config: parsing of "locals" blocks in configuration

config/config.go

@@ -34,6 +34,7 @@ type Config struct {
 	ProviderConfigs []*ProviderConfig
 	Resources       []*Resource
 	Variables       []*Variable
+	Locals          []*Local
 	Outputs         []*Output
 
 	// The fields below can be filled in by loaders for validation
@@ -147,7 +148,7 @@ func (p *Provisioner) Copy() *Provisioner {
 	}
 }
 
-// Variable is a variable defined within the configuration.
+// Variable is a module argument defined within the configuration.
 type Variable struct {
 	Name         string
 	DeclaredType string `mapstructure:"type"`
@@ -155,6 +156,12 @@ type Variable struct {
 	Description  string
 }
 
+// Local is a local value defined within the configuration.
+type Local struct {
+	Name      string
+	RawConfig *RawConfig
+}
+
 // Output is an output defined within the configuration. An output is
 // resulting data that is highlighted by Terraform when finished. An
 // output marked Sensitive will be output in a masked form following
@@ -680,6 +687,29 @@ func (c *Config) Validate() error {
 		}
 	}
 
+	// Check that all locals are valid
+	{
+		found := make(map[string]struct{})
+		for _, l := range c.Locals {
+			if _, ok := found[l.Name]; ok {
+				errs = append(errs, fmt.Errorf(
+					"%s: duplicate local. local value names must be unique",
+					l.Name,
+				))
+				continue
+			}
+			found[l.Name] = struct{}{}
+
+			for _, v := range l.RawConfig.Variables {
+				if _, ok := v.(*CountVariable); ok {
+					errs = append(errs, fmt.Errorf(
+						"local %s: count variables are only valid within resources", l.Name,
+					))
+				}
+			}
+		}
+	}
+
 	// Check that all outputs are valid
 	{
 		found := make(map[string]struct{})

config/config_string.go

@@ -148,6 +148,42 @@ func outputsStr(os []*Output) string {
 	return strings.TrimSpace(result)
 }
 
+func localsStr(ls []*Local) string {
+	ns := make([]string, 0, len(ls))
+	m := make(map[string]*Local)
+	for _, l := range ls {
+		ns = append(ns, l.Name)
+		m[l.Name] = l
+	}
+	sort.Strings(ns)
+
+	result := ""
+	for _, n := range ns {
+		l := m[n]
+
+		result += fmt.Sprintf("%s\n", n)
+
+		if len(l.RawConfig.Variables) > 0 {
+			result += fmt.Sprintf("  vars\n")
+			for _, rawV := range l.RawConfig.Variables {
+				kind := "unknown"
+				str := rawV.FullKey()
+
+				switch rawV.(type) {
+				case *ResourceVariable:
+					kind = "resource"
+				case *UserVariable:
+					kind = "user"
+				}
+
+				result += fmt.Sprintf("    %s: %s\n", kind, str)
+			}
+		}
+	}
+
+	return strings.TrimSpace(result)
+}
+
 // This helper turns a provider configs field into a deterministic
 // string value for comparison in tests.
 func providerConfigsStr(pcs []*ProviderConfig) string {

config/loader_hcl.go

@@ -37,6 +37,7 @@ func (t *hclConfigurable) Config() (*Config, error) {
 	validKeys := map[string]struct{}{
 		"atlas":     struct{}{},
 		"data":      struct{}{},
+		"locals":    struct{}{},
 		"module":    struct{}{},
 		"output":    struct{}{},
 		"provider":  struct{}{},
@@ -72,6 +73,15 @@ func (t *hclConfigurable) Config() (*Config, error) {
 		}
 	}
 
+	// Build local values
+	if locals := list.Filter("locals"); len(locals.Items) > 0 {
+		var err error
+		config.Locals, err = loadLocalsHcl(locals)
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	// Get Atlas configuration
 	if atlas := list.Filter("atlas"); len(atlas.Items) > 0 {
 		var err error
@@ -408,6 +418,59 @@ func loadModulesHcl(list *ast.ObjectList) ([]*Module, error) {
 	return result, nil
 }
 
