A few examples

Author: aszady

examples/crossbuild/1_single/BUILD

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+load("@io_bazel_rules_scala//scala:scala.bzl", "scala_binary", "scala_library", "scala_test")
+
+# Here we demonstrate the simplest case,
+# single binary, test or library for which we set a specific version or use the default one:
+
+# This one will be compiled by 2.11 compiler:
+scala_library(
+    name = "lib211",
+    srcs = ["lib.scala"],
+    scala_version = "2.11.12",
+)
+
+# This one will be compiled by 2.13 compiler:
+scala_test(
+    name = "test213",
+    srcs = ["test.scala"],
+    scala_version = "2.13.12",
+)
+
+# This one will be compiled by 3.3 compiler (the default one):
+scala_binary(
+    name = "bin33",
+    srcs = ["bin.scala"],
+    main_class = "X",
+)

examples/crossbuild/1_single/bin.scala

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+object C extends App {
+  println("Hello")
+}

examples/crossbuild/1_single/lib.scala

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+class A

examples/crossbuild/1_single/test.scala

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+import org.scalatest.flatspec.AnyFlatSpec
+
+class Zero extends AnyFlatSpec {
+  "Equality" should "be tested" in {
+    assert (0 == -0)
+  }
+}

examples/crossbuild/2_deps/BUILD

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+load("@io_bazel_rules_scala//scala:scala.bzl", "scala_binary", "scala_library")
+
+# Here we demonstrate how scala_version is propagated through deps.
+
+# This one will always be compiled by 2.11 compiler:
+scala_library(
+    name = "lib211",
+    srcs = ["lib.scala"],
+    scala_version = "2.11.12",
+)
+
+# This one will be compiled by 3.3 compiler (unless requested otherwise)
+scala_library(
+    name = "lib",
+    srcs = ["lib_default.scala"],
+)
+
+scala_binary(
+    name = "bin213",
+    srcs = ["bin.scala"],  # compiled with 2.13 (as per `scala_version`)
+    main_class = "C",
+    scala_version = "2.13.12",
+    deps = [
+        ":lib",  # compiled 2.13 (as per `scala_version`)
+        ":lib211",  # compiled with 2.11 (that target overrides version)
+    ],
+)
+
+scala_binary(
+    name = "bin33",
+    srcs = ["bin.scala"],  # compiled with 3.3 (the default)
+    main_class = "C",
+    deps = [
+        ":lib",  # compiled with 3.3 (default)
+        ":lib211",  # compiled with 2.11 (that target overrides version)
+    ],
+)

examples/crossbuild/2_deps/bin.scala

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+object C extends App {
+  println("Hello, world")
+}

examples/crossbuild/2_deps/lib.scala

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+class A

examples/crossbuild/2_deps/lib_default.scala

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+class B

examples/crossbuild/3_select/BUILD

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+load("@io_bazel_rules_scala//scala:scala.bzl", "scala_binary", "scala_library")
+load("@io_bazel_rules_scala//scala:scala_cross_version_select.bzl", "select_for_scala_version")
+
+# Here we demonstrate how to provide distinct source files depending on the version requested
+
+# Trying to provide library that works with all Scala versions:
+scala_library(
+    name = "lib",
+    srcs = select_for_scala_version(
+        before_3 = [
+            # for Scala version < 3
+            "lib2.scala",
+        ],
+        since_3 = [
+            # for 3 ≤ Scala version
+            "lib3.scala",
+        ],
+    ),
+)
+
+scala_binary(
+    name = "bin2",
+    srcs = ["bin.scala"],
+    main_class = "B",
+    scala_version = "2.13.12",
+    deps = [":lib"],
+)
+
+scala_binary(
+    name = "bin3",
+    srcs = ["bin.scala"],
+    main_class = "B",
+    scala_version = "3.3.1",
+    deps = [":lib"],
+)

examples/crossbuild/3_select/bin.scala

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+object B extends App {
+  (new A).say
+}

examples/crossbuild/3_select/lib2.scala

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+class A {
+  def say = println("Hello 2")
+}

examples/crossbuild/3_select/lib3.scala

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+class A:
+  def say =
+    println("Hello 3")