fix #32465, inference of splatting unionall NamedTuple types (#32494)

(cherry picked from commit 2350c04)

base/compiler/abstractinterpretation.jl

@@ -422,10 +422,13 @@ function precise_container_type(@nospecialize(typ), vtypes::VarTable, sv::Infere
     tti0 = widenconst(typ)
     tti = unwrap_unionall(tti0)
     if isa(tti, DataType) && tti.name === NamedTuple_typename
-        tti0 = tti.parameters[2]
-        while isa(tti0, TypeVar)
-            tti0 = tti0.ub
+        # A NamedTuple iteration is the the same as the iteration of its Tuple parameter:
+        # compute a new `tti == unwrap_unionall(tti0)` based on that Tuple type
+        tti = tti.parameters[2]
+        while isa(tti, TypeVar)
+            tti = tti.ub
         end
+        tti0 = rewrap_unionall(tti, tti0)
     end
     if isa(tti, Union)
         utis = uniontypes(tti)

test/compiler/inference.jl

@@ -1928,6 +1928,12 @@ Base.iterate(::Iterator27434, ::Any) = nothing
 @test @inferred((1, 2, 3) == (1, 2, 3))
 @test Core.Compiler.return_type(splat27434, Tuple{typeof(Iterators.repeated(1))}) == Union{}
 
+# issue #32465
+let rt = Base.return_types(splat27434, (NamedTuple{(:x,), Tuple{T}} where T,))
+    @test rt == Any[Tuple{Any}]
+    @test !Base.has_free_typevars(rt[1])
+end
+
 # issue #27078
 f27078(T::Type{S}) where {S} = isa(T, UnionAll) ? f27078(T.body) : T
 T27078 = Vector{Vector{T}} where T