+// loadLocalsHcl recurses into the given HCL object turns it into
+// a list of locals.
+func loadLocalsHcl(list *ast.ObjectList) ([]*Local, error) {
+
+	result := make([]*Local, 0, len(list.Items))
+
+	for _, block := range list.Items {
+		if len(block.Keys) > 0 {
+			return nil, fmt.Errorf(
+				"locals block at %s should not have label %q",
+				block.Pos(), block.Keys[0].Token.Value(),
+			)
+		}
+
+		blockObj, ok := block.Val.(*ast.ObjectType)
+		if !ok {
+			return nil, fmt.Errorf("locals value at %s should be a block", block.Val.Pos())
+		}
+
+		// blockObj now contains directly our local decls
+		for _, item := range blockObj.List.Items {
+			if len(item.Keys) != 1 {
+				return nil, fmt.Errorf("local declaration at %s may not be a block", item.Val.Pos())
+			}
+
+			// By the time we get here there can only be one item left, but
+			// we'll decode into a map anyway because it's a convenient way
+			// to extract both the key and the value robustly.
+			kv := map[string]interface{}{}
+			hcl.DecodeObject(&kv, item)
+			for k, v := range kv {
+				rawConfig, err := NewRawConfig(map[string]interface{}{
+					"value": v,
+				})
+
+				if err != nil {
+					return nil, fmt.Errorf(
+						"error parsing local value %q at %s: %s",
+						k, item.Val.Pos(), err,
+					)
+				}
+
+				result = append(result, &Local{
+					Name:      k,
+					RawConfig: rawConfig,
+				})
+			}
+		}
+	}
+
+	return result, nil
+}
+
 // LoadOutputsHcl recurses into the given HCL object and turns
 // it into a mapping of outputs.
 func loadOutputsHcl(list *ast.ObjectList) ([]*Output, error) {

config/loader_test.go

@@ -180,17 +180,17 @@ func TestLoadFileBasic(t *testing.T) {
 	}
 
 	if c.Dir != "" {
-		t.Fatalf("bad: %#v", c.Dir)
+		t.Fatalf("wrong dir %#v; want %#v", c.Dir, "")
 	}
 
 	expectedTF := &Terraform{RequiredVersion: "foo"}
 	if !reflect.DeepEqual(c.Terraform, expectedTF) {
-		t.Fatalf("bad: %#v", c.Terraform)
+		t.Fatalf("wrong terraform block %#v; want %#v", c.Terraform, expectedTF)
 	}
 
 	expectedAtlas := &AtlasConfig{Name: "mitchellh/foo"}
 	if !reflect.DeepEqual(c.Atlas, expectedAtlas) {
-		t.Fatalf("bad: %#v", c.Atlas)
+		t.Fatalf("wrong atlas config %#v; want %#v", c.Atlas, expectedAtlas)
 	}
 
 	actual := variablesStr(c.Variables)
@@ -208,6 +208,10 @@ func TestLoadFileBasic(t *testing.T) {
 		t.Fatalf("bad:\n%s", actual)
 	}
 
+	if actual, want := localsStr(c.Locals), strings.TrimSpace(basicLocalsStr); actual != want {
+		t.Fatalf("wrong locals:\n%s\nwant:\n%s", actual, want)
+	}
+
 	actual = outputsStr(c.Outputs)
 	if actual != strings.TrimSpace(basicOutputsStr) {
 		t.Fatalf("bad:\n%s", actual)
@@ -288,6 +292,10 @@ func TestLoadFileBasic_json(t *testing.T) {
 		t.Fatalf("bad:\n%s", actual)
 	}
 
+	if actual, want := localsStr(c.Locals), strings.TrimSpace(basicLocalsStr); actual != want {
+		t.Fatalf("wrong locals:\n%s\nwant:\n%s", actual, want)
+	}
+
 	actual = outputsStr(c.Outputs)
 	if actual != strings.TrimSpace(basicOutputsStr) {
 		t.Fatalf("bad:\n%s", actual)
@@ -1055,6 +1063,18 @@ web_ip
     resource: aws_instance.web.private_ip
 `
 
+const basicLocalsStr = `
+literal
+literal_list
+literal_map
+security_group_ids
+  vars
+    resource: aws_security_group.firewall.*.id
+web_ip
+  vars
+    resource: aws_instance.web.private_ip
+`
+
 const basicProvidersStr = `
 aws
   access_key

config/test-fixtures/basic.tf

@@ -58,6 +58,17 @@ resource aws_instance "web" {
     }
 }
 
+locals {
+  security_group_ids = "${aws_security_group.firewall.*.id}"
+  web_ip = "${aws_instance.web.private_ip}"
+}
+
+locals {
+  literal = 2
+  literal_list = ["foo"]
+  literal_map = {"foo" = "bar"}
+}
+
 resource "aws_instance" "db" {
     security_groups = "${aws_security_group.firewall.*.id}"
     VPC = "foo"

config/test-fixtures/basic.tf.json

@@ -79,6 +79,14 @@
         }
     },
 
+    "locals": {
+        "security_group_ids": "${aws_security_group.firewall.*.id}",
+        "web_ip": "${aws_instance.web.private_ip}",
+        "literal": 2,
+        "literal_list": ["foo"],
+        "literal_map": {"foo": "bar"}
+    },
+
     "output": {
         "web_ip": {
             "value": "${aws_instance.web.private_ip}"