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FixMyError.net
Scala 6 errors

Scala & sbt Errors

Dependency resolution, binary compatibility and type inference failures.

Understanding Scala errors

Scala's most distinctive error class is binary incompatibility: libraries are published per Scala major version, and mixing artifacts built for different versions produces confusing "not a member of" or NoSuchMethodError failures. The %% operator in sbt exists precisely to append the right suffix, and most unresolved-dependency errors are a % where %% was needed.

How to debug Scala errors

  1. Check the Scala version suffix on every dependency. Use %% for Scala libraries and plain % only for Java ones.
  2. Run sbt evicted to list dependencies that were evicted by version conflict. A frequent source of runtime NoSuchMethodError.
  3. Use sbt dependencyTree to see the resolved graph and locate the transitive dependency pulling in an old version.
  4. For inference failures, add explicit type annotations at the boundary rather than at the error site; inference failures usually propagate from further up.
  5. Clear stale state with sbt clean and remove ~/.ivy2/cache or ~/.cache/coursier entries only for the specific failing artifact.

Tools worth reaching for

  • sbt evicted
  • sbt dependencyTree
  • coursier resolve
  • scalac -explain
  • MiMa (binary compat checks)

All 6 Scala errors

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