feat(librariangen): scaffold Java language container for Librarian

.github/workflows/librariangen-ci.yml

@@ -0,0 +1,32 @@
+name: librariangen CI
+
+on:
+  push:
+    branches: [ main ]
+    paths:
+      - 'internal/librariangen/**'
+  pull_request:
+    paths:
+      - 'internal/librariangen/**'
+permissions:
+  contents: read
+
+jobs:
+  test-docker-image:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: "internal/librariangen/go.mod"
+
+      - name: Display Go version
+        run: go version
+
+      - name: Run Go tests
+        run: go test ./...
+        working-directory: internal/librariangen
+

internal/librariangen/Dockerfile

@@ -0,0 +1,65 @@
+# 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
+#
+#     http://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.
+
+# This Dockerfile creates a MOSS-compliant image for the Go librariangen,
+# which is invoked by the Librarian tool. It uses a multi-stage build to
+# create a minimal final image.
+
+# --- Builder Stage ---
+# This stage builds the librariangen binary using the MOSS-compliant base image.
+FROM marketplace.gcr.io/google/debian12:latest AS builder
+
+# Set environment variables for tool versions for easy updates.
+ENV GO_VERSION=1.24.0
+
+# Install build dependencies.
+RUN apt-get update && \
+    apt-get install -y \
+    build-essential \
+    ca-certificates \
+    curl \
+    wget && \
+    rm -rf /var/lib/apt/lists/*
+
+# Install the specific Go version required for compatibility.
+RUN wget https://go.dev/dl/go${GO_VERSION}.linux-amd64.tar.gz -O go.tar.gz && \
+    tar -C /usr/local -xzf go.tar.gz && \
+    rm go.tar.gz
+ENV PATH=/usr/local/go/bin:$PATH
+RUN go version
+
+WORKDIR /src
+
+# Copy go.mod and go.sum to download dependencies before copying all the source.
+# This allows Docker to cache the dependencies layer.
+# COPY go.mod go.sum ./
+# RUN go mod download
+
+# Copy all source code.
+COPY . .
+
+# Build the librariangen binary.
+RUN CGO_ENABLED=0 GOOS=linux go build -v -o /librariangen .
+
+# --- Final Stage ---
+# This stage creates the final, minimal image with the compiled binary and
+# all required runtime dependencies pinned to specific versions for compatibility.
+FROM marketplace.gcr.io/google/debian12:latest
+
+# Copy the compiled librariangen binary from the builder stage.
+COPY --from=builder /librariangen /usr/local/bin/librariangen
+
+# Set the entrypoint for the container to run the compiled librariangen.
+# The Librarian will provide commands like 'generate' as arguments.
+ENTRYPOINT [ "/usr/local/bin/librariangen" ]

internal/librariangen/README.md

@@ -0,0 +1,3 @@
+# Java GAPIC Generator for Librarian (librariangen)
+
+This directory contains the source code for `librariangen`, a containerized Go application that serves as the Java-specific code generator within the Librarian pipeline. Its responsibility is to generate release-ready Java GAPIC client libraries from `googleapis` API definitions, replacing the legacy Java hermetic code generation toolchain.

internal/librariangen/build-docker-and-test.sh

@@ -0,0 +1,32 @@
+#!/bin/bash
+# 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
+#
+#     http://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.
+
+
+set -e
+SCRIPT_DIR=$(dirname "$0")
+IMAGE_NAME="librariangen-test"
+
+echo "Building Docker image..."
+docker build -t "${IMAGE_NAME}" "${SCRIPT_DIR}"
+
+echo "Running version check..."
+output=$(docker run --rm -e GOOGLE_SDK_JAVA_LOGGING_LEVEL=quiet "${IMAGE_NAME}" --version)
+
+if [[ ! "$output" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
+  echo "Version format is incorrect. Got: $output"
+  exit 1
+fi
+
+echo "Version check passed. Version is $output"

