 - 1),  # Print flag
+                    'FT': '/Ch',
+                    'Ff': 131072,
+                    'I': pydyf.Array([0]),
+                    'M': "(D:20231103110832+00'00')",
+                    'MK': pydyf.Dictionary({
+                        'BC': pydyf.Array([
+                            0.627451, 0.627451, 0.643137
+                        ]),
+                        'R': 0,
+                    }),
+                    'Opt': pydyf.Array(options),
+                    'P': page.reference,
+                    'Rect': pydyf.Array(rectangle),
+                    'Subtype': '/Widget',
+                    'T': pydyf.String(input_name),
+                    'Type': '/Annot',
+                    'V': pydyf.String(element.attrib.get('value', '')),
+                })
         else:
             # Text, password, textarea, files, and unknown
             font_description = get_font_description(style)