fix: bind self/$ to outer self in super[name] lookup (#829)

[He-Pin]

Motivation

Issue #829: sjsonnet failed to evaluate grafana/mimir manifests with

sjsonnet.Error: Field does not exist: ingest_storage_ingester_autoscaling_enabled
    at [overrideSuperIfExists].(mimir/rollout-operator.libsonnet:18:64)
    at [<root>].(mimir/memberlist.libsonnet:106:50)

while google/jsonnet (C++), go-jsonnet, and jrsonnet all evaluate it correctly.

Root cause: visitLookupSuper (computed-key super[name]) called sup.value(key, pos) without passing the actual self, so Val.Obj.value defaulted self to sup (the parent in the merge chain). Fields retrieved through super[name] therefore had their $/self bound to the parent rather than the merged outer self, making _config keys defined in mixins applied after the parent unreachable. The static-key path visitSelectSuper (super.name) was already correct — it passed scope.bindings(e.selfIdx) as self. The two paths must agree.

Modification

sjsonnet/src/sjsonnet/Evaluator.scala — make visitLookupSuper mirror visitSelectSuper by passing the current self explicitly:

   def visitLookupSuper(e: LookupSuper)(implicit scope: ValScope): Val = {
     var sup = scope.bindings(e.selfIdx + 1).asInstanceOf[Val.Obj]
     val key = visitExpr(e.index).cast[Val.Str]
-    if (sup == null) sup = scope.bindings(e.selfIdx).asInstanceOf[Val.Obj]
-    sup.value(key.str, e.pos)
+    val self = scope.bindings(e.selfIdx).asInstanceOf[Val.Obj]
+    if (sup == null) sup = self
+    sup.value(key.str, e.pos, self)
   }

Two regression tests under sjsonnet/test/resources/new_test_suite/ (run on JVM, Scala.js and Scala Native via FileTests):

1. super_lookup_dollar_binding.jsonnet — focused directional suite covering: parity between super.name and super[name] for $ binding; the overrideSuperIfExists pattern verbatim; bare super[name] (no override merge); 3-level chained mixins; computed key from a variable; object-extension syntax obj { f: super[name] }.
2. super_lookup_mimir_pattern.jsonnet — multi-file end-to-end reproduction of the issue, with three .libsonnet files mirroring rollout-operator / memberlist / ingest-storage-ingester-autoscaling. Without the fix, this throws the exact error from the issue.

Result

super[name] now agrees with super.name; fields retrieved via computed-key super lookup see $ bound to the outermost merge result, matching google/jsonnet, go-jsonnet, and jrsonnet. Verified by reverting the one-line fix locally — both regression tests fail with the original "Field does not exist" message and the entry-mimir.jsonnet evaluation in the issue is unblocked.

Test plan:

• ./mill 'sjsonnet.jvm[3.3.7]'.test — 5/5 passing
• ./mill 'sjsonnet.jvm[2.13.18]'.test — 4/4 passing
• ./mill 'sjsonnet.jvm[2.12.21]'.test — 4/4 passing
• ./mill 'sjsonnet.js[3.3.7]'.test — 407/407 passing
• ./mill 'sjsonnet.native[3.3.7]'.test — 428/428 passing
• ./mill __.checkFormat — clean
• Cross-checked output against jsonnet (C++ v0.22.0) on minimal repros and both new test files

References

• Fixes Scala fails to evaluate mimir manifests #829
• Reporter test fixtures: https://github.com/CertainLach/jrsonnet/blob/master/tests/realworld/entry-mimir.jsonnet , https://github.com/CertainLach/jrsonnet/blob/master/tests/realworld/jsonnetfile.json
• Upstream overrideSuperIfExists definition: https://github.com/grafana/mimir/blob/39dd4ffb859d0abb3951d406495bc4bd422600dd/operations/mimir/memberlist.libsonnet#L171