Find and use Gazelle's repo config in bb fix

cli/fix/fix.go

@@ -1,6 +1,7 @@
 package fix
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -72,7 +73,11 @@ func runGazelle(repoRoot, baseFile string) error {
 
 	os.Args = []string{"gazelle", "update"}
 	if baseFile == workspace.ModuleFileName {
-		os.Args = append(os.Args, "-bzlmod", "-repo_root="+repoRoot)
+		repoConfig, err := findRepoConfig(repoRoot)
+		if err != nil {
+			return fmt.Errorf("failed to find repo config: %w", err)
+		}
+		os.Args = append(os.Args, "-bzlmod", "-repo_root="+repoRoot, "-repo_config="+repoConfig)
 	} else {
 		os.Args = append(os.Args, "-repo_root="+repoRoot, "-go_prefix=")
 	}
@@ -85,6 +90,47 @@ func runGazelle(repoRoot, baseFile string) error {
 	return nil
 }
 
+// Finds the "repo config" file generated by gazelle's go_deps module extension
+// in its external repository. This file contains the mappings from Go module
+// paths to Bazel repository names and is required for correct gazelle behavior
+// with Bzlmod enabled.
+func findRepoConfig(repoRoot string) (string, error) {
+	// For the sake of performance and not interfering with the user's build,
+	// find the repo config file without invoking bazel. This assumes that
+	// the user has not disabled convenience symlinks.
+	// TODO: This may operate on stale information, consider forcing the
+	// go_deps extension to reevaluate before reading the config file.
+	bazelOutSymlink := filepath.Join(repoRoot, "bazel-out")
+	bazelOut, err := os.Readlink(bazelOutSymlink)
+	if errors.Is(err, os.ErrNotExist) {
+		return "", errors.New("failed to find bazel-out symlink, please run a build first")
+	} else if err != nil {
+		return "", fmt.Errorf("failed to read bazel-out symlink: %w", err)
+	}
+	// bazel-out has a path of the form <output_base>/execroot/_main/bazel-out.
+	outputBase := filepath.Dir(filepath.Dir(filepath.Dir(bazelOut)))
+	externalBase := filepath.Join(outputBase, "external")
+	// The separator in canonical repo names can be + or ~, depending on the
+	// Bazel version (>= 8 uses +, < 8 may use either depend on an incompatible
+	// flag).
+	gazelleConfigRepoGlob := filepath.Join(externalBase, "gazelle[~+][~+]go_deps[~+]bazel_gazelle_go_repository_config")
+	matches, err := filepath.Glob(gazelleConfigRepoGlob)
+	if err != nil {
+		return "", fmt.Errorf("failed to find repo config file: %w", err)
+	}
+	if len(matches) == 0 {
+		return "", errors.New("failed to find repo config file, please run a build first")
+	}
+	if len(matches) > 2 {
+		return "", fmt.Errorf("found unexpected number of repo config files: %s", strings.Join(matches, ", "))
+	}
+	// If the external directory hasn't been cleaned up since updating to
+	// Bazel 8, it may contain the repo directory both with ~ and + separators.
+	// The + separator is the more recent one in that case (assuming that users
+	// didn't switch back to Bazel 7) and sorts first.
+	return filepath.Join(matches[0], "WORKSPACE"), nil
+}
+
 func walk(moduleOrWorkspaceFile string) error {
 	languages := getLanguages()
 	foundLanguages := map[language.Language]bool{}

cli/workspace/workspace.go

@@ -15,8 +15,7 @@ const (
 	WorkspaceFileName    = "WORKSPACE"
 	WorkspaceAltFileName = "WORKSPACE.bazel"
 
-	ModuleFileName          = "MODULE.bazel"
-	ModuleWorkspaceFileName = "WORKSPACE.bzlmod"
+	ModuleFileName = "MODULE.bazel"
 )
 
 var (
@@ -25,7 +24,7 @@ var (
 	pathErr  error
 	basename string
 
-	WorkspaceIndicatorFiles = []string{WorkspaceFileName, WorkspaceAltFileName, ModuleFileName}
+	WorkspaceIndicatorFiles = []string{ModuleFileName, WorkspaceFileName, WorkspaceAltFileName}
 )
 
 // Path returns the current Bazel workspace path by traversing upwards until