fixes #25908; resolves lent enum disambiguation (#25929)

fixes #25908

When an enum identifier is resolved as an `nkSymChoice`, one of the
candidates may come from a loop-local view and carry `tyVar` or
`tyLent`.

Enum disambiguation should compare the underlying enum type only.
Otherwise a pure-enum field can win incorrectly even though the intended
symbol is already present in the choice set.

Keep the `includePureEnum` lookup path for enum-typed expectations so
#23976 still works, but normalize `var`/`lent` only at the symchoice
selection point.

compiler/sem.nim

@@ -105,9 +105,12 @@ proc fitNode(c: PContext, formal: PType, arg: PNode; info: TLineInfo): PNode =
     result.typ = formal
   elif arg.kind in nkSymChoices and formal.skipTypes(abstractInst).kind == tyEnum:
     # Pick the right 'sym' from the sym choice by looking at 'formal' type:
+    # The choice candidates may be wrapped in `var`/`lent` when they come from
+    # a loop-local view, but for enum disambiguation only the underlying enum
+    # type matters.
     result = nil
     for ch in arg:
-      if sameType(ch.typ, formal):
+      if sameType(ch.typ.skipTypes({tyVar, tyLent}), formal):
         return ch
     typeMismatch(c.config, info, formal, arg.typ, arg)
   else:

testament/important_packages.nim

@@ -158,6 +158,7 @@ pkg "sim"
 pkg "smtp", "nimble compileExample"
 pkg "snip", "nimble test", "https://github.com/genotrance/snip"
 pkg "ssostrings", "nim c -r tests/tssostrings.nim"
+pkg "ssz_serialization", "nim c -r tests/test_all.nim"
 pkg "stew"
 pkg "stint", "nimble test_internal"
 pkg "strslice"

tests/enum/tenum.nim

@@ -283,3 +283,13 @@ block: # bug #23952
       doAssert s1 != s2
     static: foo()
     foo()
+
+# bug #25908
+type S {.pure.} = enum a, b
+
+iterator foo(x: array[1, S]): lent S =
+  yield x[0]
+
+iterator f(_: int | int): S =
+  for a in foo([S.b]): yield a
+for v in f(0): doAssert v == S.b