starlark/types: Resource.depends_on support

Signed-off-by: Máximo Cuadros <mcuadros@gmail.com>

starlark/types/hcl.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/hashicorp/hcl2/hcl"
+	"github.com/hashicorp/hcl2/hcl/hclsyntax"
 	"github.com/hashicorp/hcl2/hclwrite"
 	"github.com/zclconf/go-cty/cty"
 	"go.starlark.net/starlark"
@@ -69,12 +70,14 @@ func (r *Resource) ToHCL(b *hclwrite.Body) {
 	body := block.Body()
 
 	if r.parent.kind == ProviderKind {
-		body.SetAttributeTraversal("provider", hcl.Traversal{hcl.TraverseRoot{
-			Name: fmt.Sprintf("%s.%s", r.parent.typ, r.parent.Name()),
-		}})
+		body.SetAttributeTraversal("provider", hcl.Traversal{
+			hcl.TraverseRoot{Name: r.parent.typ},
+			hcl.TraverseAttr{Name: r.parent.Name()},
+		})
 	}
 
 	r.doToHCLAttributes(body)
+	r.doToHCLDependencies(body)
 }
 
 func (r *Resource) doToHCLAttributes(body *hclwrite.Body) {
@@ -84,11 +87,10 @@ func (r *Resource) doToHCLAttributes(body *hclwrite.Body) {
 			continue
 		}
 
-		// TODO(mcuadros): I don't know how to do this properly, meanwhile, this works.
 		if c, ok := v.v.(*Computed); ok {
-			body.SetAttributeTraversal(k, hcl.Traversal{hcl.TraverseRoot{
-				Name: c.String(),
-			}})
+			body.SetAttributeTraversal(k, hcl.Traversal{
+				hcl.TraverseRoot{Name: c.String()},
+			})
 
 			continue
 		}
@@ -107,3 +109,44 @@ func (r *Resource) doToHCLAttributes(body *hclwrite.Body) {
 		}
 	}
 }
+
+func (r *Resource) doToHCLDependencies(body *hclwrite.Body) {
+	if len(r.dependenies) == 0 {
+		return
+	}
+
+	toks := []*hclwrite.Token{}
+	toks = append(toks, &hclwrite.Token{
+		Type:  hclsyntax.TokenIdent,
+		Bytes: []byte("depends_on"),
+	})
+
+	toks = append(toks, &hclwrite.Token{
+		Type: hclsyntax.TokenEqual, Bytes: []byte{'='},
+	}, &hclwrite.Token{
+		Type: hclsyntax.TokenOBrack, Bytes: []byte{'['},
+	})
+
+	l := len(r.dependenies)
+	for i, dep := range r.dependenies {
+		name := fmt.Sprintf("%s.%s", dep.typ, dep.Name())
+		toks = append(toks, &hclwrite.Token{
+			Type: hclsyntax.TokenIdent, Bytes: []byte(name),
+		})
+
+		if i+1 == l {
+			break
+		}
+
+		toks = append(toks, &hclwrite.Token{
+			Type: hclsyntax.TokenComma, Bytes: []byte{','},
+		})
+	}
+
+	toks = append(toks, &hclwrite.Token{
+		Type: hclsyntax.TokenCBrack, Bytes: []byte{']'},
+	})
+
+	body.AppendUnstructuredTokens(toks)
+	body.AppendNewline()
+}

starlark/types/resource.go

@@ -37,8 +37,10 @@ type Resource struct {
 	typ    string
 	kind   Kind
 	block  *configschema.Block
-	parent *Resource
 	values map[string]*Value
+
+	parent      *Resource
+	dependenies []*Resource
 }
 
 // MakeResource returns a new resource of the given kind, type based on the
@@ -121,6 +123,8 @@ func (r *Resource) Hash() (uint32, error) {
 // Attr honors the starlark.HasAttrs interface.
 func (r *Resource) Attr(name string) (starlark.Value, error) {
 	switch name {
+	case "depends_on":
+		return starlark.NewBuiltin("depends_on", r.dependsOn), nil
 	case "__dict__":
 		return r.toDict(), nil
 	}
@@ -233,6 +237,25 @@ func (r *Resource) toDict() *starlark.Dict {
 	return d
 }
 
+func (r *Resource) dependsOn(_ *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, _ []starlark.Tuple) (starlark.Value, error) {
+	resources := make([]*Resource, len(args))
+	for i, arg := range args {
+		resource, ok := arg.(*Resource)
+		if !ok || resource.kind != DataSourceKind && resource.kind != ResourceKind {
+			return nil, fmt.Errorf("expected Resource<[data|resource].*>, got %s", arg.Type())
+		}
+
+		if r == resource {
+			return nil, fmt.Errorf("can't depend on itself")
+		}
+
+		resources[i] = resource
+	}
+
+	r.dependenies = append(r.dependenies, resources...)
+	return starlark.None, nil
+}
+
 // CompareSameType honors starlark.Comprable interface.
 func (x *Resource) CompareSameType(op syntax.Token, y_ starlark.Value, depth int) (bool, error) {
 	y := y_.(*Resource)

starlark/types/testdata/hcl.star

@@ -9,10 +9,12 @@ ubuntu.filter(name = "name", values = ["ubuntu/images/hvm-ssd/ubuntu-trusty-14.0
 ubuntu.filter(name = "virtualization-type", values = ["hvm"])
 ubuntu.owners = ["099720109477"]
 
+fedora = aws.data.ami("fedora")
 web = aws.resource.instance(instance_type = "t2.micro")
+web.depends_on(ubuntu, fedora)
 
-#web.instance_type = "t2.micro"
-#web.ami = ami.id
+web.instance_type = "t2.micro"
+web.ami = ubuntu.id
 
 template = aws.resource.launch_template()
 template.name_prefix = "example"

starlark/types/testdata/resource.star

@@ -125,4 +125,19 @@ assert.eq(disk.__dict__, {
         "size": 4194304,
         "label": "home"
     }]
-})
+})
+
+
+# depends_on
+userA = p.data.user()
+userB = p.data.user()
+userA.depends_on(userB)
+
+def dependsOnNonResource(): userA.depends_on(42)
+assert.fails(dependsOnNonResource, "expected Resource<\\[data|resource\\].\\*>, got int")
+
+def dependsOnNestedResource(): userA.depends_on(disk.partition())
+assert.fails(dependsOnNestedResource, "expected Resource<\\[data|resource\\].\\*>, got Resource<nested.partition>")
+
+def dependsOnItself(): userA.depends_on(userA)
+assert.fails(dependsOnItself, "can't depend on itself")