internal/librariangen/go.mod

@@ -0,0 +1,3 @@
+module cloud.google.com/java/internal/librariangen
+
+go 1.24.4

internal/librariangen/main.go

@@ -0,0 +1,85 @@
+// 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
+//
+//     http://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 main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log/slog"
+	"os"
+	"strings"
+)
+
+const version = "0.1.0"
+
+// main is the entrypoint for the librariangen CLI.
+func main() {
+	logLevel := slog.LevelInfo
+	switch os.Getenv("GOOGLE_SDK_JAVA_LOGGING_LEVEL") {
+	case "debug":
+		logLevel = slog.LevelDebug
+	case "quiet":
+		logLevel = slog.LevelError + 1
+	}
+	slog.SetDefault(slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
+		Level: logLevel,
+	})))
+	slog.Info("librariangen: invoked", "args", os.Args)
+	if err := run(context.Background(), os.Args[1:]); err != nil {
+		slog.Error("librariangen: failed", "error", err)
+		os.Exit(1)
+	}
+	slog.Info("librariangen: finished successfully")
+}
+
+// run executes the appropriate command based on the CLI's invocation arguments.
+// The idiomatic structure is `librariangen [command] [flags]`.
+func run(ctx context.Context, args []string) error {
+	if len(args) < 1 {
+		return errors.New("librariangen: expected a command")
+	}
+
+	// The --version flag is a special case and not a command.
+	if args[0] == "--version" {
+		fmt.Println(version)
+		return nil
+	}
+
+	cmd := args[0]
+	flags := args[1:]
+
+	if strings.HasPrefix(cmd, "-") {
+		return fmt.Errorf("librariangen: command cannot be a flag: %s", cmd)
+	}
+
+	switch cmd {
+	case "generate":
+		slog.Warn("librariangen: generate command is not yet implemented")
+		return nil
+	case "release-init":
+		slog.Warn("librariangen: release-init command is not yet implemented")
+		return nil
+	case "configure":
+		slog.Warn("librariangen: configure command is not yet implemented")
+		return nil
+	case "build":
+		slog.Warn("librariangen: build command is not yet implemented")
+		return nil
+	default:
+		return fmt.Errorf("librariangen: unknown command: %s (with flags %s)", cmd, flags)
+	}
+
+}

internal/librariangen/main_test.go

@@ -0,0 +1,94 @@
+// 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
+//
+//     http://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 main
+
+import (
+	"context"
+	"testing"
+)
+
+func TestRun(t *testing.T) {
+	ctx := context.Background()
+	tests := []struct {
+		name    string
+		args    []string
+		wantErr bool
+	}{
+		{
+			name:    "no args",
+			args:    []string{},
+			wantErr: true,
+		},
+		{
+			name:    "version flag",
+			args:    []string{"--version"},
+			wantErr: false,
+		},
+		{
+			name:    "flag as command",
+			args:    []string{"--foo"},
+			wantErr: true,
+		},
+		{
+			name:    "unknown command",
+			args:    []string{"foo"},
+			wantErr: true,
+		},
+		{
+			name:    "build command no flags",
+			args:    []string{"build"},
+			wantErr: false,
+		},
+		{
+			name:    "build command with flags",
+			args:    []string{"build", "--repo=.", "--librarian=./.librarian"},
+			wantErr: false,
+		},
+		{
+			name:    "configure command",
+			args:    []string{"configure"},
+			wantErr: false,
+		},
+		{
+			name:    "generate command no flags",
+			args:    []string{"generate"},
+			wantErr: false,
+		},
+		{
+			name:    "generate command with flags",
+			args:    []string{"generate", "--source=.", "--output=./build_out"},
+			wantErr: false,
+		},
+		{
+			name:    "release-init command no flags",
+			args:    []string{"release-init"},
+			wantErr: false,
+		},
+		{
+			name:    "release-init command with flags",
+			args:    []string{"release-init", "--repo=.", "--output=./build_out"},
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Since we are only testing the command dispatching, we can pass a nil
+			// context. The generate function is not actually called.
+			if err := run(ctx, tt.args); (err != nil) != tt.wantErr {
+				t.Errorf("run() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}