Enforce alphabetical ordering of packages in YAML config (#22)

1 files changed, 33 insertions, 4 deletions

diff --git a/config.go b/config.go
index 5071f37..735b147 100644
--- a/config.go
+++ b/config.go
@@ -1,7 +1,9 @@
 package main
 
 import (
+	"fmt"
 	"io/ioutil"
+	"sort"
 
 	"gopkg.in/yaml.v2"
 )
@@ -17,18 +19,45 @@ type Package struct {
 	Repo string `yaml:"repo"`
 }
 
+// ensureAlphabetical checks that the packages are listed alphabetically in the configuration.
+func ensureAlphabetical(data []byte) bool {
+	// A yaml.MapSlice perservers ordering of keys: https://godoc.org/gopkg.in/yaml.v2#MapSlice
+	var c struct {
+		Packages yaml.MapSlice `yaml:"packages"`
+	}
+
+	if err := yaml.Unmarshal(data, &c); err != nil {
+		return false
+	}
+
+	packageNames := make([]string, 0, len(c.Packages))
+	for _, v := range c.Packages {
+		name, ok := v.Key.(string)
+		if !ok {
+			return false
+		}
+		packageNames = append(packageNames, name)
+	}
+
+	return sort.StringsAreSorted(packageNames)
+}
+
 // Parse takes a path to a yaml file and produces a parsed Config
-func Parse(path string) (Config, error) {
+func Parse(path string) (*Config, error) {
 	var c Config
 
 	data, err := ioutil.ReadFile(path)
 	if err != nil {
-		return c, err
+		return nil, err
 	}
 
 	if err := yaml.Unmarshal(data, &c); err != nil {
-		return c, err
+		return nil, err
+	}
+
+	if !ensureAlphabetical(data) {
+		return nil, fmt.Errorf("packages in %s must be alphabetically ordered", path)
 	}
 
-	return c, err
+	return &c, err
 }