Required fields lead to non required element in XSD

[kwin]

E.g. the required field prefix from https://github.com/apache/maven/blob/master/maven-repository-metadata/src/main/mdo/metadata.mdo#L354-L360 leads to this XSD:

<xs:element minOccurs="0" name="prefix" type="xs:string">

Obsviously the element with name prefix must leave out minOccurs="0" to be required in the XMLs.

[michael-o]

Please link the spot in question. I have provided it in the JIRA issue.

[kwin]

This seems to be caused by

modello/modello-plugins/modello-plugin-xsd/src/main/java/org/codehaus/modello/plugin/xsd/XsdGenerator.java

Lines 245 to 247 in 8467ab8

	// Usually, would only do this if the field is not "required", but due to inheritance, it may be
	// present, even if not here, so we need to let it slide
	w.addAttribute( "minOccurs", "0" );

.

[kwin]

The reason for this behaviour seems to be driven by pom.xml specifics, i.e. POMs are merged with their parents before they need to be valid. As this is definitely an edge case Modello should have a flag for enabling/disabling that behaviour.
By default it is reasonable to assume that the XML is not requiring post-processing before validating it against the schema.

[michael-o]

The reason for this behaviour seems to be driven by pom.xml specifics, i.e. POMs are merged with their parents before they need to be valid. As this is definitely an edge case Modello should have a flag for enabling/disabling that behaviour. By default it is reasonable to assume that the XML is not requiring post-processing before validating it against the schema.

I fully agree with that.