Since Gradle 7.0 this is not a warning any more, it's an error which causes the build to break:
What went wrong:
A problem was found with the configuration of task ':asciidoctorPdf' (type 'AsciidoctorPdfTask').
In plugin 'org.asciidoctor.jvm.pdf' type 'org.asciidoctor.gradle.jvm.pdf.AsciidoctorPdfTask' property 'fontsDir' is missing an input or output annotation.
Reason: A property without annotation isn't considered during up-to-date checking.
Since Gradle 7.0 this is not a warning any more, it's an error which causes the build to break:
What went wrong: A problem was found with the configuration of task ':asciidoctorPdf' (type 'AsciidoctorPdfTask').
Reason: A property without annotation isn't considered during up-to-date checking.
Possible solutions:
Please refer to https://docs.gradle.org/7.2/userguide/validation_problems.html#missing_annotation for more details about this problem.
https://github.com/asciidoctor/asciidoctor-gradle-plugin/blob/master/jvm-pdf/src/main/groovy/org/asciidoctor/gradle/jvm/pdf/AsciidoctorPdfTask.groovy sais this property is deprecated and you should use the plural (fontsDirs) instead which is annotated which @InputFiles.
But just the presence of the deprecated field without annotation breaks the build.
With Gradle 6.7.2 it works fine.