[cmd/builder] Update builder flags precedence (open-telemetry#5726)

This PR updates the builder's config initialization so that flags always take precedence over configuration files or default values.

I opted not to use the collector's resolvers/converter approach as it felt overkill for this command. This approach takes advantage of the command's existing use of global vars, which isn't the best, but is at least consistent.

CHANGELOG.md

@@ -12,6 +12,8 @@
 
 ### 🧰 Bug fixes 🧰
 
+- Fix bug in ocb where flags did not take precedence. (#5726)
+
 ## v0.56.0 Beta
 
 ### 💡 Enhancements 💡

cmd/builder/go.mod

@@ -19,6 +19,7 @@ go 1.17
 require (
 	github.com/knadh/koanf v1.4.2
 	github.com/spf13/cobra v1.5.0
+	github.com/spf13/pflag v1.0.5
 	github.com/stretchr/testify v1.8.0
 	go.uber.org/zap v1.21.0
 )
@@ -31,7 +32,6 @@ require (
 	github.com/mitchellh/mapstructure v1.5.0 // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
-	github.com/spf13/pflag v1.0.5 // indirect
 	go.uber.org/atomic v1.7.0 // indirect
 	go.uber.org/multierr v1.8.0 // indirect
 	golang.org/x/sys v0.0.0-20211210111614-af8b64212486 // indirect

cmd/builder/internal/command.go

@@ -24,11 +24,23 @@ import (
 	"github.com/knadh/koanf/providers/file"
 	"github.com/knadh/koanf/providers/posflag"
 	"github.com/spf13/cobra"
+	flag "github.com/spf13/pflag"
 	"go.uber.org/zap"
 
 	"go.opentelemetry.io/collector/cmd/builder/internal/builder"
 )
 
+const (
+	skipCompilationFlag            = "skip-compilation"
+	distributionNameFlag           = "name"
+	distributionDescriptionFlag    = "description"
+	distributionVersionFlag        = "version"
+	distributionOtelColVersionFlag = "otelcol-version"
+	distributionOutputPathFlag     = "output-path"
+	distributionGoFlag             = "go"
+	distributionModuleFlag         = "module"
+)
+
 var (
 	cfgFile string
 	cfg     = builder.NewDefaultConfig()
@@ -48,7 +60,7 @@ build configuration given by the "--config" argument.
 `,
 		Args: cobra.NoArgs,
 		RunE: func(cmd *cobra.Command, args []string) error {
-			if err := initConfig(); err != nil {
+			if err := initConfig(cmd.Flags()); err != nil {
 				return err
 			}
 			if err := cfg.Validate(); err != nil {
@@ -73,14 +85,14 @@ build configuration given by the "--config" argument.
 	}
 
 	// the distribution parameters, which we accept as CLI flags as well
-	cmd.Flags().BoolVar(&cfg.SkipCompilation, "skip-compilation", false, "Whether builder should only generate go code with no compile of the collector (default false)")
-	cmd.Flags().StringVar(&cfg.Distribution.Name, "name", "otelcol-custom", "The executable name for the OpenTelemetry Collector distribution")
-	cmd.Flags().StringVar(&cfg.Distribution.Description, "description", "Custom OpenTelemetry Collector distribution", "A descriptive name for the OpenTelemetry Collector distribution")
-	cmd.Flags().StringVar(&cfg.Distribution.Version, "version", "1.0.0", "The version for the OpenTelemetry Collector distribution")
-	cmd.Flags().StringVar(&cfg.Distribution.OtelColVersion, "otelcol-version", cfg.Distribution.OtelColVersion, "Which version of OpenTelemetry Collector to use as base")
-	cmd.Flags().StringVar(&cfg.Distribution.OutputPath, "output-path", cfg.Distribution.OutputPath, "Where to write the resulting files")
-	cmd.Flags().StringVar(&cfg.Distribution.Go, "go", "", "The Go binary to use during the compilation phase. Default: go from the PATH")
-	cmd.Flags().StringVar(&cfg.Distribution.Module, "module", "go.opentelemetry.io/collector/cmd/builder", "The Go module for the new distribution")
+	cmd.Flags().BoolVar(&cfg.SkipCompilation, skipCompilationFlag, false, "Whether builder should only generate go code with no compile of the collector (default false)")
+	cmd.Flags().StringVar(&cfg.Distribution.Name, distributionNameFlag, "otelcol-custom", "The executable name for the OpenTelemetry Collector distribution")
+	cmd.Flags().StringVar(&cfg.Distribution.Description, distributionDescriptionFlag, "Custom OpenTelemetry Collector distribution", "A descriptive name for the OpenTelemetry Collector distribution")
+	cmd.Flags().StringVar(&cfg.Distribution.Version, distributionVersionFlag, "1.0.0", "The version for the OpenTelemetry Collector distribution")
+	cmd.Flags().StringVar(&cfg.Distribution.OtelColVersion, distributionOtelColVersionFlag, cfg.Distribution.OtelColVersion, "Which version of OpenTelemetry Collector to use as base")
+	cmd.Flags().StringVar(&cfg.Distribution.OutputPath, distributionOutputPathFlag, cfg.Distribution.OutputPath, "Where to write the resulting files")
+	cmd.Flags().StringVar(&cfg.Distribution.Go, distributionGoFlag, "", "The Go binary to use during the compilation phase. Default: go from the PATH")
+	cmd.Flags().StringVar(&cfg.Distribution.Module, distributionModuleFlag, "go.opentelemetry.io/collector/cmd/builder", "The Go module for the new distribution")
 
