fix: align std.lines with official semantics

sjsonnet/src/sjsonnet/stdlib/ManifestModule.scala

@@ -347,25 +347,14 @@ object ManifestModule extends AbstractFunctionModule {
    */
   private object Lines extends Val.Builtin1("lines", "arr") {
     def evalRhs(v1: Eval, ev: EvalScope, pos: Position): Val = {
+      val out = new StringBuilder
       v1.value.asArr.foreach {
-        case _: Val.Str | _: Val.Null => // donothing
-        case x                        =>
+        case s: Val.Str  => out.append(s.str).append('\n')
+        case _: Val.Null => // skip nulls like std.join
+        case x           =>
           Error.fail("std.lines: expected string or null element, got " + x.value.prettyName)
       }
-      Val.Str(
-        pos,
-        Materializer
-          .apply(v1.value)(ev)
-          .asInstanceOf[ujson.Arr]
-          .value
-          .filter(_ != ujson.Null)
-          .map {
-            case ujson.Str(s) => s + "\n"
-            case _            =>
-              throw new RuntimeException("Unexpected") /* we ensure it's all strings above */
-          }
-          .mkString
-      )
+      Val.Str(pos, out.toString)
     }
   }
 

sjsonnet/test/resources/new_test_suite/error.std_lines_string.jsonnet

@@ -0,0 +1 @@
+std.lines("a\nb\n")

sjsonnet/test/resources/new_test_suite/error.std_lines_string.jsonnet.golden

@@ -0,0 +1,2 @@
+sjsonnet.Error: [std.lines] Wrong parameter type: expected Array, got string
+    at [<root>].(error.std_lines_string.jsonnet:1:10)

sjsonnet/test/src/sjsonnet/StdLibOfficialCompatibilityTests.scala

@@ -15,6 +15,15 @@ object StdLibOfficialCompatibilityTests extends TestSuite {
       assert(evalErr("""std.flattenArrays([[1], null, [2]])""").contains("array and null"))
     }
 
+    test("lines follows official array-to-text semantics") {
+      eval("""std.lines(["a", "b"])""") ==> ujson.Str("a\nb\n")
+      eval("""std.lines(["a", null, "b"])""") ==> ujson.Str("a\nb\n")
+
+      val stringInputError = evalErr("""std.lines("a\nb\n")""")
+      assert(stringInputError.contains("expected Array"))
+      assert(stringInputError.contains("got string"))
+    }
+
     test("flattenDeepArray wraps scalar values") {
       eval("""std.flattenDeepArray(1)""") ==> ujson.Arr(1)
       eval("""std.flattenDeepArray(null)""") ==> ujson.Arr(ujson.Null)