terraform: test path variables

config/interpolate.go

@@ -86,7 +86,9 @@ type PathValueType byte
 
 const (
 	PathValueInvalid PathValueType = iota
+	PathValueCwd
 	PathValueModule
+	PathValueRoot
 )
 
 // A ResourceVariable is a variable that is referencing the field
@@ -226,8 +228,12 @@ func NewPathVariable(key string) (*PathVariable, error) {
 	var fieldType PathValueType
 	parts := strings.SplitN(key, ".", 2)
 	switch parts[1] {
+	case "cwd":
+		fieldType = PathValueCwd
 	case "module":
 		fieldType = PathValueModule
+	case "root":
+		fieldType = PathValueRoot
 	}
 
 	return &PathVariable{

terraform/context.go

@@ -3,6 +3,7 @@ package terraform
 import (
 	"fmt"
 	"log"
+	"os"
 	"sort"
 	"strconv"
 	"strings"
@@ -54,7 +55,7 @@ type ContextOpts struct {
 	Provisioners map[string]ResourceProvisionerFactory
 	Variables    map[string]string
 
-	UIInput  UIInput
+	UIInput UIInput
 }
 
 // NewContext creates a new context.
@@ -1437,6 +1438,24 @@ func (c *walkContext) computeVars(
 			}
 
 			vs[n] = value
+		case *config.PathVariable:
+			switch v.Type {
+			case config.PathValueCwd:
+				wd, err := os.Getwd()
+				if err != nil {
+					return fmt.Errorf(
+						"Couldn't get cwd for var %s: %s",
+						v.FullKey(), err)
+				}
+
+				vs[n] = wd
+			case config.PathValueModule:
+				if t := c.Context.module.Child(c.Path[1:]); t != nil {
+					vs[n] = t.Config().Dir
+				}
+			case config.PathValueRoot:
+				vs[n] = c.Context.module.Config().Dir
+			}
 		case *config.ResourceVariable:
 			var attr string
 			var err error

terraform/context_test.go

@@ -2,6 +2,7 @@ package terraform
 
 import (
 	"fmt"
+	"os"
 	"reflect"
 	"sort"
 	"strings"
@@ -2822,6 +2823,43 @@ func TestContextPlan_moduleDestroy(t *testing.T) {
 	}
 }
 
+func TestContextPlan_pathVar(t *testing.T) {
+	cwd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	m := testModule(t, "plan-path-var")
+	p := testProvider("aws")
+	p.DiffFn = testDiffFn
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+	})
+
+	plan, err := ctx.Plan(nil)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(plan.String())
+	expected := strings.TrimSpace(testTerraformPlanPathVarStr)
+
+	// Warning: this ordering REALLY matters for this test. The
+	// order is: cwd, module, root.
+	expected = fmt.Sprintf(
+		expected,
+		cwd,
+		m.Config().Dir,
+		m.Config().Dir)
+
+	if actual != expected {
+		t.Fatalf("bad:\n%s\n\nexpected:\n\n%s", actual, expected)
+	}
+}
+
 func TestContextPlan_diffVar(t *testing.T) {
 	m := testModule(t, "plan-diffvar")
 	p := testProvider("aws")

terraform/terraform_test.go

@@ -875,3 +875,18 @@ STATE:
 
 <no state>
 `
+
+const testTerraformPlanPathVarStr = `
+DIFF:
+
+CREATE: aws_instance.foo
+  cwd:    "" => "%s/barpath"
+  module: "" => "%s/foopath"
+  root:   "" => "%s/barpath"
+  type:   "" => "aws_instance"
+
+STATE:
+
+<no state>
+`
+

terraform/test-fixtures/plan-path-var/main.tf

@@ -0,0 +1,5 @@
+resource "aws_instance" "foo" {
+    cwd = "${path.cwd}/barpath"
+    module = "${path.module}/foopath"
+    root = "${path.root}/barpath"
+}