Add a few cross-build examples (#1587)

* Set up example

* A few examples

---------

Co-authored-by: mkuta <[email protected]>

Author: aszady

examples/crossbuild/1_single/BUILD

@@ -0,0 +1,25 @@
+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

@@ -0,0 +1,3 @@
+object C extends App {
+  println("Hello")
+}

examples/crossbuild/1_single/lib.scala

@@ -0,0 +1 @@
+class A

examples/crossbuild/1_single/test.scala

@@ -0,0 +1,7 @@
+import org.scalatest.flatspec.AnyFlatSpec
+
+class Zero extends AnyFlatSpec {
+  "Equality" should "be tested" in {
+    assert (0 == -0)
+  }
+}

examples/crossbuild/2_deps/BUILD

@@ -0,0 +1,37 @@
+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

@@ -0,0 +1,3 @@
+object C extends App {
+  println("Hello, world")
+}

examples/crossbuild/2_deps/lib.scala

@@ -0,0 +1 @@
+class A

examples/crossbuild/2_deps/lib_default.scala

@@ -0,0 +1 @@
+class B

examples/crossbuild/3_select/BUILD

@@ -0,0 +1,35 @@
+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

@@ -0,0 +1,3 @@
+object B extends App {
+  (new A).say
+}

examples/crossbuild/3_select/lib2.scala

@@ -0,0 +1,3 @@
+class A {
+  def say = println("Hello 2")
+}

examples/crossbuild/3_select/lib3.scala

@@ -0,0 +1,3 @@
+class A:
+  def say =
+    println("Hello 3")

examples/crossbuild/WORKSPACE

@@ -0,0 +1,54 @@
+workspace(name = "cross_build")
+
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "bazel_skylib",
+    sha256 = "d00f1389ee20b60018e92644e0948e16e350a7707219e7a390fb0a99b6ec9262",
+    urls = [
+        "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.7.0/bazel-skylib-1.7.0.tar.gz",
+        "https://github.com/bazelbuild/bazel-skylib/releases/download/1.7.0/bazel-skylib-1.7.0.tar.gz",
+    ],
+)
+
+local_repository(
+    name = "io_bazel_rules_scala",
+    path = "../..",
+)
+
+load("@io_bazel_rules_scala//:scala_config.bzl", "scala_config")
+
+scala_config(
+    scala_version = "3.3.1",
+    scala_versions = [
+        "2.11.12",
+        "2.13.12",
+        "3.3.1",
+    ],
+)
+
+load(
+    "@io_bazel_rules_scala//scala:scala.bzl",
+    "rules_scala_setup",
+    "rules_scala_toolchain_deps_repositories",
+)
+
+rules_scala_setup()
+
+rules_scala_toolchain_deps_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()
+
+load("@io_bazel_rules_scala//testing:scalatest.bzl", "scalatest_repositories", "scalatest_toolchain")
+
+scalatest_repositories()
+
+scalatest_toolchain()

test/shell/test_examples.sh

@@ -51,10 +51,15 @@ function semanticdb_example() {
   test_example examples/semanticdb build_semanticdb_example
 }
 
+function cross_build_example() {
+  test_example examples/crossbuild "bazel build //..."
+}
+
 $runner scalatest_repositories_example
 $runner specs2_junit_repositories_example
 $runner multi_framework_toolchain_example
 $runner semanticdb_example
 $runner scala3_1_example
 $runner scala3_2_example
-$runner scala3_3_example
+$runner scala3_3_example
+$runner cross_build_example