[filter] support Graphviz with panda

.gitignore

@@ -6,3 +6,4 @@ tmp-*
 tests/output/
 tests/*.bats.log
 missfont.log
+.panda

tests/extra.bats

@@ -322,6 +322,15 @@ teardown() {
           --output $OUT/$DIR/sample.pdf
 }
 
+## 58x: panda
+@test "581: A PDF file with graphviz images" {
+  DIR=panda
+  $PANDOC $IN/$DIR/graphviz.md \
+          --template=eisvogel \
+          --lua-filter=/panda.lua \
+          --output $OUT/$DIR/graphviz.pdf
+}
+
 ##
 ## 9xx: Other entrypoints
 ##

tests/input/panda/graphviz.md

@@ -0,0 +1,17 @@
+
+
+```{.dot render="{{dot}} "
+         img="panda_diagram_example"}
+digraph {
+    rankdir=LR;
+    input -> pandoc -> output
+    pandoc -> panda -> {pandoc, diagrams}
+    { rank=same; pandoc, panda }
+    { rank=same; diagrams, output }
+}
+```
+
+
+```{ render="{{dot}}"
+     include="tests/input/panda/hello.dot" }
+```

tests/input/panda/hello.dot

@@ -0,0 +1,4 @@
+digraph {
+    rankdir=LR;
+    Hello -> World;
+}

ubuntu/Dockerfile

@@ -52,6 +52,8 @@ RUN set -x && \
         unzip \
         # required for PDF meta analysis
         poppler-utils \
+        # for panda
+        graphviz \
     # clean up
     && apt-get clean && \
     rm -rf /var/lib/apt/lists/*