Merge pull request #85 from DrChainsaw/exceptionunwrap

fix exception unwrapping

Author: DrChainsaw

src/parallelism.jl

@@ -38,12 +38,31 @@ exec(e, x, args...) = x
 exec(e, d::FileTree, args...) = mapvalues(v -> exec(e, v, fetch), d; lazy=false)
 exec(e, f::File, collect_results=fetch) = setvalue(f, exec(e, f[], collect_results))
 
+struct UnwrappedTaskException{E} <: Exception
+    cnt::Int
+    msg::String
+    stack::E
+end
+
+function Base.showerror(io::IO, e::UnwrappedTaskException)
+    println(io, e.cnt, " nested TaskFailedExceptions have been unwrapped by FileTrees to reduce clutter!\n",  e.msg)
+    for (wrapped, bt) in Iterators.reverse(e.stack)
+        showerror(io, wrapped, bt; backtrace=bt !== nothing)
+    end
+end
+
 fetch_unwrap_exception(t) = try
     fetch(t)
 catch e
-    if istaskfailed(t)
-        rethrow(t.result)
+    if e isa TaskFailedException
+        lastthrown = first(current_exceptions(t)).exception
+        if lastthrown isa UnwrappedTaskException
+            rethrow(UnwrappedTaskException(lastthrown.cnt + 1, lastthrown.msg, lastthrown.stack))
+        end
+        # kept msg in case other executors also want to unwrap
+        rethrow(UnwrappedTaskException(1, "See Executor.Threads documentation for how to disable unwrapping case anything appears to be missing.", current_exceptions(t)))
     end
+    rethrow(e)
 end
 
 """

test/basics.jl

@@ -257,6 +257,24 @@ import Dagger
     end
 end
 
+@testset "Unwrap TaskFailedExceptions" begin
+        innerfun(x) = x + 2  # Error, we will pass a string as x
+        outerfun(x) = string("Result ", innerfun(x))
+        # Only Executors.Threads messes with exceptions, so we don't test this above
+        callsitefun(ft) = exec(Executor.Threads(unwrap_exceptions=true), mapvalues(identity, mapvalues(identity, mapvalues(identity, mapvalues(outerfun, ft)))))
+        t1 = FileTrees.load(uppercase∘path, t, lazy=true)
+    try
+        callsitefun(t1)
+    catch ex
+        # Bleh! Is there no better way to test that functions show up in the backtrace?
+        currbt = stacktrace(catch_backtrace())
+        @test any(s -> s.func == Symbol(callsitefun), currbt)
+        exstr = sprint(showerror, ex)
+        @test occursin(string(outerfun), exstr)
+        @test occursin(string(innerfun), exstr)
+    end
+end
+
 
 @testset "iterators" begin
     @test values(t1) == map(get, filter(hasvalue, nodes(t1)))