fix a case where Vararg.T might be accessed when undefined (#41867)

Author: JeffBezanson

base/compiler/typelimits.jl

@@ -130,7 +130,7 @@ function _limit_type_size(@nospecialize(t), @nospecialize(c), sources::SimpleVec
     elseif isa(t, DataType)
         if isa(c, Core.TypeofVararg)
             # Tuple{Vararg{T}} --> Tuple{T} is OK
-            return _limit_type_size(t, c.T, sources, depth, 0)
+            return _limit_type_size(t, unwrapva(c), sources, depth, 0)
         elseif isType(t) # allow taking typeof as Type{...}, but ensure it doesn't start nesting
             tt = unwrap_unionall(t.parameters[1])
             (!isa(tt, DataType) || isType(tt)) && (depth += 1)

test/compiler/inference.jl

@@ -44,6 +44,11 @@ let t = Tuple{Ref{T},T,T} where T, c = Tuple{Ref, T, T} where T # #36407
     @test t <: Core.Compiler.limit_type_size(t, c, Union{}, 1, 100)
 end
 
+# obtain Vararg with 2 undefined fields
+let va = ccall(:jl_type_intersection_with_env, Any, (Any, Any), Tuple{Tuple}, Tuple{Tuple{Vararg{Any, N}}} where N)[2][1]
+    @test Core.Compiler.limit_type_size(Tuple, va, Union{}, 2, 2) === Any
+end
+
 let # 40336
     t = Type{Type{Int}}
     c = Type{Int}