fix(internal/librarian/rust): update top-level Cargo.toml after version bump (#3995)

In `librarian bump`, if a library version bumps, also update the top
level Cargo.toml for that entry. lock file upgrade is already done at
the end of bump
[here](https://github.com/googleapis/librarian/blob/43b900a12d48f699ffee781990826c93087b8f6f/internal/librarian/bump.go#L201).

Included small refactor to use semver package validated versions.

Manual tested with google-cloud-rust, with a manual fake change in auth.

Fix #3720

Author: zhumin8

internal/librarian/rust/bump.go

@@ -23,6 +23,7 @@ import (
 	"path/filepath"
 
 	"github.com/googleapis/librarian/internal/config"
+	"github.com/googleapis/librarian/internal/semver"
 )
 
 var (
@@ -46,9 +47,14 @@ func Bump(ctx context.Context, library *config.Library, output, version, gitExe,
 	return writeVersion(library, output, version)
 }
 
-func writeVersion(library *config.Library, output, version string) error {
+func writeVersion(library *config.Library, output, versionString string) error {
+	// validate version before writing to Cargo.toml
+	version, err := semver.Parse(versionString)
+	if err != nil {
+		return err
+	}
 	cargoFile := filepath.Join(output, "Cargo.toml")
-	_, err := os.Stat(cargoFile)
+	_, err = os.Stat(cargoFile)
 	switch {
 	case err != nil && !os.IsNotExist(err):
 		return err
@@ -57,7 +63,7 @@ func writeVersion(library *config.Library, output, version string) error {
 name                   = "%s"
 version                = "%s"
 edition                = "2021"
-`, library.Name, version)
+`, library.Name, version.String())
 		if err := os.WriteFile(cargoFile, []byte(cargo), 0644); err != nil {
 			return err
 		}
@@ -66,6 +72,11 @@ edition                = "2021"
 			return err
 		}
 	}
-	library.Version = version
+
+	// Update the workspace manifest if it exists.
+	if err := updateWorkspaceVersion("Cargo.toml", library.Name, version); err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	library.Version = version.String()
 	return nil
 }

internal/librarian/rust/bump_test.go

@@ -175,3 +175,94 @@ func TestBumpLibraryNoVersion(t *testing.T) {
 		})
 	}
 }
+
+func TestBumpUpdatesWorkspaceDependency(t *testing.T) {
+	testhelper.RequireCommand(t, "cargo")
+	testhelper.RequireCommand(t, "taplo")
+	for _, test := range []struct {
+		name       string
+		rootCargo  string
+		libName    string
+		oldVersion string
+		newVersion string
+		want       string
+	}{
+		{
+			name: "single line table",
+			rootCargo: `[workspace.dependencies]
+google-cloud-storage = { version = "0.1.0", path = "storage" }
+google-cloud-auth        = { default-features = false, version = "1.5", path = "src/auth" }
+`,
+			libName:    "google-cloud-storage",
+			oldVersion: "0.1.0",
+			newVersion: "0.2.0",
+			want:       `google-cloud-storage = { version = "0.2.0", path = "storage" }`,
+		},
+		{
+			name: "multiple spaces",
+			rootCargo: `[workspace.dependencies]
+google-cloud-storage    = { version = "0.1.0", path = "storage" }
+`,
+			libName:    "google-cloud-storage",
+			oldVersion: "0.1.0",
+			newVersion: "0.2.0",
+			want:       `google-cloud-storage    = { version = "0.2.0", path = "storage" }`,
+		},
+		{
+			name: "no spaces around equals",
+			rootCargo: `[workspace.dependencies]
+google-cloud-storage={version="0.1.0",path="storage"}
+`,
+			libName:    "google-cloud-storage",
+			oldVersion: "0.1.0",
+			newVersion: "0.2.0",
+			want:       `google-cloud-storage={version = "0.2.0",path="storage"}`,
+		},
+		{
+			name: "multiple occurrences",
+			rootCargo: `[workspace.dependencies]
+google-cloud-storage = { version = "0.1.0", path = "storage" }
+[dependencies]
+google-cloud-storage = { version = "0.1.0", path = "storage" }
+`,
+			libName:    "google-cloud-storage",
+			oldVersion: "0.1.0",
+			newVersion: "0.2.0",
+			want:       `version = "0.2.0"`, // Both lines should contain this
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			tmpDir := t.TempDir()
+			t.Chdir(tmpDir)
+
+			libDir := "storage"
+			if err := os.WriteFile("Cargo.toml", []byte(test.rootCargo), 0644); err != nil {
+				t.Fatal(err)
+			}
+			createCrate(t, libDir, test.libName, test.oldVersion)
+			lib := &config.Library{
+				Name:    test.libName,
+				Version: test.oldVersion,
+				Output:  libDir,
+			}
+
+			if err := writeVersion(lib, libDir, test.newVersion); err != nil {
+				t.Fatal(err)
+			}
+
+			checkCargoVersion(t, filepath.Join(libDir, "Cargo.toml"), test.newVersion)
+			rootContents, err := os.ReadFile("Cargo.toml")
+			if err != nil {
+				t.Fatal(err)
+			}
+			got := string(rootContents)
+			if test.name == "multiple occurrences" {
+				if strings.Count(got, test.want) != 2 {
+					t.Errorf("expected 2 occurrences of %q, got %d:\n%s", test.want, strings.Count(got, test.want), got)
+				}
+			} else if !strings.Contains(got, test.want) {
+				t.Errorf("root Cargo.toml was not updated:\nwant: %q\ngot:\n%s", test.want, got)
+			}
+		})
+	}
+}

