[PR] MNG-8174: Fix NPE when a property references itself in a plugin configuration [maven]

["elharo (via GitHub)" <gi...@apache.org>]

elharo opened a new pull request, #12932:
URL: https://github.com/apache/maven/pull/12932

   Fixes #10598 (MNG-8174)
   
   ### Problem
   When a POM property references itself (e.g. `<prop>${prop}</prop>`) and that
   property is also used inside a plugin configuration attribute such as
   `<filter token="key" value="${prop}"/>`, invoking the model interpolation
   throws
   
   ```
   java.lang.NullPointerException: Attribute value can not be null
       at org.codehaus.plexus.util.xml.Xpp3Dom.setAttribute(Xpp3Dom.java:179)
       at ...StringVisitorModelInterpolator$ModelVisitor.visit(StringVisitorModelInterpolator.java:727)
   ```
   
   A recursive expression cycle is detected by the interpolator, which then
   returns `null` for the unresolved expression. `visit(Xpp3Dom)` in
   `StringVisitorModelInterpolator` unconditionally called
   `dom.setAttribute(attr, val)` (and `dom.setValue(val)`) even when the
   interpolated value was `null`, causing the NPE. The `visit(Properties)`
   method already guarded against `null` in the identical situation.
   
   ### Fix
   When interpolation of an Xpp3Dom content value or attribute returns `null`
   (which happens on a recursive expression cycle), leave the original value
   untouched instead of writing `null` into the DOM. This mirrors the existing
   guard in `visit(Properties)`.
   
   ### Test
   Added `testRecursiveExpressionCycleInPluginConfiguration` to
   `AbstractModelInterpolatorTest`, which builds a model with a
   self-referencing property and a plugin configuration attribute referencing
   it. Before the fix the test fails with the NPE above; after the fix the
   interpolation completes, reports the recursive-expression-cycle error and
   the attribute keeps its original value.


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Re: [PR] [MNG-8174] Fix NPE when a property references itself in a plugin configuration [maven]

["elharo (via GitHub)" <gi...@apache.org>]

elharo merged PR #12932:
URL: https://github.com/apache/maven/pull/12932


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Re: [PR] [MNG-8174] Fix NPE when a property references itself in a plugin configuration [maven]

["github-actions[bot] (via GitHub)" <gi...@apache.org>]

github-actions[bot] commented on PR #12932:
URL: https://github.com/apache/maven/pull/12932#issuecomment-5468605127

   @elharo Please assign appropriate label to PR according to the type of change.


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