Fail on output(depended-by relationship in a DAG) from an undefined node

pkg/dag/dag.go

@@ -30,19 +30,32 @@ type DAG struct {
 	cap       int
 	initNodes []string
 
-	nodes     []string
-	outputs   map[string]map[string]bool
-	labels    map[string]map[string]bool
+	nodes []string
+	// a.k.a dependents of the node denoted by the key
+	// `outputs["api"]["web"] = true` means api's sole dependent is "web"
+	// i.e. "web" depends on "api"
+	outputs map[string]map[string]bool
+	labels  map[string]map[string]bool
+	// a.k.a number of dependenciesthat the node denoted by the key has.
+	// `numInputs["web"] = 2` means "web" has 2 dependencies.
 	numInputs map[string]int
 }
 
 func (g *DAG) AddNode(name string) bool {
-	if _, ok := g.outputs[name]; ok {
+	if _, ok := g.numInputs[name]; ok {
 		return false
 	}
+
 	g.nodes = append(g.nodes, name)
-	g.outputs[name] = make(map[string]bool)
-	g.numInputs[name] = 0
+
+	if _, ok := g.outputs[name]; !ok {
+		g.outputs[name] = make(map[string]bool)
+	}
+
+	if _, ok := g.numInputs[name]; ok {
+		g.numInputs[name] = 0
+	}
+
 	return true
 }
 
@@ -76,7 +89,8 @@ func (g *DAG) AddNodes(names ...string) bool {
 func (g *DAG) AddEdge(from, to string) bool {
 	m, ok := g.outputs[from]
 	if !ok {
-		return false
+		m = map[string]bool{}
+		g.outputs[from] = m
 	}
 
 	m[to] = true
@@ -140,10 +154,6 @@ func (g *DAG) Add(node string, opt ...AddOption) bool {
 
 	g.AddNode(node)
 
-	for _, d := range opts.deps {
-		g.Add(d)
-	}
-
 	deps := g.AddDependencies(node, opts.deps)
 
 	g.AddLabels(node, opts.labels)
@@ -244,6 +254,15 @@ func (e *Error) Error() string {
 	return fmt.Sprintf("cycle detected: %v", e.Cycle)
 }
 
+type UndefinedDependencyError struct {
+	UndefinedNode string
+	Dependents    []string
+}
+
+func (e *UndefinedDependencyError) Error() string {
+	return fmt.Sprintf("undefined node %q is depended by node(s): %s", e.UndefinedNode, strings.Join(e.Dependents, ", "))
+}
+
 type UnhandledDependencyError struct {
 	UnhandledDependencies []UnhandledDependency
 }
@@ -367,6 +386,19 @@ func (g *DAG) Sort(opts ...SortOption) (Topology, error) {
 		}
 	}
 
+	for dep, dependents := range outputs {
+		if _, ok := nodes[dep]; !ok {
+			var dependentsNames []string
+			for d := range dependents {
+				dependentsNames = append(dependentsNames, d)
+			}
+			return nil, &UndefinedDependencyError{
+				UndefinedNode: dep,
+				Dependents:    dependentsNames,
+			}
+		}
+	}
+
 	// We sort sets of nodes rather than nodes themselves,
 	// so that we know which items can be processed in parallel in the DAG
 	// See https://cs.stackexchange.com/questions/2524/getting-parallel-items-in-dependency-resolution

pkg/dag/dag_test.go

@@ -2,6 +2,7 @@ package dag
 
 import (
 	"bytes"
+	"fmt"
 	"log"
 	"testing"
 )
@@ -94,6 +95,8 @@ func TestDAG_DagCleanAPI(t *testing.T) {
 	g2.Add("api", Dependencies([]string{"db", "cache", "net"}))
 	g2.Add("db", Dependencies([]string{"net"}))
 	g2.Add("mesh", Dependencies([]string{"net"}))
+	g2.Add("net")
+	g2.Add("cache")
 
 	res, err := g2.Plan()
 	if err != nil {
@@ -291,6 +294,8 @@ func TestDAG_Dag_Dot(t *testing.T) {
 	g2.Add("release/api", Dependencies([]string{"release/db", "release/cache", "release/net"}), Labels([]string{"tier:api"}))
 	g2.Add("release/db", Dependencies([]string{"release/net"}), Labels([]string{"tier:db"}))
 	g2.Add("release/mesh", Dependencies([]string{"release/net"}), Labels([]string{"tier:net"}))
+	g2.Add("release/net")
+	g2.Add("release/cache")
 
 	w := &bytes.Buffer{}
 
@@ -365,3 +370,27 @@ func TestDAG_GraphAPICycle(t *testing.T) {
 		t.Errorf("unexpected result: expected=%q, got=%q", expected, actual)
 	}
 }
+
+func TestDAG_UndefinedDependency_MaybeTypo(t *testing.T) {
+	g2 := New()
+	g2.Add(
+		"web",
+		Dependencies([]string{
+			"ok",
+			"ng",
+		}),
+	)
+	g2.Add(
+		"ok",
+	)
+
+	_, err := g2.Plan()
+
+	if err == nil {
+		t.Fatalf("expected error didnt occur")
+	}
+
+	if fmt.Sprintf("%v", err) != `undefined node "ng" is depended by node(s): web` {
+		t.Fatalf("%v", err)
+	}
+}