terraform: update interpolation to be more flexible w/o config

terraform/context.go

@@ -229,6 +229,21 @@ func (c *Context) ShadowError() error {
 	return c.shadowErr
 }
 
+// Interpolater returns an Interpolater built on a copy of the state
+// that can be used to test interpolation values.
+func (c *Context) Interpolater() *Interpolater {
+	var varLock sync.Mutex
+	var stateLock sync.RWMutex
+	return &Interpolater{
+		Operation:          walkApply,
+		Module:             c.module,
+		State:              c.state.DeepCopy(),
+		StateLock:          &stateLock,
+		VariableValues:     map[string]interface{}{},
+		VariableValuesLock: &varLock,
+	}
+}
+
 // Input asks for input to fill variables and provider configurations.
 // This modifies the configuration in-place, so asking for Input twice
 // may result in different UI output showing different current values.

terraform/interpolate.go

@@ -46,6 +46,10 @@ type InterpolationScope struct {
 func (i *Interpolater) Values(
 	scope *InterpolationScope,
 	vars map[string]config.InterpolatedVariable) (map[string]ast.Variable, error) {
+	if scope == nil {
+		scope = &InterpolationScope{}
+	}
+
 	result := make(map[string]ast.Variable, len(vars))
 
 	// Copy the default variables
@@ -369,7 +373,12 @@ func (i *Interpolater) computeResourceVariable(
 	// If we're requesting "count" its a special variable that we grab
 	// directly from the config itself.
 	if v.Field == "count" {
-		count, err := cr.Count()
+		var count int
+		if cr != nil {
+			count, err = cr.Count()
+		} else {
+			count, err = i.resourceCountMax(module, cr, v)
+		}
 		if err != nil {
 			return nil, fmt.Errorf(
 				"Error reading %s count: %s",
@@ -380,26 +389,36 @@ func (i *Interpolater) computeResourceVariable(
 		return &ast.Variable{Type: ast.TypeInt, Value: count}, nil
 	}
 
-	// If we have no module in the state yet or count, return empty
-	if module == nil || len(module.Resources) == 0 {
-		return nil, nil
-	}
-
 	// Get the resource out from the state. We know the state exists
 	// at this point and if there is a state, we expect there to be a
 	// resource with the given name.
-	r, ok := module.Resources[id]
-	if !ok && v.Multi && v.Index == 0 {
-		r, ok = module.Resources[v.ResourceId()]
-	}
-	if !ok {
-		r = nil
-	}
-	if r == nil {
-		goto MISSING
+	var r *ResourceState
+	if module != nil && len(module.Resources) > 0 {
+		var ok bool
+		r, ok = module.Resources[id]
+		if !ok && v.Multi && v.Index == 0 {
+			r, ok = module.Resources[v.ResourceId()]
+		}
+		if !ok {
+			r = nil
+		}
 	}
+	if r == nil || r.Primary == nil {
+		if i.Operation == walkApply || i.Operation == walkPlan {
+			return nil, fmt.Errorf(
+				"Resource '%s' not found for variable '%s'",
+				v.ResourceId(),
+				v.FullKey())
+		}
+
+		// If we have no module in the state yet or count, return empty.
+		// NOTE(@mitchellh): I actually don't know why this is here. During
+		// a refactor I kept this here to maintain the same behavior, but
+		// I'm not sure why its here.
+		if module == nil || len(module.Resources) == 0 {
+			return nil, nil
+		}
 
-	if r.Primary == nil {
 		goto MISSING
 	}
 
@@ -672,12 +691,6 @@ func (i *Interpolater) resourceVariableInfo(
 			break
 		}
 	}
-	if cr == nil {
-		return nil, nil, fmt.Errorf(
-			"Resource '%s' not found for variable '%s'",
-			v.ResourceId(),
-			v.FullKey())
-	}
 
 	// Get the relevant module
 	module := i.State.ModuleByPath(scope.Path)