feat(GraphViz): Add basic error handling

Signed-off-by: Gordon Smith <gordonjsmith@gmail.com>

.travis.yml

@@ -14,5 +14,6 @@ install:
   - npm run install-prerequisites
   - npm run install-build-deps
 before_script:
-  - npm run lint;
-  - npm run build;
+  - npm run lint
+  - npm run dev-start &
+  - npm run build

cpp/graphviz/graphvizlib/main.cpp

@@ -21,6 +21,7 @@ char *vizLastErrorMessage()
 
 const char *Main::layout(const char *src, const char *format, const char *engine)
 {
+    errorMessage = NULL;
     char *result = NULL;
     GVC_t *context;
     Agraph_t *graph;
@@ -53,6 +54,11 @@ const char *Main::layout(const char *src, const char *format, const char *engine
     return result;
 }
 
+const char *Main::lastError()
+{
+    return errorMessage;
+}
+
 //  Patch for invalid osage function  ---
 //  https://gitlab.com/graphviz/graphviz/issues/1544
 #include "types.h"

cpp/graphviz/graphvizlib/main.hpp

@@ -2,4 +2,5 @@ class Main
 {
 public:
     static const char *layout(const char *dot, const char *format, const char *engine);
+    static const char *lastError();
 };

cpp/graphviz/graphvizlib/main.idl

@@ -1,3 +1,4 @@
 interface Main {
   [Const] static DOMString layout([Const] DOMString dot, [Const] DOMString format, [Const] DOMString engine);
+  [Const] static DOMString lastError();
 };

index.html

@@ -60,16 +60,20 @@ <h3>End</h3>
         hpccWasm.graphviz.layout(dot, "svg", "dot").then(svg => {
             const div = document.getElementById("placeholder");
             div.innerHTML = svg;
-        });
+        }).catch(err => console.error(err.message));
 
         hpccWasm.graphviz.layout(dot, "svg", "dot").then(svg => {
             const div = document.getElementById("placeholder2");
             div.innerHTML = svg;
-        });
+        }).catch(err => console.error(err.message));
 
         hpccWasm.graphvizSync().then(graphviz => {
             const div = document.getElementById("placeholder3");
-            div.innerHTML = graphviz.layout(dot, "svg", "dot");
+            try {
+                div.innerHTML = graphviz.layout(dot, "svg", "dot");
+            } catch (e) {
+                div.innerHTML = e.message;
+            }
         });
     </script>