Merge pull request #224 from domaframework/docs/claude

Add CLAUDE.md for Claude Code guidance

Author: nakamura-to

CLAUDE.md

@@ -0,0 +1,93 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Doma CodeGen Plugin is a Gradle plugin that generates Java, Kotlin, and SQL files from database schemas. It's part of the Doma framework ecosystem and supports Doma 3.
+
+## Build Commands
+
+```bash
+# Build entire project with code formatting
+./gradlew spotlessApply build
+
+# Build only the plugin module
+./gradlew :codegen:build
+
+# Clean build
+./gradlew clean build
+```
+
+## Testing Commands
+
+```bash
+# Run all tests
+./gradlew test
+
+# Run specific module tests
+./gradlew :codegen:test
+./gradlew :codegen-test:test
+
+# Test code generation (from codegen-test directory)
+cd codegen-test
+./gradlew domaCodeGenJavaAll build
+./gradlew domaCodeGenKotlinAll build
+```
+
+## Code Quality
+
+```bash
+# Apply code formatting (required before commits)
+./gradlew spotlessApply
+
+# Check code formatting
+./gradlew spotlessCheck
+```
+
+## Architecture Overview
+
+### Multi-Module Structure
+- **codegen**: Main plugin implementation
+  - Plugin entry point: `CodeGenPlugin.java`
+  - Tasks defined in `org.seasar.doma.gradle.codegen.task` package
+  - Code generators in `org.seasar.doma.gradle.codegen.generator` package
+  - Database dialects in `org.seasar.doma.gradle.codegen.dialect` package
+
+- **codegen-test**: Integration test project demonstrating plugin usage
+
+### Key Components
+
+1. **Code Generators**: Transform database metadata into Java/Kotlin code using FreeMarker templates
+   - `JavaGenerator`: Generates Java entities and DAOs
+   - `KotlinGenerator`: Generates Kotlin entities and DAOs
+   - `SqlGenerator`: Generates SQL template files
+
+2. **Database Dialects**: Database-specific implementations for metadata extraction
+   - Supports: H2, MySQL, Oracle, PostgreSQL, SQL Server, DB2, HSQLDB
+
+3. **Gradle Tasks**: Plugin provides tasks prefixed with `domaCodeGen`
+   - Pattern: `domaCodeGen{Java|Kotlin|Sql}{EntityName|All}`
+
+4. **Template System**: FreeMarker templates in `/codegen/src/main/resources/`
+   - Customizable via `templateDir` configuration
+
+### Development Notes
+
+- Minimum Java version: 17
+- Uses Gradle Kotlin DSL for build configuration
+- JUnit 5 for testing
+- Google Java Format for code style (enforced via Spotless)
+- Plugin ID: `org.domaframework.doma.codegen`
+- Current version: Check `gradle.properties`
+
+### Database Connection
+
+The plugin connects to databases to read metadata. Configure in build.gradle:
+```kotlin
+domaCodeGen {
+    url = "jdbc:h2:mem:example"
+    user = "sa"
+    password = ""
+}
+```