From ed3a11557761571bceb6fca415d74d2e0e43c898 Mon Sep 17 00:00:00 2001
From: Adam Beckmeyer <adam_gpg@thebeckmeyers.xyz>
Date: Thu, 19 Mar 2020 16:34:01 -0400
Subject: [PATCH 1/2] Show full stacktrace when Channel Task throws

This reuses the machinery that gives good stacktraces when a user
calls wait on a Task. Since bind internally uses _wait2, this
machinery is bypassed currently.

Currently, julia throws an uninformative stacktrace in this situation:

julia> c = Channel(_ -> error("foo"))
Channel{Any}(sz_max:0,sz_curr:0)

julia> for i in c end
ERROR: foo
Stacktrace:
 [1] iterate(::Channel{Any}) at ./channels.jl:459
 [2] top-level scope at ./REPL[2]:1

With this change, the stacktrace is much more informative:

julia> for i in c end
ERROR: TaskFailedException:
foo
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] (::var"#1#2")(::Channel{Any}) at ./REPL[4]:1
 [3] (::Base.var"#652#653"{var"#1#2",Channel{Any}})() at ./channels.jl:129
Stacktrace:
 [1] check_channel_state at ./channels.jl:167 [inlined]
 [2] take_unbuffered(::Channel{Any}) at ./channels.jl:405
 [3] take! at ./channels.jl:383 [inlined]
 [4] iterate(::Channel{Any}, ::Nothing) at ./channels.jl:449
 [5] iterate(::Channel{Any}) at ./channels.jl:448
 [6] top-level scope at ./REPL[5]:1
---
 base/channels.jl |  2 +-
 test/channels.jl | 18 ++++++++++--------
 test/file.jl     |  2 +-
 test/worlds.jl   |  2 +-
 4 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/base/channels.jl b/base/channels.jl
index 82d77b81a3325..8eabcc546edc3 100644
--- a/base/channels.jl
+++ b/base/channels.jl
@@ -281,7 +281,7 @@ function close_chnl_on_taskdone(t::Task, c::Channel)
         if istaskfailed(t)
             excp = task_result(t)
             if excp isa Exception
-                close(c, excp)
+                close(c, TaskFailedException(t))
                 return
             end
         end
diff --git a/test/channels.jl b/test/channels.jl
index 9dc0b3165b3bd..fa7846e9002a2 100644
--- a/test/channels.jl
+++ b/test/channels.jl
@@ -143,8 +143,9 @@ using Distributed
 
     # Error exception in task
     c = Channel(N)
-    bind(c, @async (GC.gc(); yield(); error("foo")))
-    @test_throws ErrorException take!(c)
+    task = @async (GC.gc(); yield(); error("foo"))
+    bind(c, task)
+    @test_throws TaskFailedException(task) take!(c)
     @test !isopen(c)
 
     # Multiple channels closed by the same bound task
@@ -170,10 +171,11 @@ using Distributed
         while isopen(cs[i])
             yield()
         end
-        @test_throws ErrorException wait(cs[i])
-        @test_throws ErrorException take!(cs[i])
-        @test_throws ErrorException put!(cs[i], 1)
-        @test_throws ErrorException fetch(cs[i])
+        @test_throws TaskFailedException(task) wait(cs[i])
+        @test_throws TaskFailedException(task) take!(cs[i])
+        @test_throws TaskFailedException(task) put!(cs[i], 1)
+        N == 0 || @test_throws TaskFailedException(task) fetch(cs[i])
+        N == 0 && @test_throws ErrorException fetch(cs[i])
     end
 
     # Multiple tasks, first one to terminate closes the channel
@@ -245,10 +247,10 @@ using Distributed
         chnl = Channel{T}(tf6, N, taskref=taskref)
         put!(chnl, 2)
         yield()
-        @test_throws ErrorException wait(chnl)
+        @test_throws TaskFailedException(taskref[]) wait(chnl)
         @test istaskdone(taskref[])
         @test !isopen(chnl)
-        @test_throws ErrorException take!(chnl)
+        @test_throws TaskFailedException(taskref[]) take!(chnl)
     end
 end
 
diff --git a/test/file.jl b/test/file.jl
index 74a42cf7275a5..3a7b4710281b5 100644
--- a/test/file.jl
+++ b/test/file.jl
@@ -1298,7 +1298,7 @@ cd(dirwalk) do
     @test files == ["file1", "file2"]
 
     rm(joinpath("sub_dir1"), recursive=true)
-    @test_throws SystemError take!(chnl_error) # throws an error because sub_dir1 do not exist
+    @test_throws TaskFailedException take!(chnl_error) # throws an error because sub_dir1 do not exist
 
     root, dirs, files = take!(chnl_noerror)
     @test root == "."
diff --git a/test/worlds.jl b/test/worlds.jl
index 218d6d39d0783..2c3ed4bea7832 100644
--- a/test/worlds.jl
+++ b/test/worlds.jl
@@ -138,7 +138,7 @@ f265(::Int) = 1
 h265() = true
 loc_h265 = "$(@__FILE__):$(@__LINE__() - 1)"
 @test h265()
-@test_throws MethodError put_n_take!(h265, ())
+@test_throws TaskFailedException(t265) put_n_take!(h265, ())
 @test_throws TaskFailedException(t265) fetch(t265)
 @test istaskdone(t265)
 let ex = t265.exception

From d69e370d3f1295068ce54279a7d209751f28d435 Mon Sep 17 00:00:00 2001
From: Adam Beckmeyer <adam_gpg@thebeckmeyers.xyz>
Date: Thu, 19 Mar 2020 20:50:07 -0400
Subject: [PATCH 2/2] Fix broken bind doctest

---
 base/channels.jl | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/base/channels.jl b/base/channels.jl
index 8eabcc546edc3..db313776381f8 100644
--- a/base/channels.jl
+++ b/base/channels.jl
@@ -228,15 +228,16 @@ false
 ```jldoctest
 julia> c = Channel(0);
 
-julia> task = @async (put!(c,1);error("foo"));
+julia> task = @async (put!(c, 1); error("foo"));
 
-julia> bind(c,task);
+julia> bind(c, task);
 
 julia> take!(c)
 1
 
-julia> put!(c,1);
-ERROR: foo
+julia> put!(c, 1);
+ERROR: TaskFailedException:
+foo
 Stacktrace:
 [...]
 ```