chore: Make std.setUnion accept str. (#480)

Motivation:
Make std.setUnion accept str.

Author: He-Pin

build.mill

@@ -203,7 +203,8 @@ object sjsonnet extends VersionFileModule {
 
     val osName = System.getProperty("os.name").toLowerCase
 
-    def nativeLinkingOptions = super.nativeLinkingOptions() ++ (if (osName == "linux") Seq("-static") else Seq())
+    def nativeLinkingOptions =
+      super.nativeLinkingOptions() ++ (if (osName == "linux") Seq("-static") else Seq())
 
     def releaseMode = ReleaseMode.ReleaseFull
     def nativeLTO = LTO.Full

sjsonnet/src/sjsonnet/Std.scala

@@ -1707,8 +1707,8 @@ class Std(
     builtin(Set_),
     builtinWithDefaults("setUnion", "a" -> null, "b" -> null, "keyF" -> Val.False(dummyPos)) {
       (args, pos, ev) =>
-        val a = toSetArr(args, 0, pos, ev)
-        val b = toSetArr(args, 1, pos, ev)
+        val a = toArrOrString(args(0), pos, ev)
+        val b = toArrOrString(args(1), pos, ev)
         if (a.isEmpty) {
           uniqArr(pos, ev, sortArr(pos, ev, args(1), args(2)), args(2))
         } else if (b.isEmpty) {
@@ -1948,13 +1948,6 @@ class Std(
     builtin(Native)
   )
 
-  private def toSetArr(args: Array[Val], idx: Int, pos: Position, ev: EvalScope) = {
-    args(idx) match {
-      case arr: Val.Arr => arr.asLazyArray
-      case _            => Error.fail(f"Argument $idx must be an array", pos)(ev)
-    }
-  }
-
   private def toArrOrString(arg: Val, pos: Position, ev: EvalScope) = {
     arg match {
       case arr: Val.Arr => arr.asLazyArray

sjsonnet/test/src/sjsonnet/StdSetUnionTests.scala

@@ -0,0 +1,18 @@
+package sjsonnet
+
+import sjsonnet.TestUtils.eval
+import utest.*
+
+object StdSetUnionTests extends TestSuite {
+
+  def tests: Tests = Tests {
+    test {
+      eval("""
+          |{
+          |  local options = ['a', 'b', 'c'],
+          |  union: std.setUnion('d', options),
+          |}
+          |""".stripMargin).toString ==> """{"union":["a","b","c","d"]}"""
+    }
+  }
+}