feat: support loading config values from environment (#55)

Author: twelvelabs

conf/loader.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"reflect"
 
+	"github.com/caarlos0/env/v8"  // spell: disable-line
 	"github.com/creasty/defaults" // spell: disable-line
 	yaml "gopkg.in/yaml.v3"
 
@@ -70,6 +71,10 @@ func (l *Loader[C]) load() (C, error) {
 			return l.Config, err
 		}
 	}
+	// Override values passed in via ENV var
+	if err := env.Parse(l.Config); err != nil {
+		return l.Config, err
+	}
 	// Validate
 	if err := validate.Struct(l.Config); err != nil {
 		return l.Config, err

conf/loader_test.go

@@ -27,12 +27,16 @@ func ExampleLoader() {
 }
 
 type MyConfig struct {
-	Name    string `default:"untitled"`
+	Name    string `default:"untitled" env:"CONFIG_NAME"`
 	Count   int    `default:"1" validate:"lt=100"`
 	Enabled bool
 	Tags    []string
 }
 
+type MyConfigWithError struct {
+	Name string `env:"CONFIG_NAME,unknown"` // unknown tag to trigger error
+}
+
 func FixturePath(names ...string) string {
 	name := "config.yaml"
 	if len(names) > 0 {
@@ -116,6 +120,24 @@ func TestLoader_LoadWhenYAMLError(t *testing.T) {
 	assert.ErrorContains(t, err, "boom")
 }
 
+func TestLoader_Load_WithEnv(t *testing.T) {
+	t.Setenv("CONFIG_NAME", "name from env var")
+
+	loader := NewLoader(&MyConfig{}, "")
+	config, err := loader.Load()
+	assert.NoError(t, err)
+	assert.Equal(t, "name from env var", config.Name)
+}
+
+func TestLoader_Load_WhenEnvError(t *testing.T) {
+	t.Setenv("CONFIG_NAME", "name from env var")
+
+	loader := NewLoader(&MyConfigWithError{}, "")
+	config, err := loader.Load()
+	assert.ErrorContains(t, err, `tag option "unknown" not supported`)
+	assert.Equal(t, "", config.Name)
+}
+
 func TestLoader_LoadWhenValidationError(t *testing.T) {
 	_, err := NewLoader(&MyConfig{}, FixturePath("invalid.yaml")).Load()
 	assert.ErrorContains(t, err, "Count must be less than 100")

go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/AlecAivazis/survey/v2 v2.3.6
 	github.com/Masterminds/sprig/v3 v3.2.3
 	github.com/briandowns/spinner v1.23.0
+	github.com/caarlos0/env/v8 v8.0.0
 	github.com/creasty/defaults v1.7.0
 	github.com/go-playground/locales v0.14.1
 	github.com/go-playground/universal-translator v0.18.1

go.sum

@@ -10,6 +10,8 @@ github.com/Netflix/go-expect v0.0.0-20220104043353-73e0943537d2 h1:+vx7roKuyA63n
 github.com/Netflix/go-expect v0.0.0-20220104043353-73e0943537d2/go.mod h1:HBCaDeC1lPdgDeDbhX8XFpy1jqjK0IBG8W5K+xYqA0w=
 github.com/briandowns/spinner v1.23.0 h1:alDF2guRWqa/FOZZYWjlMIx2L6H0wyewPxo/CH4Pt2A=
 github.com/briandowns/spinner v1.23.0/go.mod h1:rPG4gmXeN3wQV/TsAY4w8lPdIM6RX3yqeBQJSrbXjuE=
+github.com/caarlos0/env/v8 v8.0.0 h1:POhxHhSpuxrLMIdvTGARuZqR4Jjm8AYmoi/JKlcScs0=
+github.com/caarlos0/env/v8 v8.0.0/go.mod h1:7K4wMY9bH0esiXSSHlfHLX5xKGQMnkH5Fk4TDSSSzfo=
 github.com/creack/pty v1.1.17 h1:QeVUsEDNrLBW4tMgZHvxy18sKtr6VI492kBhUfhDJNI=
 github.com/creack/pty v1.1.17/go.mod h1:MOBLtS5ELjhRRrroQr9kyvTxUAFNvYEK993ew/Vr4O4=
 github.com/creasty/defaults v1.7.0 h1:eNdqZvc5B509z18lD8yc212CAqJNvfT1Jq6L8WowdBA=