Add examples/overridden_artifacts and test

Adds the `examples/overridden_artifacts` repository and the
corresponding `overridden_artifacts_example` test case in
`test/shell/test_examples.sh`. Broken out from bazelbuild#1710, and part of bazelbuild#1482
and bazelbuild#1652.

@dmivankov noticed the design bug in the upcoming Bzlmod API for
`overridden_artifacts` that this change addresses. See:

- bazelbuild#1482 (comment)
- bazelbuild#1482 (comment)

Makes `_validate_scalac_srcjar()` and `dt_patched_compiler_setup()` in
`scala/private/macros/scala_repositories.bzl` more tolerant of
dictionaries containing keys mapped to `None`. The new
`overridden_artifacts_example` test covers this.

Sets `.bazelversion` in the new repo to 7.5.0 to match changes in
both bazelbuild#1710 and bazelbuild#1711.

This change is smaller and more focused than bazelbuild#1710, and should
ultimately make that pull request smaller and/or easier to review.

examples/overridden_artifacts/.bazelrc

@@ -0,0 +1 @@
+import ../../.bazelrc

examples/overridden_artifacts/.bazelversion

@@ -0,0 +1 @@
+7.5.0

examples/overridden_artifacts/BUILD

@@ -0,0 +1,12 @@
+load("@rules_scala//scala:scala.bzl", "scala_library", "scala_test")
+
+scala_library(
+    name = "hello",
+    srcs = ["Hello.scala"],
+)
+
+scala_test(
+    name = "hello-test",
+    srcs = ["HelloTest.scala"],
+    deps = [":hello"],
+)

examples/overridden_artifacts/Hello.scala

@@ -0,0 +1,4 @@
+package overriddenartifactstest
+
+class Hello(version: String):
+  def greetings(): String = "Hello, World! This is Scala " + version + "."

examples/overridden_artifacts/HelloTest.scala

@@ -0,0 +1,12 @@
+package overriddenartifactstest
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class HelloTest extends AnyFunSuite:
+  test("greetings includes the correct Scala version number") {
+    val hello = new Hello(util.Properties.versionNumberString)
+
+    // Apparently Scala 3 code will still return a Scala 2 version number:
+    // - https://users.scala-lang.org/t/what-scala-library-version-is-used-by-which-scala-3-version/9999
+    assert(hello.greetings().endsWith("2.13.14."))
+  }

examples/overridden_artifacts/WORKSPACE

@@ -0,0 +1,98 @@
+workspace(name = "overridden_artifacts")
+
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+local_repository(
+    name = "rules_scala",
+    path = "../..",
+)
+
+load("@rules_scala//scala:deps.bzl", "rules_scala_dependencies")
+
+rules_scala_dependencies()
+
+load(
+    "@rules_java//java:repositories.bzl",
+    "rules_java_dependencies",
+    "rules_java_toolchains",
+)
+
+rules_java_dependencies()
+
+load("@bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")
+
+bazel_skylib_workspace()
+
+http_archive(
+    name = "rules_python",
+    sha256 = "ca2671529884e3ecb5b79d6a5608c7373a82078c3553b1fa53206e6b9dddab34",
+    strip_prefix = "rules_python-0.38.0",
+    url = "https://github.com/bazelbuild/rules_python/releases/download/0.38.0/rules_python-0.38.0.tar.gz",
+)
+
+load("@rules_python//python:repositories.bzl", "py_repositories")
+
+py_repositories()
+
+load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps")
+
+protobuf_deps()
+
+rules_java_toolchains()
+
+load("@rules_proto//proto:repositories.bzl", "rules_proto_dependencies")
+
+rules_proto_dependencies()
+
+load("@rules_proto//proto:setup.bzl", "rules_proto_setup")
+
+rules_proto_setup()
+
+load("@rules_proto//proto:toolchains.bzl", "rules_proto_toolchains")
+
+rules_proto_toolchains()
+
+load("@rules_scala//:scala_config.bzl", "scala_config")
+
+scala_config(scala_version = "3.3.5")
+
+load(
+    "@rules_scala//scala:toolchains.bzl",
+    "scala_register_toolchains",
+    "scala_toolchains",
+)
+
+scala_toolchains(
+    # Deliberately set for Scala 3.3 and 2.13 versions less than the most
+    # recently supported. See the `scala_version` setting at the top of
+    # `third_party/repositories/scala_{2_13,3_3}.bzl`.
+    overridden_artifacts = {
+        "io_bazel_rules_scala_scala_library": {
+            "artifact": "org.scala-lang:scala3-library_3:3.3.4",
+            "sha256": "d95184acfcd814da2e051378e4962c653f4b468f4086452ab427af030482bd3c",
+        },
+        "io_bazel_rules_scala_scala_compiler": {
+            "artifact": "org.scala-lang:scala3-compiler_3:3.3.4",
+            "sha256": "2cca65fdb92e2cc393786cae61b4f7bcb9032ad4be61f9cebae1dca72997e52f",
+            # These are _not_ strictly required in this case, but we want to
+            # test that nothing breaks when they're specified.
+            "deps": [
+                "@io_bazel_rules_scala_scala_asm",
+                "@io_bazel_rules_scala_scala_interfaces",
+                "@io_bazel_rules_scala_scala_library",
+                "@io_bazel_rules_scala_scala_tasty_core",
+                "@org_jline_jline_reader",
+                "@org_jline_jline_terminal",
+                "@org_jline_jline_terminal_jni",
+                "@org_scala_sbt_compiler_interface",
+            ],
+        },
+        "io_bazel_rules_scala_scala_library_2": {
+            "artifact": "org.scala-lang:scala-library:2.13.14",
+            "sha256": "43e0ca1583df1966eaf02f0fbddcfb3784b995dd06bfc907209347758ce4b7e3",
+        },
+    },
+    scalatest = True,
+)
+
+scala_register_toolchains()

scala/private/macros/scala_repositories.bzl

@@ -56,7 +56,7 @@ def _validate_scalac_srcjar(srcjar):
     oneof = ["url", "urls", "label"]
     count = 0
     for key in oneof:
-        if key in srcjar:
+        if srcjar.get(key):
             count += 1
     return count == 1
 
@@ -94,7 +94,7 @@ def dt_patched_compiler_setup(scala_version, scala_compiler_srcjar = None):
         ("scala_compiler_srcjar invalid, must be a dict with exactly one of \"label\", \"url\"" +
          " or \"urls\" keys, got: ") + repr(srcjar),
     )
-    if "label" in srcjar:
+    if srcjar.get("label"):
         dt_patched_compiler(
             name = "scala_compiler_source" + version_suffix(scala_version),
             build_file_content = build_file_content,

test/shell/test_examples.sh

@@ -67,6 +67,11 @@ function cross_build_example() {
   test_example examples/crossbuild "bazel build //..."
 }
 
+function overridden_artifacts_example() {
+  test_example examples/overridden_artifacts \
+    "bazel test --test_output=errors //..."
+}
+
 $runner scalatest_repositories_example
 $runner specs2_junit_repositories_example
 $runner multi_framework_toolchain_example
@@ -77,4 +82,5 @@ $runner scala3_3_example
 $runner scala3_4_example
 $runner scala3_5_example
 $runner scala3_6_example
-$runner cross_build_example
+$runner cross_build_example
+$runner overridden_artifacts_example