scala-steward / sbt-sammy

A floating threshold for compiler warnings

sbt-sammy

A friendly policeman to help reduce your compiler warnings.

Tomorrow the sun will come up again, and I'm pretty sure that whatever happens we won't have found Freedom, and there won't be a whole lot of Justice, and I'm damn sure we won't have found Truth. But it's just possible that I might get a hard-boiled egg. -- Sam Vimes, Night Watch by Terry Pratchett

In a perfect world, all projects would start off life with @tpolecat's scala compiler options and we would never encounter compiler warnings. In reality, we have to delve into mature, imperfect codebases where the lofty heights of Xfatal-warnings are difficult to achieve. We have to take a pragmatic approach to cleaning these up.

sbt-sammy prevents you from making your codebase worse by enforcing a warning threshold. This threshold decreases whenever you make improvements, nudging you to take small steps to -Xfatal-warnings.

To use

This plugin requires sbt 1.0+.

Add this to your project/plugins.sbt or as a global plugin in ~/.sbt/1.0/plugins/plugins.sbt:

addSbtPlugin("com.github.zainab-ali" % "sbt-sammy" % version)

Where version is set to the latest version of sbt-sammy

Setup

With a floating threshold (recommended)

sbt-sammy can reduce its warning threshold to the maximum number of warnings in your codebase. This means that each time you make a positive change, you can reduce your warning threshold.

If you want to do this, simply run sbt policeWarnings. The warning threshold should decrease to the maximum number of warnings in your project.

With a fixed threshold

If you would like to enforce a fixed threshold that sbt-sammy won't reduce then add the following to your build.sbt:

sammyWarningThresholdFile := None
sammyWarningThreshold := yourFixedThreshold

With suggestions

sbt-sammy is geared towards incremental fixes, and can suggest files to be fixed. It does this by diffing the files with warnings with those in a changeset. You need to supply it with a sammyDiffCommand that generates a list of changed files.

For example, if you would like to look for changes between the current branch and the master:

sammyDiffCommand := Some("git diff --name-only master...HEAD")

Run

Run sbt policeWarnings. This task will fail if the number of warnings exceeds the threshold.