Fix crash in map_lifting.rs

[umanwizard]

Motivation

Fixes #8713

Tips for reviewer

Some true elements have already been popped from the_same (line 128), so this could panic before.

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered.
• This PR adds a release note for any
  user-facing behavior changes.

[asenac]

Thanks for fixing this. It seems I introduced this crash under #6520.

I'd add a unit tests for this like the following:

diff --git a/src/transform/tests/testdata/lifting b/src/transform/tests/testdata/lifting
index 6694bf3b4..a0ca96417 100644
--- a/src/transform/tests/testdata/lifting
+++ b/src/transform/tests/testdata/lifting
@@ -368,3 +368,20 @@ opt
 | Union %1 %2
 ----
 ----
+
+build format=types apply=LiteralLifting
+(constant [[1 2 3] [1 4 3]] ([int64 int64 int64] [[1 2]]))
+----
+%0 =
+| Constant (2) (4)
+| | types = (Int64?)
+| | keys = ((#0))
+| Map 1
+| | types = (Int64?, Int64)
+| | keys = ((#0))
+| Project (#1, #0)
+| | types = (Int64, Int64?)
+| | keys = ((#1))
+| Map 3
+| | types = (Int64, Int64?, Int64)
+| | keys = ((#1))

[umanwizard]

OK, thanks for letting me know about those data-driven tests @asenac . I've added the one you suggested.

[philip-stoev]

As discussed with @umanwizard I am going to re-test this once all the 3 PRs have collectively landed in "main". So hitting "Approve" here.