entc/gen: reject codegen in case of duplicate edges (#858)

See #856

entc/gen/graph.go

@@ -200,9 +200,13 @@ func (g *Graph) addIndexes(schema *load.Schema) {
 // addEdges adds the node edges to the graph.
 func (g *Graph) addEdges(schema *load.Schema) {
 	t, _ := g.typ(schema.Name)
+	seen := make(map[string]struct{}, len(schema.Edges))
 	for _, e := range schema.Edges {
 		typ, ok := g.typ(e.Type)
 		expect(ok, "type %q does not exist for edge", e.Type)
+		_, ok = seen[e.Name]
+		expect(!ok, "%s schema contains multiple %q edges", schema.Name, e.Name)
+		seen[e.Name] = struct{}{}
 		switch {
 		// Assoc only.
 		case !e.Inverse:

entc/gen/graph_test.go

@@ -178,6 +178,25 @@ func TestNewGraphBadInverse(t *testing.T) {
 	require.Errorf(t, err, "mismatch type for back-reference")
 }
 
+func TestNewGraphDuplicateEdges(t *testing.T) {
+	_, err := NewGraph(&Config{Package: "entc/gen", Storage: drivers[0]},
+		&load.Schema{
+			Name: "User",
+			Edges: []*load.Edge{
+				{Name: "groups", Type: "Group"},
+				{Name: "groups", Type: "Group", RefName: "owner", Inverse: true},
+			},
+		},
+		&load.Schema{
+			Name: "Group",
+			Edges: []*load.Edge{
+				{Name: "users", Type: "User", RefName: "groups", Inverse: true},
+				{Name: "owner", Type: "User", Unique: true},
+			},
+		})
+	require.EqualError(t, err, `entc/gen: User schema contains multiple "groups" edges`)
+}
+
 func TestRelation(t *testing.T) {
 	require := require.New(t)
 	_, err := NewGraph(&Config{Package: "entc/gen", Storage: drivers[0]}, T1)

entc/gen/type.go

@@ -239,11 +239,11 @@ func (t Type) Receiver() string {
 	return receiver(t.Name)
 }
 
-// HasAssoc returns true if this type has an assoc edge with the given name.
-// faster than map access for most cases.
+// HasAssoc returns true if this type has an assoc-edge (non-inverse)
+// with the given name. faster than map access for most cases.
 func (t Type) HasAssoc(name string) (*Edge, bool) {
 	for _, e := range t.Edges {
-		if name == e.Name {
+		if name == e.Name && !e.IsInverse() {
 			return e, true
 		}
 	}