From 44855863aa5be116e22d59fe5f64a121aaadbe57 Mon Sep 17 00:00:00 2001
From: KristofferC <kcarlsson89@gmail.com>
Date: Mon, 18 Oct 2021 09:32:35 +0200
Subject: [PATCH] revert isequal inference improvement (#40594) to fix #42457

---
 base/tuple.jl | 12 ++++--------
 test/tuple.jl |  8 ++++++++
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/base/tuple.jl b/base/tuple.jl
index b45e1efc91413..28be1338a5cb1 100644
--- a/base/tuple.jl
+++ b/base/tuple.jl
@@ -380,14 +380,10 @@ filter(f, t::Tuple) = length(t) < 32 ? filter_rec(f, t) : Tuple(filter(f, collec
 
 ## comparison ##
 
-isequal(t1::Tuple, t2::Tuple) = length(t1) == length(t2) && _isequal(t1, t2)
-_isequal(::Tuple{}, ::Tuple{}) = true
-function _isequal(t1::Tuple{Any,Vararg{Any,N}}, t2::Tuple{Any,Vararg{Any,N}}) where {N}
-    isequal(t1[1], t2[1]) || return false
-    t1, t2 = tail(t1), tail(t2)
-    # avoid dynamic dispatch by telling the compiler relational invariants
-    return isa(t1, Tuple{}) ? true : _isequal(t1, t2::Tuple{Any,Vararg{Any}})
-end
+isequal(t1::Tuple, t2::Tuple) = (length(t1) == length(t2)) && _isequal(t1, t2)
+_isequal(t1::Tuple{}, t2::Tuple{}) = true
+_isequal(t1::Tuple{Any}, t2::Tuple{Any}) = isequal(t1[1], t2[1])
+_isequal(t1::Tuple, t2::Tuple) = isequal(t1[1], t2[1]) && _isequal(tail(t1), tail(t2))
 function _isequal(t1::Any32, t2::Any32)
     for i = 1:length(t1)
         if !isequal(t1[i], t2[i])
diff --git a/test/tuple.jl b/test/tuple.jl
index b5f8477130d03..acd542d883241 100644
--- a/test/tuple.jl
+++ b/test/tuple.jl
@@ -671,3 +671,11 @@ end
 
 # https://github.com/JuliaLang/julia/issues/40814
 @test Base.return_types(NTuple{3,Int}, (Vector{Int},)) == Any[NTuple{3,Int}]
+
+@testset "inference through isequal #42457" begin
+    function fluffs(a::Tuple{Int,Int,Int}, b::Tuple)::Bool
+        return Base.isequal(a, Base.inferencebarrier(b)::Tuple)
+    end
+
+    @test fluffs((1, 1, 1), (1, 1, 1))
+end