TST: Ignore Producer key mismatches in PGF metadata.

Some LaTeX engines ignore the setting of this key in hyperref, but
otherwise obey the request metadata. This is likely still okay, but
leave a note in the docs as well.

Author: QuLogic

lib/matplotlib/backends/backend_pgf.py

@@ -948,6 +948,9 @@ def __init__(self, filename, *, keep_empty=True, metadata=None):
             'Creator', 'Producer', 'CreationDate', 'ModDate', and
             'Trapped'. Values have been predefined for 'Creator', 'Producer'
             and 'CreationDate'. They can be removed by setting them to `None`.
+
+            Note that some versions of LaTeX engines may ignore the 'Producer'
+            key and set it to themselves.
         """
         self._output_name = filename
         self._n_figures = 0

lib/matplotlib/tests/test_backend_pgf.py

@@ -257,13 +257,17 @@ def test_pdf_pages_metadata_check(monkeypatch, system):
     if '/PTEX.Fullbanner' in info:
         del info['/PTEX.Fullbanner']
 
+    # Some LaTeX engines ignore this setting, and state themselves as producer.
+    producer = info.pop('/Producer')
+    assert producer == f'Matplotlib pgf backend v{mpl.__version__}' or (
+            system == 'lualatex' and 'LuaTeX' in producer)
+
     assert info == {
         '/Author': 'me',
         '/CreationDate': 'D:19700101000000Z',
         '/Creator': f'Matplotlib v{mpl.__version__}, https://matplotlib.org',
         '/Keywords': 'test,pdf,multipage',
         '/ModDate': 'D:19680801000000Z',
-        '/Producer': f'Matplotlib pgf backend v{mpl.__version__}',
         '/Subject': 'Test page',
         '/Title': 'Multipage PDF with pgf',
         '/Trapped': '/True',