From b23811e1a030073de8b5a745965f37bb3a55ab6f Mon Sep 17 00:00:00 2001
From: Shuhei Kadowaki <40514306+aviatesk@users.noreply.github.com>
Date: Tue, 22 Oct 2024 05:23:04 +0900
Subject: [PATCH] inference: fix inference error from constructing invalid
 `TypeVar` (#56264)

- fixes JuliaLang/julia#56248

(cherry picked from commit 08d11d041b22fe90380e56be4fb4d44aaf46ec85)
---
 base/compiler/tfuncs.jl    | 12 ++++++++++--
 test/compiler/inference.jl |  8 ++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/base/compiler/tfuncs.jl b/base/compiler/tfuncs.jl
index 7c5503d2e6068e..e2773752c68e6b 100644
--- a/base/compiler/tfuncs.jl
+++ b/base/compiler/tfuncs.jl
@@ -574,8 +574,16 @@ add_tfunc(svec, 0, INT_INF, @nospecs((𝕃::AbstractLattice, args...)->SimpleVec
                 return TypeVar
             end
         end
-        tv = TypeVar(nval, lb, ub)
-        return PartialTypeVar(tv, lb_certain, ub_certain)
+        lb_valid = lb isa Type || lb isa TypeVar
+        ub_valid = ub isa Type || ub isa TypeVar
+        if lb_valid && ub_valid
+            tv = TypeVar(nval, lb, ub)
+            return PartialTypeVar(tv, lb_certain, ub_certain)
+        elseif !lb_valid && lb_certain
+            return Union{}
+        elseif !ub_valid && ub_certain
+            return Union{}
+        end
     end
     return TypeVar
 end
diff --git a/test/compiler/inference.jl b/test/compiler/inference.jl
index 6f4aabddbedf88..270622c2332a26 100644
--- a/test/compiler/inference.jl
+++ b/test/compiler/inference.jl
@@ -5164,3 +5164,11 @@ end
 
 issue55882_nfields(x::Union{T,Nothing}) where T<:Number = nfields(x)
 @test only(Base.return_types(issue55882_nfields)) <: Int
+
+# JuliaLang/julia#56248
+@test Base.infer_return_type() do
+    TypeVar(:Issue56248, 1)
+end === Union{}
+@test Base.infer_return_type() do
+    TypeVar(:Issue56248, Any, 1)
+end === Union{}