Sort anchors

Name trees, used to store PDF destinations (HTML anchors) have to be sorted
according to section 7.9.6 of the PDF 1.7 specification.

Fix #1352.

tests/test_pdf.py

@@ -334,6 +334,18 @@ def test_links():
     assert rects.pop(0) == [0, TOP, RIGHT, TOP - 30]
 
 
+@assert_no_logs
+def test_sorted_links():
+    # Regression test for https://github.com/Kozea/WeasyPrint/issues/1352
+    pdf = FakeHTML(string='''
+      <p id="zzz">zzz</p>
+      <p id="aaa">aaa</p>
+      <a href="#zzz">z</a>
+      <a href="#aaa">a</a>
+    ''', base_url=resource_filename('<inline HTML>')).write_pdf()
+    assert b'(zzz) [' in pdf.split(b'(aaa) [')[-1]
+
+
 @assert_no_logs
 def test_relative_links_no_height():
     # 100% wide (block), 0pt high

weasyprint/document.py

@@ -469,7 +469,8 @@ def add_hyperlinks(links, anchors, matrix, pdf, page, names):
                 page['Annots'] = pydyf.Array()
             page['Annots'].append(annot.reference)
 
-    for anchor in anchors:
+    # Anchors are name trees that have to be sorted
+    for anchor in sorted(anchors):
         anchor_name, x, y = anchor
         x, y = matrix.transform_point(x, y)
         names.append(pydyf.String(anchor_name))