[builder] Support for --skip-new-go-module

cmd/builder/README.md

@@ -152,6 +152,26 @@ ocb --skip-generate --skip-get-modules --config=config.yaml
 ```
 to only execute the compilation step.
 
+### Avoiding the use of a new go.mod file
+
+There is an additional option that controls one aspect of the build
+process, which specifically allows skipping the use of a new `go.mod`
+file.  When the `--skip-new-go-module` command-line flag is supplied,
+the build process issues a `go get` command for each component,
+relying on the Go toolchain to update the enclosing Go module
+appropriately.
+
+This command will avoid downgrading a dependency in the enclosing
+module, according to
+[`semver.Compare()`](https://pkg.go.dev/golang.org/x/mod/semver#Compare),
+and will instead issue a log indicating that the component was not
+upgraded.
+
+This mode cannot be used in conjunction with several features that
+control the generated `go.mod` file, including `replaces`, `excludes`,
+and the component `path` override.  For each of these features, users
+are expected to modify the enclosing `go.mod` directly.
+
 ### Strict versioning checks
 
 The builder checks the relevant `go.mod`

cmd/builder/internal/builder/config.go

@@ -19,8 +19,12 @@ import (
 
 const defaultOtelColVersion = "0.100.0"
 
-// ErrInvalidGoMod indicates an invalid gomod
-var ErrInvalidGoMod = errors.New("invalid gomod specification for module")
+var (
+	// ErrInvalidGoMod indicates an invalid gomod
+	ErrInvalidGoMod = errors.New("invalid gomod specification for module")
+	// ErrIncompatibleConfigurationValues indicates that there is configuration that cannot be combined
+	ErrIncompatibleConfigurationValues = errors.New("cannot combine configuration values")
+)
 
 // Config holds the builder's configuration
 type Config struct {
@@ -29,6 +33,7 @@ type Config struct {
 	SkipGenerate         bool   `mapstructure:"-"`
 	SkipCompilation      bool   `mapstructure:"-"`
 	SkipGetModules       bool   `mapstructure:"-"`
+	SkipNewGoModule      bool   `mapstructure:"-"`
 	SkipStrictVersioning bool   `mapstructure:"-"`
 	LDFlags              string `mapstructure:"-"`
 	Verbose              bool   `mapstructure:"-"`
@@ -106,14 +111,15 @@ func NewDefaultConfig() Config {
 func (c *Config) Validate() error {
 	var providersError error
 	if c.Providers != nil {
-		providersError = validateModules(*c.Providers)
+		providersError = c.validateModules(*c.Providers)
 	}
 	return multierr.Combine(
-		validateModules(c.Extensions),
-		validateModules(c.Receivers),
-		validateModules(c.Exporters),
-		validateModules(c.Processors),
-		validateModules(c.Connectors),
+		c.validateModules(c.Extensions),
+		c.validateModules(c.Receivers),
+		c.validateModules(c.Exporters),
+		c.validateModules(c.Processors),
+		c.validateModules(c.Connectors),
+		c.validateFlags(),
 		providersError,
 	)
 }
@@ -226,11 +232,21 @@ func (c *Config) ParseModules() error {
 	return nil
 }
 
-func validateModules(mods []Module) error {
+func (c *Config) validateFlags() error {
+	if c.SkipNewGoModule && (len(c.Replaces) != 0 || len(c.Excludes) != 0) {
+		return fmt.Errorf("%w excludes or replaces with --skip-new-go-module; please modify the enclosing go.mod file directly", ErrIncompatibleConfigurationValues)
+	}
+	return nil
+}
+
+func (c *Config) validateModules(mods []Module) error {
 	for _, mod := range mods {
 		if mod.GoMod == "" {
 			return fmt.Errorf("module %q: %w", mod.GoMod, ErrInvalidGoMod)
 		}
+		if mod.Path != "" && c.SkipNewGoModule {
+			return fmt.Errorf("%w cannot modify mod.path \"%v\" combined with --skip-new-go-module; please modify the enclosing go.mod file directly", ErrIncompatibleConfigurationValues, mod.Path)
+		}
 	}
 	return nil
 }

cmd/builder/internal/builder/config_test.go

@@ -4,7 +4,6 @@
 package builder
 
 import (
-	"errors"
 	"os"
 	"strings"
 	"testing"
@@ -122,10 +121,37 @@ func TestInvalidModule(t *testing.T) {
 			},
 			err: ErrInvalidGoMod,
 		},
+		{
+			cfg: Config{
+				Logger:          zap.NewNop(),
+				SkipNewGoModule: true,
+				Extensions: []Module{{
+					GoMod: "some-module",
+					Path:  "invalid",
+				}},
+			},
+			err: ErrIncompatibleConfigurationValues,
+		},
+		{
+			cfg: Config{
+				Logger:          zap.NewNop(),
+				SkipNewGoModule: true,
+				Replaces:        []string{"", ""},
+			},
+			err: ErrIncompatibleConfigurationValues,
+		},
+		{
+			cfg: Config{
+				Logger:          zap.NewNop(),
+				SkipNewGoModule: true,
+				Excludes:        []string{"", ""},
+			},
+			err: ErrIncompatibleConfigurationValues,
+		},
 	}
 
 	for _, test := range configurations {
-		assert.True(t, errors.Is(test.cfg.Validate(), test.err))
+		assert.ErrorIs(t, test.cfg.Validate(), test.err)
 	}
 }
 

cmd/builder/internal/builder/main.go

@@ -85,18 +85,30 @@ func Generate(cfg Config) error {
 		return fmt.Errorf("failed to create output path: %w", err)
 	}
 
-	for _, tmpl := range []*template.Template{
+	allTemplates := []*template.Template{
 		mainTemplate,
 		mainOthersTemplate,
 		mainWindowsTemplate,
 		componentsTemplate,
-		goModTemplate,
-	} {
+	}
+
+	// Add the go.mod template unless that file is skipped.
