[ARCHETYPE-566] Partial archetype fails on existing structure

**[Pierre Remazeilles](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=peteus)** opened **[ARCHETYPE-566](https://issues.apache.org/jira/browse/ARCHETYPE-566?redirect=false)** and commented

Greetings,

When generating a partial archetype on an existing project which already contains some of its files, the generation fails with the message "Don't override file".

However, given the code, the generation should not fail in this case, but rather display a warning message. It seems the problem lies in the fact that the "failIfExists" parameter is inverted in the methods "processArchetypeTemplates" and "processArchetypeTemplatesWithWarning". I think "failIfExists" should be false for "processArchetypeTemplatesWithWarning" (as the method name would imply), and true for "processArchetypeTemplates". This is currently the opposite.

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**Affects:** 3.1.0

Locate the processArchetypeTemplates and processArchetypeTemplatesWithWarning methods in the Maven Archetype plugin and trace how they pass failIfExists during partial generation. Reproduce generation against an existing project with overlapping files, then verify that the warning path no longer fails while the normal path retains its intended failure behavior.

Written by the indexing model from the issue text.