make config file optional

Makefile

@@ -1,5 +1,5 @@
 example:
-	go run . example/genql.yaml
+	go generate ./...
 	go run ./example/cmd/example/main.go csilvers
 
 .PHONY: example

README.md

@@ -43,6 +43,8 @@ func getViewer(ctx context.Context, client *graphql.Client) (*getViewerResponse,
 graphqlClient := graphql.NewClient("https://example.com/graphql", http.DefaultClient)
 viewerResp, _ := getViewer(context.Background(), graphqlClient)
 fmt.Println("you are", *viewerResp.Viewer.MyName)
+
+//go:generate go run github.com/Khan/genql
 ```
 
 For a complete working example, see `example/`.
@@ -64,6 +66,7 @@ Config options:
 - file locations (queries, generated, schema (or get via HTTP))
 - use ctx or not, including complexities of how Khan uses context
 - HTTP calling convention (is there enough variation to matter?)
+- proper config/arguments setup (e.g. with [viper](https://github.com/spf13/viper)
 
 Other:
 - error-checking/validation/etc. everywhere

generate/config.go

@@ -56,18 +56,22 @@ func (c *Config) ValidateAndFillDefaults() error {
 }
 
 func ReadAndValidateConfig(filename string) (*Config, error) {
-	text, err := ioutil.ReadFile(filename)
-	if err != nil {
-		return nil, fmt.Errorf("unreadable config file %v: %v", filename, err)
-	}
-
 	var config Config
-	err = yaml.Unmarshal(text, &config)
-	if err != nil {
-		return nil, fmt.Errorf("invalid config file %v: %v", filename, err)
+	if filename == "" {
+		config = *defaultConfig
+	} else {
+		text, err := ioutil.ReadFile(filename)
+		if err != nil {
+			return nil, fmt.Errorf("unreadable config file %v: %v", filename, err)
+		}
+
+		err = yaml.Unmarshal(text, &config)
+		if err != nil {
+			return nil, fmt.Errorf("invalid config file %v: %v", filename, err)
+		}
 	}
 
-	err = config.ValidateAndFillDefaults()
+	err := config.ValidateAndFillDefaults()
 	if err != nil {
 		return nil, fmt.Errorf("invalid config file %v: %v", filename, err)
 	}

generate/main.go

@@ -35,11 +35,12 @@ func Main() {
 		}
 	}()
 
-	if len(os.Args) != 2 {
-		// TODO: omit config to get it from genql.yaml, or to use the defaults.
-		err = fmt.Errorf("usage: %s genql.yaml", os.Args[0])
-		return
+	switch len(os.Args) {
+	case 2:
+		err = readConfigGenerateAndWrite(os.Args[1])
+	case 1:
+		err = readConfigGenerateAndWrite("")
+	default:
+		err = fmt.Errorf("usage: %s [config]", os.Args[0])
 	}
-
-	err = readConfigGenerateAndWrite(os.Args[1])
 }