Improve sphinx warnings

This commit intends to improve the warning emitted by the extension; to include
source mapping to the error origin, and set the type for all warning (this means
e.g. you can suppress them:
https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-suppress_warnings)

sphinxcontrib/plantuml.py

@@ -353,7 +353,9 @@ def _render_files(self, keys, fileformat):
         serr = p.communicate()[1]
         if p.returncode != 0:
             if self.builder.config.plantuml_syntax_error_image:
-                logger.warning('error while running plantuml\n\n%s' % serr)
+                logger.warning(
+                    'error while running plantuml\n\n%s' % serr, type='plantuml'
+                )
             else:
                 raise PlantUmlError('error while running plantuml\n\n%s' % serr)
 
@@ -384,7 +386,11 @@ def render(self, node, fileformat):
             serr = p.communicate(node['uml'].encode('utf-8'))[1]
             if p.returncode != 0:
                 if self.builder.config.plantuml_syntax_error_image:
-                    logger.warning('error while running plantuml\n\n%s' % serr)
+                    logger.warning(
+                        'error while running plantuml\n\n%s' % serr,
+                        location=node,
+                        type='plantuml',
+                    )
                 else:
                     raise PlantUmlError('error while running plantuml\n\n%s' % serr)
 
@@ -408,7 +414,9 @@ def _get_png_tag(self, fnames, node):
             (
                 'plantuml: unsupported scaling attributes: %s '
                 '(install PIL or Pillow)' % ', '.join(scale_attrs)
-            )
+            ),
+            location=node,
+            type='plantuml',
         )
     if not scale_attrs or Image is None:
         return '<img src="%s" alt="%s"/>\n' % (self.encode(refname), self.encode(alt))
@@ -441,7 +449,11 @@ def _get_png_tag(self, fnames, node):
                 for a, w in zip(['width', 'height'], im.size)
             )
         except (IOError, OSError) as err:
-            logger.warning('plantuml: failed to get image size: %s' % err)
+            logger.warning(
+                'plantuml: failed to get image size: %s' % err,
+                location=node,
+                type='plantuml',
+            )
 
     return '<a href="%s"><img src="%s" alt="%s" style="%s"/>' '</a>\n' % (
         self.encode(refname),
@@ -533,14 +545,14 @@ def _lookup_html_format(fmt):
 
 
 @contextmanager
-def _prepare_html_render(self, fmt):
+def _prepare_html_render(self, fmt, node):
     if fmt == 'none':
         raise nodes.SkipNode
 
     try:
         yield _lookup_html_format(fmt)
     except PlantUmlError as err:
-        logger.warning(str(err))
+        logger.warning(str(err), location=node, type='plantuml')
         raise nodes.SkipNode
 
 
@@ -551,7 +563,7 @@ def html_visit_plantuml(self, node):
     else:
         fmt = self.builder.config.plantuml_output_format
 
-    with _prepare_html_render(self, fmt) as (fileformats, gettag):
+    with _prepare_html_render(self, fmt, node) as (fileformats, gettag):
         # fnames: {fileformat: (refname, outfname), ...}
         fnames = dict((e, render_plantuml(self, node, e)) for e in fileformats)
 
@@ -647,7 +659,7 @@ def latex_visit_plantuml(self, node):
         refname, outfname = render_plantuml(self, node, fileformat)
         refname, outfname = postproc(self, refname, outfname)
     except PlantUmlError as err:
-        logger.warning(str(err))
+        logger.warning(str(err), location=node, type='plantuml')
         raise nodes.SkipNode
 
     if fmt == 'tikz':
@@ -711,7 +723,7 @@ def text_visit_plantuml(self, node):
     try:
         text = render_plantuml_inline(self, node, 'txt')
     except PlantUmlError as err:
-        logger.warning(str(err))
+        logger.warning(str(err), location=node, type='plantuml')
         text = node['uml']  # fall back to uml text, which is still readable
 
     self.new_state()
@@ -726,14 +738,18 @@ def pdf_visit_plantuml(self, node):
         refname, outfname = render_plantuml(self, node, 'eps')
         refname, outfname = _convert_eps_to_pdf(self, refname, outfname)
     except PlantUmlError as err:
-        logger.warning(str(err))
+        logger.warning(str(err), location=node, type='plantuml')
         raise nodes.SkipNode
     rep = nodes.image(uri=outfname, alt=node.get('alt', node['uml']))
     node.parent.replace(node, rep)
 
 
 def unsupported_visit_plantuml(self, node):
-    logger.warning('plantuml: unsupported output format (node skipped)')
+    logger.warning(
+        'plantuml: unsupported output format (node skipped)',
+        location=node,
+        type='plantuml',
+    )
     raise nodes.SkipNode