From 17170a6736a01d0f4a59fde2cad34a12c2fa7409 Mon Sep 17 00:00:00 2001
From: Colin Caine <cmcaine@gmail.com>
Date: Mon, 8 Feb 2021 20:30:22 +0000
Subject: [PATCH] Add `Base.isdone(itr::EachLine, state...)` (#39562)

With this method, `isempty` won't consume values from the iterator (See #27412).
---
 base/io.jl   | 2 ++
 test/read.jl | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/base/io.jl b/base/io.jl
index eb9eff598f712..e15551cfbdfa7 100644
--- a/base/io.jl
+++ b/base/io.jl
@@ -1023,6 +1023,8 @@ eltype(::Type{<:EachLine}) = String
 
 IteratorSize(::Type{<:EachLine}) = SizeUnknown()
 
+isdone(itr::EachLine, state...) = eof(itr.stream)
+
 struct ReadEachIterator{T, IOT <: IO}
     stream::IOT
 end
diff --git a/test/read.jl b/test/read.jl
index b63658d225111..b7e8c2260a4f9 100644
--- a/test/read.jl
+++ b/test/read.jl
@@ -617,3 +617,12 @@ let p = Pipe()
     wait(t)
     close(p)
 end
+
+@testset "issue #27412" begin
+    itr = eachline(IOBuffer("a"))
+    @test !isempty(itr)
+    # check that the earlier isempty did not consume the iterator
+    @test !isempty(itr)
+    first(itr) # consume the iterator
+    @test  isempty(itr) # now it is empty
+end