Added scala compiler options

Author: Michal Bogacz

.bazelrc

@@ -1,2 +1,5 @@
 common --java_language_version=17
 common --java_runtime_version=17
+
+# useful for CI:
+# build --flaky_test_attempts=2

BUILD.bazel

@@ -0,0 +1,15 @@
+load("@io_bazel_rules_scala//scala:scala.bzl", "setup_scala_toolchain")
+
+setup_scala_toolchain(
+    name = "custom_scala_toolchain",
+    scalacopts = [
+        "-Wunused",  # Warn if an a construct is unused.
+        "-Wdead-code",  # Warn when dead code is identified.
+        "-Xlint:inaccessible",  # Warn about inaccessible types in method signatures.
+        "-feature",
+        "-Ymacro-annotations",
+        "-Werror",
+    ],
+    strict_deps_mode = "error",
+    unused_dependency_checker_mode = "off",
+)

WORKSPACE.bazel

@@ -8,9 +8,11 @@ http_archive(
 )
 
 load("@io_bazel_rules_scala//:scala_config.bzl", "scala_config")
+
 scala_config(scala_version = "2.13.14")
 
 load("@io_bazel_rules_scala//scala:scala.bzl", "scala_repositories")
+
 scala_repositories(
     overriden_artifacts = {
         # Change both the artifact names and sha256s.
@@ -30,12 +32,17 @@ scala_repositories(
 )
 
 load("@rules_proto//proto:repositories.bzl", "rules_proto_dependencies", "rules_proto_toolchains")
+
 rules_proto_dependencies()
+
 rules_proto_toolchains()
 
 load("@io_bazel_rules_scala//scala:toolchains.bzl", "scala_register_toolchains")
-scala_register_toolchains()
+
+register_toolchains(":custom_scala_toolchain")
 
 load("@io_bazel_rules_scala//testing:scalatest.bzl", "scalatest_repositories", "scalatest_toolchain")
+
 scalatest_repositories()
+
 scalatest_toolchain()