Directory variable interpolation of ${project.build.testResources} doesn't work properly

[gerib]

See https://stackoverflow.com/questions/53042572/directory-variable-interpolation-of-project-build-testresources-doesnt-work ... which got deleted due to SE's deletion model recently so here it is to the full now:

I have a wagon-maven-plugin under Maven 3.5.4 in my <build>/<plugins> section with:

    <fromDir>${project.build.testResources}</fromDir>
    <includes>file</includes>

This interpolates to:

[INFO] --- wagon-maven-plugin:2.0.0:upload (publish-to-integration-test) @ <project> ---
...
[DEBUG]   (f) fromDir = <project path>\[
  Resource {targetPath: null, filtering: false,
    FileSet {directory: <project path>\src\test\resources,
      PatternSet [includes: {}, excludes: {}]}}]
[DEBUG]   (f) includes = file
...

Note the empty includes: {}!

The result is:

[INFO] Nothing to upload.

It works if I change <fromDir> to the explicit path string.

If I use <fromDir>${project.build.directory}</fromDir> in another POM it is reasonably not interpolated to a Resource object but to a simple path string:

[DEBUG]   (f) fromDir = <project path>\target

and hence works there, too.

Is this a bug or a feature of ${project.build.testResources}? But, if it is a feature, what the f...heck is it for?

UPDATE

I created an according issue on GitHub.

[dantran]

looks to me Maven not interpolate ${project.build.testResources} at your pom, use ${project.build.directory}/xxxx instead