helper/schema: Read native maps from configuration

This adds a test and the support necessary to read from native maps
passed as variables via interpolation - for example:

```
resource ...... {
     mapValue = "${var.map}"
}
```

We also add support for interpolating maps from the flat-mapped resource
config, which is necessary to support assignment of computed maps, which
is now valid.

Unfortunately there is no good way to distinguish between a list and a
map in the flatmap. In lieu of changing that representation (which is
risky), we assume that if all the keys are numeric, this is intended to
be a list, and if not it is intended to be a map. This does preclude
maps which have purely numeric keys, which should be noted as a
backwards compatibility concern.

helper/schema/field_reader_config.go

@@ -100,7 +100,8 @@ func (r *ConfigFieldReader) readField(
 func (r *ConfigFieldReader) readMap(k string) (FieldReadResult, error) {
 	// We want both the raw value and the interpolated. We use the interpolated
 	// to store actual values and we use the raw one to check for
-	// computed keys.
+	// computed keys. Actual values are obtained in the switch, depending on
+	// the type of the raw value.
 	mraw, ok := r.Config.GetRaw(k)
 	if !ok {
 		return FieldReadResult{}, nil
@@ -109,6 +110,25 @@ func (r *ConfigFieldReader) readMap(k string) (FieldReadResult, error) {
 	result := make(map[string]interface{})
 	computed := false
 	switch m := mraw.(type) {
+	case string:
+		// This is a map which has come out of an interpolated variable, so we
+		// can just get the value directly from config. Values cannot be computed
+		// currently.
+		v, _ := r.Config.Get(k)
+
+		// If this isn't a map[string]interface, it must be computed.
+		mapV, ok := v.(map[string]interface{})
+		if !ok {
+			return FieldReadResult{
+				Exists:   true,
+				Computed: true,
+			}, nil
+		}
+
+		// Otherwise we can proceed as usual.
+		for i, iv := range mapV {
+			result[i] = iv
+		}
 	case []interface{}:
 		for i, innerRaw := range m {
 			for ik := range innerRaw.(map[string]interface{}) {

helper/schema/field_reader_config_test.go

@@ -183,6 +183,36 @@ func TestConfigFieldReader_ComputedMap(t *testing.T) {
 			}),
 			false,
 		},
+
+		"native map": {
+			[]string{"map"},
+			FieldReadResult{
+				Value: map[string]interface{}{
+					"bar": "baz",
+					"baz": "bar",
+				},
+				Exists:   true,
+				Computed: false,
+			},
+			testConfigInterpolate(t, map[string]interface{}{
+				"map": "${var.foo}",
+			}, map[string]ast.Variable{
+				"var.foo": ast.Variable{
+					Type: ast.TypeMap,
+					Value: map[string]ast.Variable{
+						"bar": ast.Variable{
+							Type:  ast.TypeString,
+							Value: "baz",
+						},
+						"baz": ast.Variable{
+							Type:  ast.TypeString,
+							Value: "bar",
+						},
+					},
+				},
+			}),
+			false,
+		},
 	}
 
 	for name, tc := range cases {

helper/schema/schema.go

@@ -19,8 +19,10 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/davecgh/go-spew/spew"
 	"github.com/hashicorp/terraform/terraform"
 	"github.com/mitchellh/mapstructure"
+	"log"
 )
 
 // Schema is used to describe the structure of a value.
@@ -1120,11 +1122,21 @@ func (m schemaMap) validateMap(
 	// case to []interface{} unless the slice is exactly that type.
 	rawV := reflect.ValueOf(raw)
 	switch rawV.Kind() {
+	case reflect.String:
+		// If raw and reified are equal, this is a string and should
+		// be rejected.
+		reified, reifiedOk := c.Get(k)
+		log.Printf("[jen20] reified: %s", spew.Sdump(reified))
+		log.Printf("[jen20]     raw: %s", spew.Sdump(raw))
+		if reifiedOk && raw == reified && !c.IsComputed(k) {
+			return nil, []error{fmt.Errorf("%s: should be a map", k)}
+		}
+		// Otherwise it's likely raw is an interpolation.
+		return nil, nil
 	case reflect.Map:
 	case reflect.Slice:
 	default:
-		return nil, []error{fmt.Errorf(
-			"%s: should be a map", k)}
+		return nil, []error{fmt.Errorf("%s: should be a map", k)}
 	}
 
