graph/encoding/dot: allow unmarshaling of global attributes

graph/encoding/dot/decode.go

@@ -25,6 +25,13 @@ type Builder interface {
 	NewEdge(from, to graph.Node) graph.Edge
 }
 
+// UnmashalerAttrs is implemented by graph values that can unmarshal global
+// DOT attributes.
+type UnmarshalerAttrs interface {
+	// DOTUnmarshalerAttrs returns the global attribute unmarshalers.
+	DOTUnmarshalerAttrs() (graph, node, edge UnmarshalerAttr)
+}
+
 // UnmarshalerAttr is implemented by types that can unmarshal a DOT
 // attribute description of themselves.
 type UnmarshalerAttr interface {
@@ -60,6 +67,9 @@ func copyGraph(dst Builder, src *ast.Graph) (err error) {
 		directed: src.Directed,
 		ids:      make(map[string]graph.Node),
 	}
+	if a, ok := dst.(UnmarshalerAttrs); ok {
+		gen.graphAttr, gen.nodeAttr, gen.edgeAttr = a.DOTUnmarshalerAttrs()
+	}
 	for _, stmt := range src.Stmts {
 		gen.addStmt(dst, stmt)
 	}
@@ -79,6 +89,8 @@ type generator struct {
 	// Stack of start indices into the subgraph node slice. The top element
 	// corresponds to the start index of the active (or inner-most) subgraph.
 	subStart []int
+	// graph, node and edge are top-level graph attributes.
+	graphAttr, nodeAttr, edgeAttr UnmarshalerAttr
 }
 
 // node returns the gonum node corresponding to the given dot AST node ID,
@@ -119,7 +131,39 @@ func (gen *generator) addStmt(dst Builder, stmt ast.Stmt) {
 	case *ast.EdgeStmt:
 		gen.addEdgeStmt(dst, stmt)
 	case *ast.AttrStmt:
-		// ignore.
+		var n UnmarshalerAttr
+		var dst string
+		switch stmt.Kind {
+		case ast.KindGraph:
+			if gen.graphAttr == nil {
+				return
+			}
+			n = gen.graphAttr
+			dst = "graph"
+		case ast.KindNode:
+			if gen.nodeAttr == nil {
+				return
+			}
+			n = gen.nodeAttr
+			dst = "node"
+		case ast.KindEdge:
+			if gen.edgeAttr == nil {
+				return
+			}
+			n = gen.edgeAttr
+			dst = "edge"
+		default:
+			panic("unreachable")
+		}
+		for _, attr := range stmt.Attrs {
+			a := Attribute{
+				Key:   attr.Key,
+				Value: attr.Val,
+			}
+			if err := n.UnmarshalDOTAttr(a); err != nil {
+				panic(fmt.Errorf("unable to unmarshal global %s DOT attribute (%s=%s)", dst, a.Key, a.Value))
+			}
+		}
 	case *ast.Attr:
 		// ignore.
 	case *ast.Subgraph:

graph/encoding/dot/decode_test.go

@@ -45,13 +45,25 @@ func TestRoundTrip(t *testing.T) {
 		}
 		got := string(buf)
 		if got != g.want {
-			t.Errorf("i=%d: graph content mismatch; expected `%s`, got `%s`", i, g.want, got)
+			t.Errorf("i=%d: graph content mismatch; want:\n%s\n\ngot:\n%s", i, g.want, got)
 			continue
 		}
 	}
 }
 
 const directed = `digraph {
+	graph [
+		outputorder=edgesfirst
+	];
+	node [
+		shape=circle
+		style=filled
+	];
+	edge [
+		penwidth=5
+		color=gray
+	];
+
 	// Node definitions.
 	0 [label="foo 2"];
 	1 [label="bar 2"];
@@ -61,6 +73,18 @@ const directed = `digraph {
 }`
 
 const undirected = `graph {
+	graph [
+		outputorder=edgesfirst
+	];
+	node [
+		shape=circle
+		style=filled
+	];
+	edge [
+		penwidth=5
+		color=gray
+	];
+
 	// Node definitions.
 	0 [label="foo 2"];
 	1 [label="bar 2"];
@@ -79,6 +103,7 @@ const undirected = `graph {
 // dotDirectedGraph implements the dot.Builder interface.
 type dotDirectedGraph struct {
 	*simple.DirectedGraph
+	graph, node, edge attributes
 }
 
 // newDotDirectedGraph returns a new directed capable of creating user-defined
@@ -105,12 +130,23 @@ func (g *dotDirectedGraph) NewEdge(from, to graph.Node) graph.Edge {
 	return e
 }
 
+// DOTAttributers implements the dot.Attributers interface.
+func (g *dotDirectedGraph) DOTAttributers() (graph, node, edge Attributer) {
+	return g.graph, g.node, g.edge
+}
+
+// DOTUnmarshalerAttrs implements the dot.UnmarshalerAttrs interface.
+func (g *dotDirectedGraph) DOTUnmarshalerAttrs() (graph, node, edge UnmarshalerAttr) {
+	return &g.graph, &g.node, &g.edge
+}
+
 // dotUndirectedGraph extends simple.UndirectedGraph to add NewNode and NewEdge
 // methods for creating user-defined nodes and edges.
 //
 // dotUndirectedGraph implements the dot.Builder interface.
 type dotUndirectedGraph struct {
 	*simple.UndirectedGraph
+	graph, node, edge attributes
 }
 
 // newDotUndirectedGraph returns a new undirected capable of creating user-
@@ -137,6 +173,16 @@ func (g *dotUndirectedGraph) NewEdge(from, to graph.Node) graph.Edge {
 	return e
 }
 
+// DOTAttributers implements the dot.Attributers interface.
+func (g *dotUndirectedGraph) DOTAttributers() (graph, node, edge Attributer) {
+	return g.graph, g.node, g.edge
+}
+
+// DOTUnmarshalerAttrs implements the dot.UnmarshalerAttrs interface.
+func (g *dotUndirectedGraph) DOTUnmarshalerAttrs() (graph, node, edge UnmarshalerAttr) {
+	return &g.graph, &g.node, &g.edge
+}
+
 // dotNode extends simple.Node with a label field to test round-trip encoding
 // and decoding of node DOT label attributes.
 type dotNode struct {
@@ -194,3 +240,14 @@ func (e *dotEdge) DOTAttributes() []Attribute {
 	}
 	return []Attribute{attr}
 }
+
+// attributes is a helper for global attributes.
+type attributes []Attribute
+
+func (a attributes) DOTAttributes() []Attribute {
+	return []Attribute(a)
+}
+func (a *attributes) UnmarshalDOTAttr(attr Attribute) error {
+	*a = append(*a, attr)
+	return nil
+}