Unable to use a Provider as an artifact for the maven-publish plugin

[Adrodoc]

Using a Provider as an artifact for the maven-publish-Plugin does not work in Gradle 5.6 anymore. Using a File instance still works despite the error message (see current behaviour) suggesting otherwise.

Expected Behavior

The file my-artifact.txt should be published into the local maven repository.

Current Behavior

You get the following error:

FAILURE: Build failed with an exception.

* What went wrong:
Could not determine the dependencies of task ':publishArtifactoryPublicationToMavenLocal'.
> Cannot convert C:\...\gradle-issue-11054\my-artifact.txt to a task.
  The following types/formats are supported:
    - A Task instance
    - A TaskReference instance
    - A Buildable instance
    - A TaskDependency instance
    - A Provider that represents a task output
    - A Provider instance that returns any of these types
    - A Closure instance that returns any of these types
    - A Callable instance that returns any of these types
    - An Iterable, Collection, Map or array instance that contains any of these types

Context

This works in Gradle 5.5.1 and below, but stops working in Gradle 5.6.

Steps to Reproduce

Execute gradlew publishToMavenLocal in this project: gradle-issue-11054.zip

For reference here is the build.gradle:

apply plugin: 'maven-publish'

wrapper { gradleVersion = '5.6' }

group = 'org.gradle'
ext.artifactId = 'issue-11054'
version = '1.0.0'

publishing {
  publications {
    artifactory(MavenPublication) {
      artifactId = project.artifactId
      // Works in Gradle 5.5.1 and Gradle 5.6
//      artifact file('my-artifact.txt')

      // Works in Gradle 5.5.1 but not Gradle 5.6
      artifact provider{ file('my-artifact.txt') }
    }
  }
}

Your Environment

user@PC MINGW64 /c/.../gradle-issue-11054
$ ./gradlew -v

------------------------------------------------------------
Gradle 5.6
------------------------------------------------------------

Build time:   2019-08-14 21:05:25 UTC
Revision:     f0b9d60906c7b8c42cd6c61a39ae7b74767bb012

Kotlin:       1.3.41
Groovy:       2.5.4
Ant:          Apache Ant(TM) version 1.9.14 compiled on March 12 2019
JVM:          1.8.0_162 (Oracle Corporation 25.162-b12)
OS:           Windows 7 6.1 amd64

[jjohannes]

Thanks for reporting this @Adrodoc. This is indeed a regression caused by the combination of #9467 and #6775 I believe. Fix is in the making.

[jjohannes]

The fix on master for 6.1

Keeping this open in case there is a 6.0.1- pick 62cfd99

[jjohannes]

Picked to release for 6.0.1