refactor(internal/sidekick): migrate Discovery to api (#4111)

Migrate Discovery from internal/sidekick/config to
internal/sidekick/api. This centralizes model overrides and removes the
config dependency from the parser and language generators.

Fixes #4041

Author: jameslynnwu

internal/librarian/rust/codec.go

@@ -21,7 +21,6 @@ import (
 	"github.com/googleapis/librarian/internal/config"
 	"github.com/googleapis/librarian/internal/serviceconfig"
 	"github.com/googleapis/librarian/internal/sidekick/api"
-	sidekickconfig "github.com/googleapis/librarian/internal/sidekick/config"
 	"github.com/googleapis/librarian/internal/sidekick/parser"
 	"github.com/googleapis/librarian/internal/sidekick/source"
 )
@@ -89,14 +88,14 @@ func libraryToModelConfig(library *config.Library, ch *config.API, sources *sour
 			}
 		}
 		if library.Rust.Discovery != nil {
-			pollers := make([]*sidekickconfig.Poller, len(library.Rust.Discovery.Pollers))
+			pollers := make([]*api.Poller, len(library.Rust.Discovery.Pollers))
 			for i, poller := range library.Rust.Discovery.Pollers {
-				pollers[i] = &sidekickconfig.Poller{
+				pollers[i] = &api.Poller{
 					Prefix:   poller.Prefix,
 					MethodID: poller.MethodID,
 				}
 			}
-			modelCfg.Discovery = &sidekickconfig.Discovery{
+			modelCfg.Discovery = &api.Discovery{
 				OperationID: library.Rust.Discovery.OperationID,
 				Pollers:     pollers,
 			}

internal/librarian/rust/codec_test.go

@@ -21,7 +21,6 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"github.com/googleapis/librarian/internal/config"
 	"github.com/googleapis/librarian/internal/sidekick/api"
-	sidekickconfig "github.com/googleapis/librarian/internal/sidekick/config"
 	"github.com/googleapis/librarian/internal/sidekick/parser"
 	"github.com/googleapis/librarian/internal/sidekick/source"
 )
@@ -509,9 +508,9 @@ func TestLibraryToModelConfig(t *testing.T) {
 				Override: api.ModelOverride{
 					Title: "Google Compute Engine API",
 				},
-				Discovery: &sidekickconfig.Discovery{
+				Discovery: &api.Discovery{
 					OperationID: ".google.cloud.compute.v1.Operation",
-					Pollers: []*sidekickconfig.Poller{
+					Pollers: []*api.Poller{
 						{
 							Prefix:   "compute/v1/projects/{project}/zones/{zone}",
 							MethodID: ".google.cloud.compute.v1.zoneOperations.get",

internal/sidekick/config/discovery.go internal/sidekick/api/discovery.gointernal/sidekick/config/discovery.go renamed to internal/sidekick/api/discovery.go

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package config
+package api
 
 import (
 	"strings"
@@ -25,7 +25,7 @@ type Discovery struct {
 	// The ID of the LRO operation type.
 	//
 	// For example: ".google.cloud.compute.v1.Operation".
-	OperationID string `toml:"operation-id"`
+	OperationID string
 
 	// Possible prefixes to match the LRO polling RPCs.
 	//
@@ -45,7 +45,7 @@ type Poller struct {
 	Prefix string
 
 	// The corresponding method ID.
-	MethodID string `toml:"method-id"`
+	MethodID string
 }
 
 // LroServices returns the set of Discovery LRO services.

internal/sidekick/api/discovery_test.go

@@ -0,0 +1,71 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package api
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestLroServices(t *testing.T) {
+	d := &Discovery{
+		Pollers: []*Poller{
+			{Prefix: "p1", MethodID: "Service1.Method1"},
+			{Prefix: "p2", MethodID: "Service1.Method2"},
+			{Prefix: "p3", MethodID: "Service2.Method3"},
+		},
+	}
+	want := map[string]bool{
+		"Service1": true,
+		"Service2": true,
+	}
+	got := d.LroServices()
+	if diff := cmp.Diff(want, got); diff != "" {
+		t.Errorf("LroServices() mismatch (-want +got):\n%s", diff)
+	}
+}
+
+func TestPathParameters(t *testing.T) {
+	tests := []struct {
+		name  string
+		input *Poller
+		want  []string
+	}{
+		{
+			name:  "multiple parameters",
+			input: &Poller{Prefix: "projects/{project}/zones/{zone}"},
+			want:  []string{"project", "zone"},
+		},
+		{
+			name:  "no parameters",
+			input: &Poller{Prefix: "abc/def"},
+			want:  nil,
+		},
+		{
+			name:  "single parameter",
+			input: &Poller{Prefix: "a/{b}"},
+			want:  []string{"b"},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got := test.input.PathParameters()
+			if diff := cmp.Diff(test.want, got); diff != "" {
+				t.Errorf("PathParameters(%q) mismatch (-want +got):\n%s", test.input.Prefix, diff)
+			}
+		})
+	}
+}

internal/sidekick/config/config.go

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// Package config provides functionality for working with the sidekick.toml
+// configuration file.
 package config
 
 import (

internal/sidekick/config/discovery_test.go

@@ -26,12 +26,11 @@ import (
 
 	"github.com/googleapis/librarian/internal/serviceconfig"
 	"github.com/googleapis/librarian/internal/sidekick/api"
-	"github.com/googleapis/librarian/internal/sidekick/config"
 	"github.com/googleapis/librarian/internal/sidekick/parser/svcconfig"
 )
 
 // NewAPI parses the discovery doc in `contents` and returns the corresponding `api.API` model.
-func NewAPI(serviceConfig *serviceconfig.Service, contents []byte, discoveryConfig *config.Discovery) (*api.API, error) {
+func NewAPI(serviceConfig *serviceconfig.Service, contents []byte, discoveryConfig *api.Discovery) (*api.API, error) {
 	doc, err := newDiscoDocument(contents)
 	if err != nil {
 		return nil, err

internal/sidekick/config/source_roots.go

@@ -26,7 +26,6 @@ import (
 	"github.com/googleapis/librarian/internal/serviceconfig"
 	"github.com/googleapis/librarian/internal/sidekick/api"
 	"github.com/googleapis/librarian/internal/sidekick/api/apitest"
-	"github.com/googleapis/librarian/internal/sidekick/config"
 )
 
 const computeDiscoveryFile = "../../../testdata/discovery/compute.v1.json"
@@ -234,7 +233,7 @@ func ComputeDisco(t *testing.T, sc *serviceconfig.Service) (*api.API, error) {
 	return NewAPI(sc, contents, nil)
 }
 
-func ComputeDiscoWithLros(t *testing.T, discoveryConfig *config.Discovery) (*api.API, error) {
+func ComputeDiscoWithLros(t *testing.T, discoveryConfig *api.Discovery) (*api.API, error) {
 	t.Helper()
 	contents, err := os.ReadFile(computeDiscoveryFile)
 	if err != nil {

internal/sidekick/parser/discovery/discovery.go

@@ -19,10 +19,9 @@ import (
 	"strings"
 
 	"github.com/googleapis/librarian/internal/sidekick/api"
-	"github.com/googleapis/librarian/internal/sidekick/config"
 )
 
-func lroAnnotations(model *api.API, discoveryConfig *config.Discovery) error {
+func lroAnnotations(model *api.API, discoveryConfig *api.Discovery) error {
 	if discoveryConfig == nil {
 		return nil
 	}
@@ -72,7 +71,7 @@ func lroAnnotations(model *api.API, discoveryConfig *config.Discovery) error {
 	return nil
 }
 
-func lroFindPoller(method *api.Method, model *api.API, discoveryConfig *config.Discovery) (*api.Method, []string) {
+func lroFindPoller(method *api.Method, model *api.API, discoveryConfig *api.Discovery) (*api.Method, []string) {
 	var flatPath []string
 	for _, binding := range method.PathInfo.Bindings {
 		flatPath = append(flatPath, binding.PathTemplate.FlatPath())