Scala New Added 26 September 2026

Scala: object X is not a member of package Y

The compiler resolved the package and found nothing of that name inside it, so the import fails rather than the usage. A dependency that is only on the test classpath, a stale target directory after a rename, and a package declaration that no longer matches the artefact all present identically.

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

Quick fix

# Is the dependency on the classpath for this configuration at all
sbt "show Compile/dependencyClasspath" | tr ',' '\n' | grep -i circe
sbt "whatDependsOn io.circe circe-core"

// Test only dependencies are invisible to main sources
libraryDependencies += "org.scalatest" %% "scalatest" % "3.2.19" % Test

// A rename leaves the old class in target until you clean
// sbt clean compile

# What the jar on disk actually contains
unzip -l "$(find ~/.cache/coursier -name 'circe-core_3-*.jar' | head -1)" | grep -i syntax

// The package is the declaration, but it should match the directory
// src/main/scala/com/example/api/Routes.scala
package com.example.api

// A local package of the same name shadows the library, so be absolute
import _root_.com.example.api.Routes

// Scala 3 artefacts are suffixed _3: a _2.13 only library has no such package

How to diagnose 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.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

Check the Scala version suffix on every dependency. Use %% for Scala libraries and plain % only for Java ones.
Run sbt evicted to list dependencies that were evicted by version conflict. A frequent source of runtime NoSuchMethodError.
Use sbt dependencyTree to see the resolved graph and locate the transitive dependency pulling in an old version.
For inference failures, add explicit type annotations at the boundary rather than at the error site; inference failures usually propagate from further up.
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)

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

docs.scala-lang.org scala-sbt.org

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