fix layout option & check sourcefile exists

sphinx_d2lang/d2lang.py

@@ -4,6 +4,7 @@ from docutils.parsers.rst import Directive, directives
 from sphinx.util.docutils import SphinxDirective
 
 from shutil import which
+from pathlib import Path
 import shlex
 import subprocess
 import tempfile
@@ -24,12 +25,16 @@ class D2langDirective(SphinxDirective):
             output_fname = self.options.get('filename')
         else:
             output_fname = 'test.svg'
-        if 'layout':
+        if 'layout' in self.options:
             layout = self.options.get('layout')
         else:
             layout = 'dagre'
         if self.arguments:
+            path = Path(srcdir + self.arguments[0])
+            if path.is_file():
                 build_svg(self.arguments[0], srcdir, output_fname, layout)
+            else:
+                raise
         else:
             with tempfile.NamedTemporaryFile() as fp:
                 for line in self.content.data: