feat(internal/serviceconfig): import gapic yaml configs from googleapis

Add a GAPICYaml field to the API struct in sdk.yaml that holds all
configuration previously stored in *_gapic.yaml files in googleapis.
This includes Java-specific settings (package name, interface names) and
language-neutral settings (LRO polling, batching). Java-specific fields
have TODOs to move them to librarian.yaml later.

An import-gapic-yaml subcommand is added to the importconfigs tool. It
reads all *_gapic.yaml files from a local googleapis checkout and merges
their data into existing sdk.yaml entries. APIs not already in sdk.yaml
are skipped. 69 of 79 gapic yaml files were imported; 10 were skipped
because their API paths are not in the allowlist.

For #3041

Author: julieqiu

doc/api-allowlist-schema.md

@@ -20,3 +20,62 @@ This document describes the schema for the API Allowlist.
 | `service_name` | string | Is a DNS-like logical identifier for the service, such as `calendar.googleapis.com`. |
 | `title` | string | Overrides the API title from the service config. |
 | `transports` | map[string]Transport | Defines the supported transports per language. Map key is the language name (e.g., "python", "rust"). Optional. If omitted, all languages use GRPCRest by default. |
+| `gapic_yaml` | [GAPICYamlConfig](#gapicyamlconfig-configuration) (optional) | Contains configuration imported from *_gapic.yaml files in googleapis. |
+
+## GAPICBatchDescriptor Configuration
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| `batched_field` | string |  |
+| `discriminator_fields` | list of string |  |
+| `subresponse_field` | string |  |
+
+## GAPICBatching Configuration
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| `thresholds` | [GAPICBatchingThresholds](#gapicbatchingthresholds-configuration) (optional) |  |
+| `batch_descriptor` | [GAPICBatchDescriptor](#gapicbatchdescriptor-configuration) (optional) |  |
+
+## GAPICBatchingThresholds Configuration
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| `element_count_threshold` | int |  |
+| `request_byte_threshold` | int |  |
+| `delay_threshold_millis` | int |  |
+| `flow_control_element_limit` | int |  |
+| `flow_control_byte_limit` | int |  |
+| `flow_control_limit_exceeded_behavior` | string |  |
+
+## GAPICInterface Configuration
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| `name` | string |  |
+| `methods` | list of [GAPICMethod](#gapicmethod-configuration) |  |
+
+## GAPICLongRunning Configuration
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| `initial_poll_delay_millis` | int64 |  |
+| `poll_delay_multiplier` | float64 |  |
+| `max_poll_delay_millis` | int64 |  |
+| `total_poll_timeout_millis` | int64 |  |
+
+## GAPICMethod Configuration
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| `name` | string |  |
+| `long_running` | [GAPICLongRunning](#gapiclongrunning-configuration) (optional) |  |
+| `batching` | [GAPICBatching](#gapicbatching-configuration) (optional) |  |
+
+## GAPICYamlConfig Configuration
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| `java_package_name` | string | Is the Java package name. TODO(https://github.com/googleapis/librarian/issues/3041): move to librarian.yaml. |
+| `java_interface_names` | map[string]string | Maps fully-qualified interface names to short Java class names. TODO(https://github.com/googleapis/librarian/issues/3041): move to librarian.yaml. |
+| `interfaces` | list of [GAPICInterface](#gapicinterface-configuration) | Contains language-neutral per-interface, per-method configuration including long-running operation polling settings and batching config. |

internal/serviceconfig/api.go

@@ -115,6 +115,10 @@ type API struct {
 	// Map key is the language name (e.g., "python", "rust").
 	// Optional. If omitted, all languages use GRPCRest by default.
 	Transports map[string]Transport `yaml:"transports,omitempty"`
+
+	// GAPICYaml contains configuration imported from *_gapic.yaml files in
+	// googleapis.
+	GAPICYaml *GAPICYamlConfig `yaml:"gapic_yaml,omitempty"`
 }
 
 // Transport gets transport for a given language.

internal/serviceconfig/gapic_yaml.go

@@ -0,0 +1,79 @@
+// Copyright 2026 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 serviceconfig
+
+// GAPICYamlConfig contains all configuration imported from a *_gapic.yaml
+// file. This groups Java-specific and language-neutral settings so they can
+// be written together to a single file during generation.
+type GAPICYamlConfig struct {
+	// JavaPackageName is the Java package name.
+	// TODO(https://github.com/googleapis/librarian/issues/3041): move to librarian.yaml.
+	JavaPackageName string `yaml:"java_package_name,omitempty"`
+
+	// JavaInterfaceNames maps fully-qualified interface names to short
+	// Java class names.
+	// TODO(https://github.com/googleapis/librarian/issues/3041): move to librarian.yaml.
+	JavaInterfaceNames map[string]string `yaml:"java_interface_names,omitempty"`
+
+	// Interfaces contains language-neutral per-interface, per-method
+	// configuration including long-running operation polling settings and
+	// batching config.
+	Interfaces []GAPICInterface `yaml:"interfaces,omitempty"`
+}
+
+// GAPICInterface represents a service interface with method-level config
+// imported from *_gapic.yaml files in googleapis.
+type GAPICInterface struct {
+	Name    string        `yaml:"name"`
+	Methods []GAPICMethod `yaml:"methods,omitempty"`
+}
+
+// GAPICMethod represents method-level configuration from a gapic yaml file.
+type GAPICMethod struct {
+	Name        string            `yaml:"name"`
+	LongRunning *GAPICLongRunning `yaml:"long_running,omitempty"`
+	Batching    *GAPICBatching    `yaml:"batching,omitempty"`
+}
+
+// GAPICLongRunning contains polling configuration for long-running operations.
+type GAPICLongRunning struct {
+	InitialPollDelayMillis int64   `yaml:"initial_poll_delay_millis,omitempty"`
+	PollDelayMultiplier    float64 `yaml:"poll_delay_multiplier,omitempty"`
+	MaxPollDelayMillis     int64   `yaml:"max_poll_delay_millis,omitempty"`
+	TotalPollTimeoutMillis int64   `yaml:"total_poll_timeout_millis,omitempty"`
+}
+
+// GAPICBatching contains request batching configuration.
+type GAPICBatching struct {
+	Thresholds      *GAPICBatchingThresholds `yaml:"thresholds,omitempty"`
+	BatchDescriptor *GAPICBatchDescriptor    `yaml:"batch_descriptor,omitempty"`
+}
+
+// GAPICBatchingThresholds defines when batching should occur.
+type GAPICBatchingThresholds struct {
+	ElementCountThreshold            int    `yaml:"element_count_threshold,omitempty"`
+	RequestByteThreshold             int    `yaml:"request_byte_threshold,omitempty"`
+	DelayThresholdMillis             int    `yaml:"delay_threshold_millis,omitempty"`
+	FlowControlElementLimit          int    `yaml:"flow_control_element_limit,omitempty"`
+	FlowControlByteLimit             int    `yaml:"flow_control_byte_limit,omitempty"`
+	FlowControlLimitExceededBehavior string `yaml:"flow_control_limit_exceeded_behavior,omitempty"`
+}
+
+// GAPICBatchDescriptor describes how requests should be batched together.
+type GAPICBatchDescriptor struct {
+	BatchedField        string   `yaml:"batched_field,omitempty"`
+	DiscriminatorFields []string `yaml:"discriminator_fields,omitempty"`
+	SubresponseField    string   `yaml:"subresponse_field,omitempty"`
+}