fix: std.manifestIni requires a sections field, matching official Jsonnet (#799)

sjsonnet/src/sjsonnet/stdlib/ManifestModule.scala

@@ -486,17 +486,22 @@ object ManifestModule extends AbstractFunctionModule {
           case (k, v)             => Seq(k + " = " + render(v))
         }
       }
-      val lines = materialized.obj
+      val mainLines = materialized.obj
         .get("main")
-        .fold(Iterable[String]())(x => sect(x.asInstanceOf[ujson.Obj])) ++
-        materialized.obj
-          .get("sections")
-          .fold(Iterable[String]())(x =>
-            // TODO remove the `toSeq` once this is fixed in scala3
-            x.obj.toSeq.flatMap { case (k, v) =>
-              Seq("[" + k + "]") ++ sect(v.asInstanceOf[ujson.Obj])
-            }
-          )
+        .fold(Iterable[String]())(x => sect(x.asInstanceOf[ujson.Obj]))
+      // Official std.jsonnet accesses `ini.sections` directly, so a missing `sections`
+      // field is an error rather than being silently treated as empty (issue #799).
+      // `main` stays optional, matching `std.objectHas(ini, 'main')` in the upstream impl.
+      val sectionLines = materialized.obj.get("sections") match {
+        case Some(x) =>
+          // TODO remove the `toSeq` once this is fixed in scala3
+          x.obj.toSeq.flatMap { case (k, v) =>
+            Seq("[" + k + "]") ++ sect(v.asInstanceOf[ujson.Obj])
+          }
+        case None =>
+          Error.fail("Field does not exist: sections", pos)(ev)
+      }
+      val lines = mainLines ++ sectionLines
       lines.flatMap(Seq(_, "\n")).mkString
     },
     /**

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

@@ -0,0 +1 @@
+std.manifestIni({ main: { a: '1' } })

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

@@ -0,0 +1,2 @@
+sjsonnet.Error: [std.manifestIni] Field does not exist: sections
+    at [<root>].(error.manifestini_requires_sections.jsonnet:1:16)

sjsonnet/test/resources/new_test_suite/manifestini_sections_required.jsonnet

@@ -0,0 +1,15 @@
+// Issue #799: std.manifestIni follows official Jsonnet — `sections` is required (a missing
+// `sections` field is an error, see error.manifestini_requires_sections), while `main` is optional.
+std.assertEqual(
+  std.manifestIni({ main: { a: '1', b: '2' }, sections: { s: { b: '2' } } }),
+  'a = 1\nb = 2\n[s]\nb = 2\n'
+) &&
+std.assertEqual(
+  std.manifestIni({ sections: { s: { b: '2' } } }),
+  '[s]\nb = 2\n'
+) &&
+std.assertEqual(
+  std.manifestIni({ sections: {} }),
+  ''
+) &&
+true

sjsonnet/test/resources/new_test_suite/manifestini_sections_required.jsonnet.golden

@@ -0,0 +1 @@
+true