config: manually parse variable blocks for better validation

Fixes #7846

This changes from using the HCL decoder to manually decoding the
`variable` blocks within the configuration. This gives us a lot more
power to catch validation errors. This PR retains the same tests and
fixes one additional issue (covered by a test) in the case where a
variable has no named assigned.

config/loader_hcl.go

@@ -28,62 +28,21 @@ func (t *hclConfigurable) Config() (*Config, error) {
 		"variable": struct{}{},
 	}
 
-	type hclVariable struct {
-		Name         string `hcl:",key"`
-		Default      interface{}
-		Description  string
-		DeclaredType string   `hcl:"type"`
-		Fields       []string `hcl:",decodedFields"`
-	}
-
-	var rawConfig struct {
-		Variable []*hclVariable
-	}
-
 	// Top-level item should be the object list
 	list, ok := t.Root.Node.(*ast.ObjectList)
 	if !ok {
 		return nil, fmt.Errorf("error parsing: file doesn't contain a root object")
 	}
 
-	if err := hcl.DecodeObject(&rawConfig, list); err != nil {
-		return nil, err
-	}
-
-	// Start building up the actual configuration. We start with
-	// variables.
-	// TODO(mitchellh): Make function like loadVariablesHcl so that
-	// duplicates aren't overriden
+	// Start building up the actual configuration.
 	config := new(Config)
-	if len(rawConfig.Variable) > 0 {
-		config.Variables = make([]*Variable, 0, len(rawConfig.Variable))
-		for _, v := range rawConfig.Variable {
-			// Defaults turn into a slice of map[string]interface{} and
-			// we need to make sure to convert that down into the
-			// proper type for Config.
-			if ms, ok := v.Default.([]map[string]interface{}); ok {
-				def := make(map[string]interface{})
-				for _, m := range ms {
-					for k, v := range m {
-						def[k] = v
-					}
-				}
 
-				v.Default = def
-			}
-
-			newVar := &Variable{
-				Name:         v.Name,
-				DeclaredType: v.DeclaredType,
-				Default:      v.Default,
-				Description:  v.Description,
-			}
-
-			if err := newVar.ValidateTypeAndDefault(); err != nil {
-				return nil, err
-			}
-
-			config.Variables = append(config.Variables, newVar)
+	// Build the variables
+	if vars := list.Filter("variable"); len(vars.Items) > 0 {
+		var err error
+		config.Variables, err = loadVariablesHcl(vars)
+		if err != nil {
+			return nil, err
 		}
 	}
 
@@ -354,6 +313,84 @@ func loadOutputsHcl(list *ast.ObjectList) ([]*Output, error) {
 	return result, nil
 }
 
+// LoadVariablesHcl recurses into the given HCL object and turns
+// it into a list of variables.
+func loadVariablesHcl(list *ast.ObjectList) ([]*Variable, error) {
+	list = list.Children()
+	if len(list.Items) == 0 {
+		return nil, fmt.Errorf(
+			"'variable' must be followed by exactly one strings: a name")
+	}
+
+	// hclVariable is the structure each variable is decoded into
+	type hclVariable struct {
+		DeclaredType string `hcl:"type"`
+		Default      interface{}
+		Description  string
+		Fields       []string `hcl:",decodedFields"`
+	}
+
+	// Go through each object and turn it into an actual result.
+	result := make([]*Variable, 0, len(list.Items))
+	for _, item := range list.Items {
+		// Clean up items from JSON
+		unwrapHCLObjectKeysFromJSON(item, 1)
+
+		// Verify the keys
+		if len(item.Keys) != 1 {
+			return nil, fmt.Errorf(
+				"position %s: 'variable' must be followed by exactly one strings: a name",
+				item.Pos())
+		}
+
+		n := item.Keys[0].Token.Value().(string)
+
+		/*
+			// TODO: catch extra fields
+			// Decode into raw map[string]interface{} so we know ALL fields
+			var config map[string]interface{}
+			if err := hcl.DecodeObject(&config, item.Val); err != nil {
+				return nil, err
+			}
+		*/
+
+		// Decode into hclVariable to get typed values
+		var hclVar hclVariable
+		if err := hcl.DecodeObject(&hclVar, item.Val); err != nil {
+			return nil, err
+		}
+
+		// Defaults turn into a slice of map[string]interface{} and
+		// we need to make sure to convert that down into the
+		// proper type for Config.
+		if ms, ok := hclVar.Default.([]map[string]interface{}); ok {
+			def := make(map[string]interface{})
+			for _, m := range ms {
+				for k, v := range m {
+					def[k] = v
+				}
+			}
+
+			hclVar.Default = def
+		}
+
+		// Build the new variable and do some basic validation
+		newVar := &Variable{
+			Name:         n,
+			DeclaredType: hclVar.DeclaredType,
+			Default:      hclVar.Default,
+			Description:  hclVar.Description,
+		}
+		if err := newVar.ValidateTypeAndDefault(); err != nil {
+			return nil, err
+		}
+
+		result = append(result, newVar)
+	}
+
+	return result, nil
+}
+
 // LoadProvidersHcl recurses into the given HCL object and turns
 // it into a mapping of provider configs.
 func loadProvidersHcl(list *ast.ObjectList) ([]*ProviderConfig, error) {
@@ -557,36 +594,8 @@ func loadManagedResourcesHcl(list *ast.ObjectList) ([]*Resource, error) {
 				item.Pos())
 		}
 
