nathansgreen / slf4j-compatibility-suite

Ensure slf4j-api retains source and binary compatibility

slf4j-compatibility-suite

Ensure slf4j-api retains source and binary compatibility with the addition of Java 8 lambda support.

Tested against (so far):

• slf4j-simple 1.7.12
• slf4j-simple 1.6.6
• Logback 1.0.1

No artifacts from this suite should end up in a user's local repository, so long as the install command is not given to Maven.

Running

The best way to run a build is as follows:

mvn clean verify -Dit-repo-directory=`pwd`/it/target/it-repo

This will cause all dependencies required by the integration tests to be copied into the it/target/it-repo directory, ensuring isolation from the local repository. The default execution works, but will write to a temp directory which may not be cleaned up in a timely fashion. Example:

mvn clean verify

Compatibility notes

Virtually all uses of the SLF4J API should be source and binary compatible, with the exception of direct use of the null keyword for arguments. Example:

logger.info("message", null);

Direct use of the null keyword is not source-compatible due to overloading restrictions. While it is highly probable that real-world cases of this sort of code do exist, those cases are probably very rare. It is even less likely that those cases have a sane rationale for their existence.

Lambdas that throw exceptions are the major source of (potential) runtime incompatibility. If the process of evaluating the lambdas does not catch exceptions (similar to what is done in org.slf4j.helpers.MessageFormatter) then logging operations can fail. Whether this is ultimately allowed will be a design choice agreed upon by the project lead(s). The best option is probably to be completely safe and allow implementers of the API to override the default behavior to be more inline with their own style and performance goals.

Backporting

Thanks to the Retrolambda project, it is possible to run code that uses the Java 8 lambda features on older JREs, as long as dependencies are carefully managed. The Logger API is therefore safe to use, and a test module in this suite is present as a proof of concept. The [maven plugin] (http://orfjackal.github.io/retrolambda/retrolambda-maven-plugin/plugin-info.html) is a good starting point for those who want to use lambdas but execute under older implementations of Java.