Add default namespace prefix for simple type references in generated XSDs

[klasfahlberg]

This patch addresses an issue where schemagen does not generate the default namespace prefix for references to simple types (such as enum types), resulting in XSDs that are not fully compatible with xjc. The following changes were made:

Added logic to detect element references without a namespace prefix and prepend the default namespace prefix where appropriate.

• Updated ChangeNamespacePrefixProcessor to handle these cases and ensure compatibility.
• Adjusted SimpleNamespaceResolver to avoid overwriting the tns prefix and improve prefix/URI mapping safety.
• Minor update in XsdGeneratorHelper to prevent unnecessary prefix substitutions.

These changes ensure that generated XSDs include the correct namespace prefixes, improving compatibility with tools expecting explicit prefixes.

These two PR:s, written by a former colleague, are no longer relevant and can be closed.

• Fixes #141 #142
• SimpleRegexFileFilter #144

[slachiewicz]

Could You try to add some tests?

[xdy]

Added some tests from Klas.

[klasfahlberg]

slachiewicz Are the added tests sufficient?

[Copilot]

Pull Request Overview

This PR addresses namespace prefix issues in generated XSD files to improve compatibility with xjc by ensuring simple type references (like enums) include appropriate default namespace prefixes.

• Enhanced ChangeNamespacePrefixProcessor to detect and prefix unprefixed element references in the default namespace (tns)
• Improved SimpleNamespaceResolver to preserve "tns" prefix mappings and handle prefix conflicts more safely
• Added validation in XsdGeneratorHelper to prevent unnecessary prefix substitutions

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
SimpleNamespaceResolver.java	Added logic to preserve "tns" prefix and handle prefix/URI mapping conflicts
ChangeNamespacePrefixProcessor.java	Added detection and prefixing of unprefixed element references for default namespace
XsdGeneratorHelper.java	Added check to prevent unnecessary prefix substitutions when old and new prefixes are identical
SimpleNamespaceResolverTest.java	Added comprehensive tests for "tns" prefix preservation and conflict detection
ChangeNamespacePrefixProcessorTest.java	Added tests for element reference prefixing behavior

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

The variable oldPrefix is retrieved but not used in the main logic flow within the if block. Consider retrieving it only when needed or clarify its purpose with better variable naming.

Suggested change

	String oldPrefix = uri2Prefix.get(nodeValue);
	if (oldPrefix == null || !oldPrefix.equals("tns")) {
	if (uri2Prefix.get(nodeValue) == null || !uri2Prefix.get(nodeValue).equals("tns")) {

[Copilot]

Corrected spelling of 'simpletypes' to 'simple types' and 'XSD:s' to 'XSDs'.

Suggested change

	// simpletypes, such as enum types => we want to add the default namespace prefix to those nodes in
	// order to get xjc-compatible XSD:s
	// simple types, such as enum types => we want to add the default namespace prefix to those nodes in
	// order to get xjc-compatible XSDs