pass max width to latex adjustbox

Problem:
When creating large diagrams using plantuml, they can quickly get too wide for a
pdf page.  For images in the png, pdf and svg format, this problem is handled by
the sphinx-provided "sphinxincludegraphics" latex command, which resizes the
included graphic if needed.  As tikz images are embedded using the "\input"
command, this resize logic is not applicable for them.

Solution:
I would suggest to use the "max-width" option (which is already somehow
implemented but not documented) to allow the user to specify a maximum width.
The "adjustbox" macro, which is already being used for giving an absolute size
for an image, also supports this type of maximum size.  This way, the image is
not resized if it fits, but only if it would exceed the given size.

sphinxcontrib/plantuml.py

@@ -632,7 +632,7 @@ def _lookup_latex_format(fmt):
         )
 
 
-def _latex_adjustbox_options(self, node):
+def _latex_adjustbox_options(self, node):  # noqa: C901
     adjustbox_options = []
     if 'width' in node:
         if 'scale' in node:
@@ -651,6 +651,13 @@ def _latex_adjustbox_options(self, node):
     if 'scale' in node:
         if not adjustbox_options:
             adjustbox_options.append('scale=%s' % (float(node['scale']) / 100.0))
+    if 'max-width' in node:
+        if 'scale' in node:
+            w = self.latex_image_length(node['max-width'], node['scale'])
+        else:
+            w = self.latex_image_length(node['max-width'])
+        if w:
+            adjustbox_options.append('max width=%s' % w)
     return adjustbox_options
 
 

tests/test_functional.py

@@ -309,6 +309,19 @@ def test_buildlatex_simple_height_with_tikz():
                      readfile('plantuml_fixture.tex'))
 
 
+@with_runsphinx('latex', plantuml_latex_output_format='tikz')
+def test_buildlatex_simple_max_width_with_tikz():
+    """Generate simple LaTeX with TikZ
+
+    .. uml::
+       :max-width: 50mm
+
+       Hello
+    """
+    assert re.search(br'\\adjustbox\{max width=50mm\}\{\\input\{+plantuml-',
+                     readfile('plantuml_fixture.tex'))
+
+
 @with_runsphinx('latex', plantuml_latex_output_format='pdf')
 def test_buildlatex_simple_with_pdf():
     """Generate simple LaTeX with PDF