feat: gate weak deps feature behind --go-library-weak-deps flag

The weak dependency feature is now opt-in via CLI flag.
When not enabled, Go library dependencies behave as regular hard dependencies.

Co-authored-by: Ona <no-reply@ona.com>

Author: iQQBot

cmd/build.go

@@ -241,6 +241,7 @@ func addBuildFlags(cmd *cobra.Command) {
 	cmd.Flags().Bool("report-github", os.Getenv("GITHUB_OUTPUT") != "", "Report package build success/failure to GitHub Actions using the GITHUB_OUTPUT environment variable")
 	cmd.Flags().Bool("fixed-build-dir", true, "Use a fixed build directory for each package, instead of based on the package version, to better utilize caches based on absolute paths (defaults to true)")
 	cmd.Flags().Bool("docker-export-to-cache", false, "Export Docker images to cache instead of pushing directly (enables SLSA L3 compliance)")
+	cmd.Flags().Bool("go-library-weak-deps", false, "Treat Go library dependencies as weak dependencies (copy source instead of built artifacts)")
 }
 
 func getBuildOpts(cmd *cobra.Command) ([]leeway.BuildOption, cache.LocalCache) {
@@ -412,6 +413,11 @@ func getBuildOpts(cmd *cobra.Command) ([]leeway.BuildOption, cache.LocalCache) {
 		dockerExportSet = true
 	}
 
+	goLibraryWeakDeps, err := cmd.Flags().GetBool("go-library-weak-deps")
+	if err != nil {
+		log.Fatal(err)
+	}
+
 	return []leeway.BuildOption{
 		leeway.WithLocalCache(localCache),
 		leeway.WithRemoteCache(remoteCache),
@@ -430,6 +436,7 @@ func getBuildOpts(cmd *cobra.Command) ([]leeway.BuildOption, cache.LocalCache) {
 		leeway.WithInFlightChecksums(inFlightChecksums),
 		leeway.WithDockerExportToCache(dockerExportToCache, dockerExportSet),
 		leeway.WithDockerExportEnv(dockerExportEnvValue, dockerExportEnvSet),
+		leeway.WithGoLibraryWeakDeps(goLibraryWeakDeps),
 	}, localCache
 }
 

pkg/leeway/build.go

@@ -586,6 +586,11 @@ type buildOptions struct {
 	DockerExportEnvValue bool // Value from explicit user env var
 	DockerExportEnvSet   bool // Whether user explicitly set env var (before workspace)
 
+	// GoLibraryWeakDeps enables treating Go library dependencies as weak dependencies.
+	// When enabled, Go library deps copy source code instead of built artifacts,
+	// allowing parallel builds while still running tests.
+	GoLibraryWeakDeps bool
+
 	context *buildContext
 }
 
@@ -734,6 +739,16 @@ func WithDockerExportEnv(value, isSet bool) BuildOption {
 	}
 }
 
+// WithGoLibraryWeakDeps enables treating Go library dependencies as weak dependencies.
+// When enabled, Go library deps copy source code instead of built artifacts,
+// allowing parallel builds while still running tests.
+func WithGoLibraryWeakDeps(enabled bool) BuildOption {
+	return func(opts *buildOptions) error {
+		opts.GoLibraryWeakDeps = enabled
+		return nil
+	}
+}
+
 func withBuildContext(ctx *buildContext) BuildOption {
 	return func(opts *buildOptions) error {
 		opts.context = ctx
@@ -781,18 +796,22 @@ func Build(pkg *Package, opts ...BuildOption) (err error) {
 	requirements := pkg.GetTransitiveDependencies()
 	allpkg := append(requirements, pkg)
 
-	weakDeps := collectWeakDependencies(pkg)
-	for _, wd := range weakDeps {
-		// Only add if not already in allpkg (avoid duplicates)
-		found := false
-		for _, p := range allpkg {
-			if p.FullName() == wd.FullName() {
-				found = true
-				break
+	// Only collect weak deps if the feature is enabled
+	var weakDeps []*Package
+	if ctx.GoLibraryWeakDeps {
+		weakDeps = collectWeakDependencies(pkg)
+		for _, wd := range weakDeps {
+			// Only add if not already in allpkg (avoid duplicates)
+			found := false
+			for _, p := range allpkg {
+				if p.FullName() == wd.FullName() {
+					found = true
+					break
+				}
+			}
+			if !found {
+				allpkg = append(allpkg, wd)
 			}
-		}
-		if !found {
-			allpkg = append(allpkg, wd)
 		}
 	}
 
@@ -2293,7 +2312,12 @@ func (p *Package) buildGo(buildctx *buildContext, wd, result string) (res *packa
 	}
 
 	transdep := p.GetTransitiveDependencies()
-	weakdeps := p.GetTransitiveWeakDependencies()
+
+	// Only use weak deps if the feature is enabled via CLI flag
+	var weakdeps []*Package
+	if buildctx.GoLibraryWeakDeps {
+		weakdeps = p.GetTransitiveWeakDependencies()
+	}
 	needsDepsDir := len(transdep) > 0 || len(weakdeps) > 0
 
 	if needsDepsDir {