Scala Compiler flags for 2.13. Based on Tpolecat's 2.12 version

scalac-compiler-flags-2.13.sbt

scalacOptions ++= Seq(
        "-deprecation",                      // Emit warning and location for usages of deprecated APIs.
        "-encoding", "utf-8",                // Specify character encoding used by source files.
        "-explaintypes",                     // Explain type errors in more detail.
        "-feature",                          // Emit warning and location for usages of features that should be imported explicitly.
        "-language:existentials",            // Existential types (besides wildcard types) can be written and inferred
        //  "-language:experimental.macros",   // Allow macro definition (besides implementation and application). Disabled, as this will significantly change in Scala 3
        "-language:higherKinds",             // Allow higher-kinded types
        //  "-language:implicitConversions",   // Allow definition of implicit functions called views. Disabled, as it might be dropped in Scala 3. Instead use extension methods (implemented as implicit class Wrapper(val inner: Foo) extends AnyVal {}
        "-unchecked",                        // Enable additional warnings where generated code depends on assumptions.
        "-Xcheckinit",                       // Wrap field accessors to throw an exception on uninitialized access.
        "-Xfatal-warnings",                  // Fail the compilation if there are any warnings.

        "-Xlint:adapted-args",               // Warn if an argument list is modified to match the receiver.
        "-Xlint:constant",                   // Evaluation of a constant arithmetic expression results in an error.
        "-Xlint:delayedinit-select",         // Selecting member of DelayedInit.
        "-Xlint:doc-detached",               // A Scaladoc comment appears to be detached from its element.
        "-Xlint:inaccessible",               // Warn about inaccessible types in method signatures.
        "-Xlint:infer-any",                  // Warn when a type argument is inferred to be `Any`.
        "-Xlint:missing-interpolator",       // A string literal appears to be missing an interpolator id.
        "-Xlint:nullary-override",           // Warn when non-nullary `def f()' overrides nullary `def f'.
        "-Xlint:nullary-unit",               // Warn when nullary methods return Unit.
        "-Xlint:option-implicit",            // Option.apply used implicit view.
        "-Xlint:package-object-classes",     // Class or object defined in package object.
        "-Xlint:poly-implicit-overload",     // Parameterized overloaded implicit methods are not visible as view bounds.
        "-Xlint:private-shadow",             // A private field (or class parameter) shadows a superclass field.
        "-Xlint:stars-align",                // Pattern sequence wildcard must align with sequence component.
        "-Xlint:type-parameter-shadow",      // A local type parameter shadows a type already in scope.
        "-Xlint:unused",                     // TODO check if we still need -Wunused below
        "-Xlint:nonlocal-return",            // A return statement used an exception for flow control.
        "-Xlint:implicit-not-found",         // Check @implicitNotFound and @implicitAmbiguous messages.
        "-Xlint:serial",                     // @SerialVersionUID on traits and non-serializable classes.
        "-Xlint:valpattern",                 // Enable pattern checks in val definitions.
        "-Xlint:eta-zero",                   // Warn on eta-expansion (rather than auto-application) of zero-ary method.
        "-Xlint:eta-sam",                    // Warn on eta-expansion to meet a Java-defined functional interface that is not explicitly annotated with @FunctionalInterface.
        "-Xlint:deprecation",                // Enable linted deprecations.

        "-Wdead-code",                       // Warn when dead code is identified.
        "-Wextra-implicit",                  // Warn when more than one implicit parameter section is defined.
        "-Wmacros:both",                     // Lints code before and after applying a macro
        "-Wnumeric-widen",                   // Warn when numerics are widened.
        "-Woctal-literal",                   // Warn on obsolete octal syntax.
        "-Wself-implicit",                   // Warn when an implicit resolves to an enclosing self-definition.
        "-Wunused:imports",                  // Warn if an import selector is not referenced.
        "-Wunused:patvars",                  // Warn if a variable bound in a pattern is unused.
        "-Wunused:privates",                 // Warn if a private member is unused.
        "-Wunused:locals",                   // Warn if a local definition is unused.
        "-Wunused:explicits",                // Warn if an explicit parameter is unused.
        "-Wunused:implicits",                // Warn if an implicit parameter is unused.
        "-Wunused:params",                   // Enable -Wunused:explicits,implicits.
        "-Wunused:linted",
        "-Wvalue-discard",                   // Warn when non-Unit expression results are unused.

        "-Ybackend-parallelism", "8",                 // Enable paralellisation — change to desired number!
        "-Ycache-plugin-class-loader:last-modified",  // Enables caching of classloaders for compiler plugins
        "-Ycache-macro-class-loader:last-modified",   // and macro definitions. This can lead to performance improvements.

    )

Thanks for hosting, this, Tamer!