 	// If it is not a slice, it is valid

terraform/interpolate.go

@@ -384,9 +384,9 @@ func (i *Interpolater) computeResourceVariable(
 		return &ast.Variable{Type: ast.TypeString, Value: attr}, nil
 	}
 
-	// computed list attribute
+	// computed list or map attribute
 	if _, ok := r.Primary.Attributes[v.Field+".#"]; ok {
-		variable, err := i.interpolateListAttribute(v.Field, r.Primary.Attributes)
+		variable, err := i.interpolateComplexTypeAttribute(v.Field, r.Primary.Attributes)
 		return &variable, err
 	}
 
@@ -513,7 +513,7 @@ func (i *Interpolater) computeResourceMultiVariable(
 		if !ok {
 			continue
 		}
-		multiAttr, err := i.interpolateListAttribute(v.Field, r.Primary.Attributes)
+		multiAttr, err := i.interpolateComplexTypeAttribute(v.Field, r.Primary.Attributes)
 		if err != nil {
 			return nil, err
 		}
@@ -559,12 +559,12 @@ func (i *Interpolater) computeResourceMultiVariable(
 	return &variable, err
 }
 
-func (i *Interpolater) interpolateListAttribute(
+func (i *Interpolater) interpolateComplexTypeAttribute(
 	resourceID string,
 	attributes map[string]string) (ast.Variable, error) {
 
 	attr := attributes[resourceID+".#"]
-	log.Printf("[DEBUG] Interpolating computed list attribute %s (%s)",
+	log.Printf("[DEBUG] Interpolating computed complex type attribute %s (%s)",
 		resourceID, attr)
 
 	// In Terraform's internal dotted representation of list-like attributes, the
@@ -575,18 +575,37 @@ func (i *Interpolater) interpolateListAttribute(
 		return unknownVariable(), nil
 	}
 
-	// Otherwise we gather the values from the list-like attribute and return
-	// them.
-	var members []string
-	numberedListMember := regexp.MustCompile("^" + resourceID + "\\.[0-9]+$")
-	for id, value := range attributes {
-		if numberedListMember.MatchString(id) {
-			members = append(members, value)
+	// At this stage we don't know whether the item is a list or a map, so we
+	// examine the keys to see whether they are all numeric.
+	var numericKeys []string
+	var allKeys []string
+	numberedListKey := regexp.MustCompile("^" + resourceID + "\\.[0-9]+$")
+	otherListKey := regexp.MustCompile("^" + resourceID + "\\.([^#]+)$")
+	for id, _ := range attributes {
+		if numberedListKey.MatchString(id) {
+			numericKeys = append(numericKeys, id)
+		}
+		if submatches := otherListKey.FindAllStringSubmatch(id, -1); len(submatches) > 0 {
+			allKeys = append(allKeys, submatches[0][1])
 		}
 	}
 
+	if len(numericKeys) == len(allKeys) {
+		// This is a list
+		var members []string
+		for _, key := range numericKeys {
+			members = append(members, attributes[key])
+		}
 		sort.Strings(members)
 		return hil.InterfaceToVariable(members)
+	} else {
+		// This is a map
+		members := make(map[string]interface{})
+		for _, key := range allKeys {
+			members[key] = attributes[resourceID+"."+key]
+		}
+		return hil.InterfaceToVariable(members)
+	}
 }
 
 func (i *Interpolater) resourceVariableInfo(