internal/librarian/rust/update_manifest.go

@@ -18,10 +18,12 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"regexp"
 	"slices"
 	"strings"
 
 	"github.com/googleapis/librarian/internal/command"
+	"github.com/googleapis/librarian/internal/semver"
 )
 
 // CrateInfo contains the package information.
@@ -40,7 +42,7 @@ type Cargo struct {
 // line-based approach to preserve comments and formatting, which is important
 // because some Cargo.toml files are hand-crafted and contain comments that
 // must be preserved.
-func updateCargoVersion(path, newVersion string) error {
+func updateCargoVersion(path string, newVersion semver.Version) error {
 	contents, err := os.ReadFile(path)
 	if err != nil {
 		return err
@@ -53,7 +55,36 @@ func updateCargoVersion(path, newVersion string) error {
 	}
 	// The number of spaces may seem weird. They match the number of spaces in
 	// the mustache template.
-	lines[idx] = fmt.Sprintf(`version                = "%s"`, newVersion)
+	lines[idx] = fmt.Sprintf(`version                = "%s"`, newVersion.String())
+	return os.WriteFile(path, []byte(strings.Join(lines, "\n")), 0644)
+}
+
+var versionRegex = regexp.MustCompile(`version\s*=\s*"[^"]*"`)
+
+// updateWorkspaceVersion updates the version of a crate in a workspace Cargo.toml.
+// It searches for a line that starts with the crate name followed by "=" and
+// contains a "version =" field.
+func updateWorkspaceVersion(path, crateName string, newVersion semver.Version) error {
+	contents, err := os.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	lines := strings.Split(string(contents), "\n")
+	updated := false
+	for i, line := range lines {
+		trimmed := strings.TrimSpace(line)
+		if !strings.HasPrefix(trimmed, crateName) {
+			continue
+		}
+		after := strings.TrimSpace(trimmed[len(crateName):])
+		if strings.HasPrefix(after, "=") && versionRegex.MatchString(line) {
+			lines[i] = versionRegex.ReplaceAllString(line, fmt.Sprintf(`version = "%s"`, newVersion.String()))
+			updated = true
+		}
+	}
+	if !updated {
+		return nil
+	}
 	return os.WriteFile(path, []byte(strings.Join(lines, "\n")), 0644)
 }