From b0de4c629d9cf0cf0e755990d34bc64c8a96abf3 Mon Sep 17 00:00:00 2001
From: Jeff Bezanson <jeff.bezanson@gmail.com>
Date: Fri, 28 Sep 2018 13:43:39 -0400
Subject: [PATCH] fix #20872, handle UnionAll types in `which`

---
 base/reflection.jl | 10 +++++++---
 test/reflection.jl |  8 ++++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/base/reflection.jl b/base/reflection.jl
index da407a73c82eb..066125fda10a9 100644
--- a/base/reflection.jl
+++ b/base/reflection.jl
@@ -647,7 +647,7 @@ function to_tuple_type(@nospecialize(t))
         t = Tuple{t...}
     end
     if isa(t,Type) && t<:Tuple
-        for p in t.parameters
+        for p in unwrap_unionall(t).parameters
             if !(isa(p,Type) || isa(p,TypeVar))
                 error("argument tuple type must contain only types")
             end
@@ -660,8 +660,12 @@ end
 
 function signature_type(@nospecialize(f), @nospecialize(args))
     f_type = isa(f, Type) ? Type{f} : typeof(f)
-    arg_types = isa(args, Type) ? args.parameters : args
-    return Tuple{f_type, arg_types...}
+    if isa(args, Type)
+        u = unwrap_unionall(args)
+        return rewrap_unionall(Tuple{f_type, u.parameters...}, args)
+    else
+        return Tuple{f_type, args...}
+    end
 end
 
 """
diff --git a/test/reflection.jl b/test/reflection.jl
index b1f5fecc9178f..db85f100af910 100644
--- a/test/reflection.jl
+++ b/test/reflection.jl
@@ -797,3 +797,11 @@ end
 @test !(:Test in names(M26267, all=true, imported=false))
 @test :Test in names(M26267, all=true, imported=true)
 @test :Test in names(M26267, all=false, imported=true)
+
+# issue #20872
+f20872(::Val{N}, ::Val{N}) where {N} = true
+f20872(::Val, ::Val) = false
+@test which(f20872, Tuple{Val{N},Val{N}} where N).sig == Tuple{typeof(f20872), Val{N}, Val{N}} where N
+@test which(f20872, Tuple{Val,Val}).sig == Tuple{typeof(f20872), Val, Val}
+@test which(f20872, Tuple{Val,Val{N}} where N).sig == Tuple{typeof(f20872), Val, Val}
+@test_throws ErrorException which(f20872, Tuple{Any,Val{N}} where N)