-		// HCL special case: if we're parsing JSON then directly nested
-		// items will show up as additional "keys". We need to unwrap them
-		// since we expect only two keys. Example:
-		//
-		// { "foo": { "bar": { "baz": {} } } }
-		//
-		// Will show up with Keys being: []string{"foo", "bar", "baz"}
-		// when we really just want the first two. To fix this we unwrap
-		// them into the right value.
-		if len(item.Keys) > 2 && item.Keys[0].Token.JSON {
-			for len(item.Keys) > 2 {
-				// Pop off the last key
-				n := len(item.Keys)
-				key := item.Keys[n-1]
-				item.Keys[n-1] = nil
-				item.Keys = item.Keys[:n-1]
-
-				// Wrap our value in a list
-				item.Val = &ast.ObjectType{
-					List: &ast.ObjectList{
-						Items: []*ast.ObjectItem{
-							&ast.ObjectItem{
-								Keys: []*ast.ObjectKey{key},
-								Val:  item.Val,
-							},
-						},
-					},
-				}
-			}
-		}
+		// Fix up JSON input
+		unwrapHCLObjectKeysFromJSON(item, 2)
 
 		if len(item.Keys) != 2 {
 			return nil, fmt.Errorf(
@@ -864,3 +873,42 @@ func checkHCLKeys(node ast.Node, valid []string) error {
 
 	return result
 }
+
+// unwrapHCLObjectKeysFromJSON cleans up an edge case that can occur when
+// parsing JSON as input: if we're parsing JSON then directly nested
+// items will show up as additional "keys".
+//
+// For objects that expect a fixed number of keys, this breaks the
+// decoding process. This function unwraps the object into what it would've
+// looked like if it came directly from HCL by specifying the number of keys
+// you expect.
+//
+// Example:
+//
+// { "foo": { "baz": {} } }
+//
+// Will show up with Keys being: []string{"foo", "baz"}
+// when we really just want the first two. This function will fix this.
+func unwrapHCLObjectKeysFromJSON(item *ast.ObjectItem, depth int) {
+	if len(item.Keys) > depth && item.Keys[0].Token.JSON {
+		for len(item.Keys) > depth {
+			// Pop off the last key
+			n := len(item.Keys)
+			key := item.Keys[n-1]
+			item.Keys[n-1] = nil
+			item.Keys = item.Keys[:n-1]
+
+			// Wrap our value in a list
+			item.Val = &ast.ObjectType{
+				List: &ast.ObjectList{
+					Items: []*ast.ObjectItem{
+						&ast.ObjectItem{
+							Keys: []*ast.ObjectKey{key},
+							Val:  item.Val,
+						},
+					},
+				},
+			}
+		}
+	}
+}

config/loader_test.go

@@ -549,6 +549,18 @@ func TestLoadFile_badVariableTypes(t *testing.T) {
 	}
 }
 
+func TestLoadFile_variableNoName(t *testing.T) {
+	_, err := LoadFile(filepath.Join(fixtureDir, "variable-no-name.tf"))
+	if err == nil {
+		t.Fatalf("bad: expected error")
+	}
+
+	errorStr := err.Error()
+	if !strings.Contains(errorStr, "'variable' must be followed") {
+		t.Fatalf("bad: expected error has wrong text: %s", errorStr)
+	}
+}
+
 func TestLoadFile_provisioners(t *testing.T) {
 	c, err := LoadFile(filepath.Join(fixtureDir, "provisioners.tf"))
 	if err != nil {

config/test-fixtures/variable-no-name.tf

@@ -0,0 +1,5 @@
+variable {
+  name    = "test"
+  default = "test_value"
+  type    = "string"
+}