From 109a43fd53953c5e28fc055f9ea46d3877356897 Mon Sep 17 00:00:00 2001
From: Jameson Nash <vtjnash@gmail.com>
Date: Mon, 15 Aug 2016 22:51:55 -0400
Subject: [PATCH] fix "improved" correctness of fieldtype

the getfield_tfunc was missing a test for whether
the fields were all equivalent before concluding
that the result type was exact

fixes the fix #17953
fix #18037

(cherry picked from commit 06a8d891e71c12a7598b2fa818dcfc29437d5c0b)
ref #18045
---
 base/inference.jl |  9 +++++----
 test/inference.jl | 15 +++++++++++++++
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/base/inference.jl b/base/inference.jl
index 869b30aa0f3e2..95471df20d788 100644
--- a/base/inference.jl
+++ b/base/inference.jl
@@ -478,7 +478,7 @@ function getfield_tfunc(s0::ANY, name)
                     # in the current type system
                     typ = limit_type_depth(R, 0, true,
                                            filter!(x->isa(x,TypeVar), Any[s.parameters...]))
-                    return typ, isleaftype(s) && typeseq(typ, R)
+                    return typ, isleaftype(s) && isa(R, Type) && typeof(R) === typeof(typ) && typeseq(R, typ)
                 end
             end
         end
@@ -501,14 +501,15 @@ function getfield_tfunc(s0::ANY, name)
     elseif length(s.types) == 1 && isempty(s.parameters)
         return s.types[1], true
     else
-        R = reduce(tmerge, Bottom, map(unwrapva,s.types)) #=Union{s.types...}=#
+        R = reduce(tmerge, Bottom, map(unwrapva, s.types)) #=Union{s.types...}=#
+        alleq = isa(R, Type) && typeof(R) === typeof(s.types[1]) && typeseq(R, s.types[1])
         # do the same limiting as the known-symbol case to preserve type-monotonicity
         if isempty(s.parameters)
-            return R, typeseq(R, s.types[1])
+            return R, alleq
         else
             typ = limit_type_depth(R, 0, true,
                                    filter!(x->isa(x,TypeVar), Any[s.parameters...]))
-            return typ, isleaftype(s) && typeseq(typ, R)
+            return typ, alleq && isleaftype(s) && typeof(R) === typeof(typ) && typeseq(R, typ)
         end
     end
 end
diff --git a/test/inference.jl b/test/inference.jl
index f1f4fbb9b1457..a324716b2511b 100644
--- a/test/inference.jl
+++ b/test/inference.jl
@@ -307,6 +307,21 @@ let T = Array{Tuple{Vararg{Float64,TypeVar(:dim)}},1},
 end
 @test f16530a(:d) == Vector
 
+let T1 = Tuple{Int, Float64},
+    T2 = Tuple{Int, Float32},
+    T = Tuple{T1, T2}
+
+    global f18037
+    f18037() = fieldtype(T, 1)
+    f18037(i) = fieldtype(T, i)
+
+    @test f18037() === T1
+    @test f18037(1) === T1
+    @test f18037(2) === T2
+
+    @test Base.return_types(f18037, ()) == Any[Type{T1}]
+    @test Base.return_types(f18037, (Int,)) == Any[Type{TypeVar(:T, Tuple{Int, AbstractFloat})}]
+end
 
 # issue #18015
 type Triple18015