Handling default attributes for node/edge/graph statements

src/dot.js

@@ -30,24 +30,57 @@ dagre.dot.toGraph = function(str) {
     g.addEdge(id, source, target, edge);
   }
 
-  function handleStmt(stmt) {
+  var defaultAttrs = {
+    _default: {},
+
+    get: function get(type, attrs) {
+      if (typeof this._default[type] !== "undefined") {
+        var mergedAttrs = {};
+        // clone default attributes so they won't get overwritten in the next step
+        mergeAttributes(this._default[type], mergedAttrs);
+        // merge statement attributes with default attributes, precedence give to stmt attributes
+        mergeAttributes(attrs, mergedAttrs);
+        return mergedAttrs;
+      } else {
+        return attrs;
+      }
+    },
+
+    set: function set(type, attrs) {
+      this._default[type] = this.get(type, attrs);
+    }
+  };
+
+  function handleStmt(stmt, skipDefaultAttributes) {
+    var attrs;
+    if (typeof skipDefaultAttributes === "undefined" || skipDefaultAttributes !== true) {
+       attrs = defaultAttrs.get(stmt.type, stmt.attrs);
+    } else {
+      attrs = stmt.attrs;
+    }
+
     switch (stmt.type) {
       case "node":
-        createNode(stmt.id, stmt.attrs);
+        createNode(stmt.id, attrs);
         break;
       case "edge":
         var prev;
         stmt.elems.forEach(function(elem) {
-          handleStmt(elem);
+          // Default attribute inclusion has to be skipped for nested calls
+          // to not overwrite attributes that have been defined through preceding
+          // default attribute statements.
+          // 
+          // Test "overrides redefined default attributes" in test/dot-test.js checks that.
+          handleStmt(elem, true);
 
           switch(elem.type) {
             case "node":
               var curr = elem.id;
 
               if (prev) {
-                createEdge(prev, curr, stmt.attrs);
+                createEdge(prev, curr, attrs);
                 if (undir) {
-                  createEdge(curr, prev, stmt.attrs);
+                  createEdge(curr, prev, attrs);
                 }
               }
               prev = curr;
@@ -59,7 +92,7 @@ dagre.dot.toGraph = function(str) {
         });
         break;
       case "attr":
-        // Ignore for now
+        defaultAttrs.set(stmt.attrType, stmt.attrs);
         break;
       default:
         throw new Error("Unsupported statement type: " + stmt.type);

test/dot-test.js

@@ -3,4 +3,49 @@ describe("dagre.dot.toGraph", function() {
     var g = dagre.dot.toGraph("digraph { a [label=\"\"]; }");
     assert.equal(g.node("a").label, "");
   });
+  it("adds default attributes to nodes", function() {
+    var dot = "digraph { node [color=black shape=box]; n1 [label=\"n1\"]; n2 [label=\"n2\"]; n1 -> n2; }";
+    var g = dagre.dot.toGraph(dot);
+    assert.equal(g.node("n1").color, "black");
+    assert.equal(g.node("n1").shape, "box");
+    assert.equal(g.node("n1").label, "n1");
+
+    assert.equal(g.node("n2").color, "black");
+    assert.equal(g.node("n2").shape, "box");
+    assert.equal(g.node("n2").label, "n2");    
+  });
+  it("combines multiple default attribute statements", function() {
+    var dot = "digraph { node [color=black]; node [shape=box]; n1 [label=\"n1\"]; }";
+    var g = dagre.dot.toGraph(dot);
+    assert.equal(g.node("n1").color, "black");
+    assert.equal(g.node("n1").shape, "box");
+  });
+  it("takes statement order into account when applying default attributes", function() {
+    var dot = "digraph { node [color=black]; n1 [label=\"n1\"]; node [shape=box]; n2 [label=\"n2\"]; }";
+    var g = dagre.dot.toGraph(dot);
+    assert.equal(g.node("n1").color, "black");
+    assert.equal(g.node("n1").shape, undefined);
+
+    assert.equal(g.node("n2").color, "black");
+    assert.equal(g.node("n2").shape, "box");
+  });
+  it("overrides redefined default attributes", function() {
+    var dot = "digraph { node [color=black]; n1 [label=\"n1\"]; node [color=green]; n2 [label=\"n2\"]; n1 -> n2; }";
+    var g = dagre.dot.toGraph(dot);
+    assert.equal(g.node("n1").color, "black");
+    assert.equal(g.node("n2").color, "green");
+
+    // Implementation detail:
+    // toGraph::handleStmt wants to assure that nodes used in an edge definition
+    // are defined by calling createNode for those nodes. If these nested createNode
+    // calls don't skip merging the default attributes, the attributes of already
+    // defined nodes could be overwritten, causing both nodes in this test case to
+    // have "color" set to green. 
+  });
+  it("does not carry attributes from one node over to the next", function() {
+    var dot = "digraph { node [color=black]; n1 [label=\"n1\" fontsize=12]; n2 [label=\"n2\"]; n1 -> n2; }";
+    var g = dagre.dot.toGraph(dot);
+    assert.equal(g.node("n1").fontsize, 12);
+    assert.equal(g.node("n2").fontsize, undefined, "n2.fontsize should not be defined");
+  });
 });