+	if !cfg.SkipNewGoModule {
+		allTemplates = append(allTemplates, goModTemplate)
+	}
+
+	for _, tmpl := range allTemplates {
 		if err := processAndWrite(cfg, tmpl, tmpl.Name(), cfg); err != nil {
 			return fmt.Errorf("failed to generate source file %q: %w", tmpl.Name(), err)
 		}
 	}
 
+	// when not creating a new go.mod file, update modules one-by-one in the
+	// enclosing go module.
+	if err := cfg.updateModules(); err != nil {
+		return err
+	}
+
 	cfg.Logger.Info("Sources created", zap.String("path", cfg.Distribution.OutputPath))
 	return nil
 }
@@ -230,6 +242,64 @@ func (c *Config) allComponents() []Module {
 						*c.Providers...)...)...)...)...)
 }
 
+func (c *Config) updateModules() error {
+	if !c.SkipNewGoModule {
+		return nil
+	}
+
+	// Build the main service dependency
+	coremod, corever := c.coreModuleAndVersion()
+	corespec := coremod + " " + corever
+
+	if err := c.updateGoModule(corespec); err != nil {
+		return err
+	}
+
+	for _, comp := range c.allComponents() {
+		if err := c.updateGoModule(comp.GoMod); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (c *Config) updateGoModule(modspec string) error {
+	// Re-parse the go.mod file on each iteration, since it can
+	// change each time.
+	modulePath, dependencyVersions, err := c.readGoModFile()
+	if err != nil {
+		return err
+	}
+
+	mod, ver, _ := strings.Cut(modspec, " ")
+	if mod == modulePath {
+		// this component is part of the same module, nothing to update.
+		return nil
+	}
+
+	// check for exact match
+	hasVer, ok := dependencyVersions[mod]
+	if ok && hasVer == ver {
+		c.Logger.Info("Component version match", zap.String("module", mod), zap.String("version", ver))
+		return nil
+	}
+
+	scomp := semver.Compare(hasVer, ver)
+	if scomp > 0 {
+		// version in enclosing module is newer, do not change
+		c.Logger.Info("Not upgrading component, enclosing module is newer.", zap.String("module", mod), zap.String("existing", hasVer), zap.String("config_version", ver))
+		return nil
+	}
+
+	// upgrading or changing version
+	updatespec := mod + "@" + ver
+
+	if _, err := runGoCommand(*c, "get", updatespec); err != nil {
+		return err
+	}
+	return nil
+}
+
 func (c *Config) readGoModFile() (string, map[string]string, error) {
 	var modPath string
 	stdout, err := runGoCommand(*c, "mod", "edit", "-print")

cmd/builder/internal/command.go

@@ -23,6 +23,7 @@ const (
 	skipGenerateFlag               = "skip-generate"
 	skipCompilationFlag            = "skip-compilation"
 	skipGetModulesFlag             = "skip-get-modules"
+	skipNewGoModuleFlag            = "skip-new-go-module"
 	skipStrictVersioningFlag       = "skip-strict-versioning"
 	ldflagsFlag                    = "ldflags"
 	distributionNameFlag           = "name"
@@ -84,6 +85,7 @@ configuration is provided, ocb will generate a default Collector.
 	cmd.Flags().BoolVar(&cfg.SkipGenerate, skipGenerateFlag, false, "Whether builder should skip generating go code (default false)")
 	cmd.Flags().BoolVar(&cfg.SkipCompilation, skipCompilationFlag, false, "Whether builder should only generate go code with no compile of the collector (default false)")
 	cmd.Flags().BoolVar(&cfg.SkipGetModules, skipGetModulesFlag, false, "Whether builder should skip updating go.mod and retrieve Go module list (default false)")
+	cmd.Flags().BoolVar(&cfg.SkipNewGoModule, skipNewGoModuleFlag, false, "Whether builder should skip generating a new go.mod file, use enclosing Go module instead (default false)")
 	cmd.Flags().BoolVar(&cfg.SkipStrictVersioning, skipStrictVersioningFlag, false, "Whether builder should skip strictly checking the calculated versions following dependency resolution")
 	cmd.Flags().BoolVar(&cfg.Verbose, verboseFlag, false, "Whether builder should print verbose output (default false)")
 	cmd.Flags().StringVar(&cfg.LDFlags, ldflagsFlag, "", `ldflags to include in the "go build" command`)
@@ -183,6 +185,9 @@ func applyCfgFromFile(flags *flag.FlagSet, cfgFromFile builder.Config) {
 	if !flags.Changed(skipGetModulesFlag) && cfgFromFile.SkipGetModules {
 		cfg.SkipGetModules = cfgFromFile.SkipGetModules
 	}
+	if !flags.Changed(skipNewGoModuleFlag) && cfgFromFile.SkipNewGoModule {
+		cfg.SkipNewGoModule = cfgFromFile.SkipNewGoModule
+	}
 	if !flags.Changed(skipStrictVersioningFlag) && cfgFromFile.SkipStrictVersioning {
 		cfg.SkipStrictVersioning = cfgFromFile.SkipStrictVersioning
 	}