feat: Implement XSD Schema Compatibility Checking

[stn1slv]

Summary

This PR implements comprehensive XSD (XML Schema Definition) compatibility checking for the Apicurio Registry, enabling validation of schema evolution according to industry-standard compatibility rules.

Changes

New Features

• ✅ XSD Compatibility Checker - Full implementation supporting all compatibility modes:
  • BACKWARD - Old data readable by new schema
  • FORWARD - New data readable by old schema
  • FULL - Both backward and forward compatible
  • BACKWARD_TRANSITIVE, FORWARD_TRANSITIVE, FULL_TRANSITIVE - Historical version validation
  • NONE - No compatibility checking

Implementation Details

Core Implementation:

• XsdCompatibilityChecker (~715 lines) - Main compatibility checker extending AbstractCompatibilityChecker
• DOM-based XSD parsing with comprehensive element/attribute/type extraction
• Validates schema evolution rules: element/attribute changes, occurrence constraints, type restrictions, enumerations

Key Capabilities:

• Detects backward incompatibilities (adding required elements, removing content, tightening constraints)
• Detects forward incompatibilities (adding optional elements, relaxing constraints, broadening types)
• Validates across entire version history in transitive modes
• Provides detailed error messages with XPath-like context

Modified Files

• schema-util/xsd/src/main/java/io/apicurio/registry/rules/compatibility/XsdCompatibilityChecker.java (NEW)
• schema-util/xsd/src/test/java/io/apicurio/registry/rules/compatibility/XsdCompatibilityCheckerTest.java (NEW)
• schema-util/util-provider/src/main/java/io/apicurio/registry/types/provider/XsdArtifactTypeUtilProvider.java (Modified - 1 method)
• schema-util/xsd/pom.xml (Added JUnit 5 dependency)
• schema-util/xsd/README.md (NEW - Comprehensive documentation)

Testing

Test Coverage

• 20 unit tests with 100% pass rate ✅
• 0 failures, 0 errors, 0 skipped

Test Categories:

• 10 backward compatibility tests (5 compatible, 5 incompatible scenarios)
• 7 forward compatibility tests (3 compatible, 4 incompatible scenarios)
• 2 full compatibility tests
• 1 NONE mode test

Test Scenarios Include:

• Adding/removing optional and required elements
• Adding/removing optional and required attributes
• Changing occurrence constraints (minOccurs, maxOccurs)
• Tightening/loosening type restrictions (numeric ranges, string lengths, patterns)
• Adding/removing enumeration values
• Transitive compatibility validation across version history

Build Status

[INFO] BUILD SUCCESS
[INFO] Tests run: 20, Failures: 0, Errors: 0, Skipped: 0

[Copilot]

Pull Request Overview

This PR implements comprehensive XSD compatibility checking for the Apicurio Registry, enabling validation of schema evolution according to industry-standard compatibility rules.

• Adds full XSD compatibility checker supporting all compatibility modes (BACKWARD, FORWARD, FULL, and TRANSITIVE variants)
• Implements DOM-based XSD parsing with comprehensive element/attribute/type extraction and validation
• Provides 20 comprehensive unit tests covering all compatibility scenarios with 100% pass rate

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
XsdCompatibilityChecker.java	New ~715 line implementation with DOM-based parsing and compatibility validation logic
XsdCompatibilityCheckerTest.java	New comprehensive test suite with 20 tests covering all compatibility modes
XsdArtifactTypeUtilProvider.java	Modified to use new XsdCompatibilityChecker instead of NoopCompatibilityChecker
pom.xml	Added JUnit 5 dependency for testing
README.md	New comprehensive documentation of implementation and usage
assembly-rule-reference.adoc	Updated documentation to reflect XSD compatibility support

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[EricWittmann]

Thanks for the contribution @stn1slv 👍