 	// version of this binary
 	cmd.AddCommand(versionCommand())
@@ -92,7 +104,7 @@ build configuration given by the "--config" argument.
 	return cmd, nil
 }
 
-func initConfig() error {
+func initConfig(flags *flag.FlagSet) error {
 	cfg.Logger.Info("OpenTelemetry Collector Builder",
 		zap.String("version", version), zap.String("date", date))
 
@@ -108,10 +120,47 @@ func initConfig() error {
 		return fmt.Errorf("failed to load environment variables: %w", err)
 	}
 
-	if err := k.UnmarshalWithConf("", &cfg, koanf.UnmarshalConf{Tag: "mapstructure"}); err != nil {
+	cfgFromFile := builder.Config{}
+	if err := k.UnmarshalWithConf("", &cfgFromFile, koanf.UnmarshalConf{Tag: "mapstructure"}); err != nil {
 		return fmt.Errorf("failed to unmarshal configuration: %w", err)
 	}
 
+	applyCfgFromFile(flags, cfgFromFile)
+
 	cfg.Logger.Info("Using config file", zap.String("path", cfgFile))
 	return nil
 }
+
+func applyCfgFromFile(flags *flag.FlagSet, cfgFromFile builder.Config) {
+	cfg.Exporters = cfgFromFile.Exporters
+	cfg.Extensions = cfgFromFile.Extensions
+	cfg.Receivers = cfgFromFile.Receivers
+	cfg.Processors = cfgFromFile.Processors
+	cfg.Replaces = cfgFromFile.Replaces
+	cfg.Excludes = cfgFromFile.Excludes
+
+	if !flags.Changed(skipCompilationFlag) && cfgFromFile.SkipCompilation {
+		cfg.SkipCompilation = cfgFromFile.SkipCompilation
+	}
+	if !flags.Changed(distributionNameFlag) && cfgFromFile.Distribution.Name != "" {
+		cfg.Distribution.Name = cfgFromFile.Distribution.Name
+	}
+	if !flags.Changed(distributionDescriptionFlag) && cfgFromFile.Distribution.Description != "" {
+		cfg.Distribution.Description = cfgFromFile.Distribution.Description
+	}
+	if !flags.Changed(distributionVersionFlag) && cfgFromFile.Distribution.Version != "" {
+		cfg.Distribution.Version = cfgFromFile.Distribution.Version
+	}
+	if !flags.Changed(distributionOtelColVersionFlag) && cfgFromFile.Distribution.OtelColVersion != "" {
+		cfg.Distribution.OtelColVersion = cfgFromFile.Distribution.OtelColVersion
+	}
+	if !flags.Changed(distributionOutputPathFlag) && cfgFromFile.Distribution.OutputPath != "" {
+		cfg.Distribution.OutputPath = cfgFromFile.Distribution.OutputPath
+	}
+	if !flags.Changed(distributionGoFlag) && cfgFromFile.Distribution.Go != "" {
+		cfg.Distribution.Go = cfgFromFile.Distribution.Go
+	}
+	if !flags.Changed(distributionModuleFlag) && cfgFromFile.Distribution.Module != "" {
+		cfg.Distribution.Module = cfgFromFile.Distribution.Module
+	}
+}