fix: track if there is no service config (#3281)

In our code we're assuming if there is no service config that we should
automatically derive it, this is incorrect, sometimes a service config
does not exist: example
[orgpolicy](https://github.com/googleapis/googleapis/tree/master/google/cloud/orgpolicy/v1).
We need to track when migrating from sidekick if the service config does
not exist, and if it doesn't we shouldn't try automatically derive.

Fix #3273

---------

Signed-off-by: ldetmer <[email protected]>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: ldetmer

devtools/cmd/migrate-sidekick/main.go

@@ -590,8 +590,15 @@ func buildConfig(libraries map[string]*config.Library, defaults *config.Config)
 	for _, lib := range libraries {
 		// Get the API path for this library
 		apiPath := ""
+		serviceConfigDoesNotExist := false
 		if len(lib.Channels) > 0 {
 			apiPath = lib.Channels[0].Path
+			for _, ch := range lib.Channels {
+				if ch.ServiceConfig == "" {
+					ch.ServiceConfigDoesNotExist = true
+					serviceConfigDoesNotExist = true
+				}
+			}
 		}
 
 		// Derive expected library name from API path
@@ -603,11 +610,8 @@ func buildConfig(libraries map[string]*config.Library, defaults *config.Config)
 				lib.Rust.GenerateSetterSamples != "" || lib.Rust.GenerateRpcSamples ||
 				len(lib.Rust.PackageDependencies) > 0 || len(lib.Rust.PaginationOverrides) > 0 ||
 				lib.Rust.NameOverrides != ""))
-		// Only include in libraries section if:
-		// 1. Name doesn't match expected naming convention (name override)
-		// 2. Library has extra configuration
-		// 3. Library spans multiple APIs
-		if !nameMatchesConvention || hasExtraConfig || len(lib.Channels) > 1 {
+		// Only include in libraries section if specific data needs to be retained
+		if !nameMatchesConvention || hasExtraConfig || len(lib.Channels) > 1 || serviceConfigDoesNotExist {
 			libCopy := *lib
 			libList = append(libList, &libCopy)
 		}

devtools/cmd/migrate-sidekick/main_test.go

@@ -561,6 +561,56 @@ func TestBuildConfig(t *testing.T) {
 				},
 			},
 		},
+		{
+			name:     "service does not exist",
+			defaults: &config.Config{},
+			libraries: map[string]*config.Library{
+				"google-cloud-security-publicca-v1": {
+					Name: "google-cloud-security-publicca-v1",
+					Channels: []*config.Channel{
+						{
+							Path: "google/cloud/security/publicca/v1",
+						},
+					},
+					Version:       "1.1.0",
+					CopyrightYear: "2025",
+					Rust: &config.RustCrate{
+						RustDefault: config.RustDefault{
+							DisabledRustdocWarnings: []string{"bare_urls", "broken_intra_doc_links", "redundant_explicit_links"},
+							GenerateSetterSamples:   "true",
+						},
+						PerServiceFeatures: true,
+						GenerateRpcSamples: true,
+						NameOverrides:      ".google.cloud.security/publicca.v1.Storage=StorageControl",
+					},
+				},
+			},
+			want: &config.Config{
+				Libraries: []*config.Library{
+					{
+						Name: "google-cloud-security-publicca-v1",
+						Channels: []*config.Channel{
+							{
+								ServiceConfigDoesNotExist: true,
+								Path:                      "google/cloud/security/publicca/v1",
+								ServiceConfig:             "",
+							},
+						},
+						Version:       "1.1.0",
+						CopyrightYear: "2025",
+						Rust: &config.RustCrate{
+							RustDefault: config.RustDefault{
+								DisabledRustdocWarnings: []string{"bare_urls", "broken_intra_doc_links", "redundant_explicit_links"},
+								GenerateSetterSamples:   "true",
+							},
+							PerServiceFeatures: true,
+							GenerateRpcSamples: true,
+							NameOverrides:      ".google.cloud.security/publicca.v1.Storage=StorageControl",
+						},
+					},
+				},
+			},
+		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			got := buildConfig(test.libraries, test.defaults)

internal/config/config.go

@@ -209,4 +209,7 @@ type Channel struct {
 
 	// ServiceConfig is the path to the service config file.
 	ServiceConfig string `yaml:"service_config,omitempty"`
+
+	// ServiceConfigDoesNotExist specifies if there is no service config for this channel.
+	ServiceConfigDoesNotExist bool `yaml:"service_config_does_not_exist,omitempty"`
 }

internal/librarian/generate.go

@@ -266,7 +266,7 @@ func prepareLibrary(language string, lib *config.Library, defaults *config.Defau
 			if ch.Path == "" {
 				ch.Path = deriveChannelPath(language, lib)
 			}
-			if ch.ServiceConfig == "" {
+			if ch.ServiceConfig == "" && !ch.ServiceConfigDoesNotExist {
 				ch.ServiceConfig = deriveServiceConfig(ch.Path)
 			}
 		}

internal/librarian/generate_test.go

@@ -279,6 +279,14 @@ func TestPrepareLibrary(t *testing.T) {
 			output:     "src/storage",
 			wantOutput: "src/storage",
 		},
+		{
+			name:              "rust lib without service config does not derive service config",
+			language:          "rust",
+			channels:          []*config.Channel{{ServiceConfigDoesNotExist: true}},
+			wantOutput:        "src/generated/cloud/test/v1",
+			wantChannelPath:   "google/cloud/test/v1",
+			wantServiceConfig: "",
+		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			lib := &config.Library{

internal/librarian/tidy.go

@@ -64,7 +64,7 @@ func RunTidy() error {
 			}
 		}
 		lib.Channels = slices.DeleteFunc(lib.Channels, func(ch *config.Channel) bool {
-			return ch.Path == "" && ch.ServiceConfig == ""
+			return ch.Path == "" && ch.ServiceConfig == "" && !ch.ServiceConfigDoesNotExist
 		})
 
 		tidyLanguageConfig(lib, cfg.Language)

internal/librarian/tidy_test.go

@@ -129,12 +129,13 @@ libraries:
 
 func TestTidy_DerivableFields(t *testing.T) {
 	for _, test := range []struct {
-		name          string
-		configContent string
-		wantPath      string
-		wantSvcCfg    string
-		wantNumLibs   int
-		wantNumChnls  int
+		name                 string
+		configContent        string
+		wantPath             string
+		wantSvcCfg           string
+		wantNumLibs          int
+		wantNumChnls         int
+		wantServiceConfigDne bool
 	}{
 		{
 			name: "derivable fields removed",
@@ -205,6 +206,20 @@ libraries:
 			wantNumLibs:  1,
 			wantNumChnls: 1,
 		},
+		{
+			name: "channel remains if service config does not exist",
+			configContent: `
+libraries:
+  - name: google-cloud-accessapproval-v1
+    channels:
+      - service_config_does_not_exist: true
+`,
+			wantPath:             "",
+			wantSvcCfg:           "",
+			wantNumLibs:          1,
+			wantNumChnls:         1,
+			wantServiceConfigDne: true,
+		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			tempDir := t.TempDir()
@@ -238,6 +253,9 @@ libraries:
 				if ch.ServiceConfig != test.wantSvcCfg {
 					t.Errorf("service_config should be %s, got %q", test.wantSvcCfg, ch.ServiceConfig)
 				}
+				if ch.ServiceConfigDoesNotExist != test.wantServiceConfigDne {
+					t.Errorf("service_config_does_not_exist should be %t, got %t", test.wantServiceConfigDne, ch.ServiceConfigDoesNotExist)
+				}
 			}
 		})
 	}