Add throw option in wait(::Task) (JuliaLang#53685)

As we discussed with @vtjnash in PR JuliaLang#53341, it might be useful to
introduce the `throw` option in the `wait` function for `Task`. If
`throw=false` is specified, `wait` behaves like `_wait`; it prevents
throwing a `TaskFailedException`.

Author: mrkn

base/condition.jl

@@ -113,7 +113,9 @@ Block the current task until some event occurs, depending on the type of the arg
 * `Process`: Wait for a process or process chain to exit. The `exitcode` field of a process
   can be used to determine success or failure.
 * [`Task`](@ref): Wait for a `Task` to finish. If the task fails with an exception, a
-  `TaskFailedException` (which wraps the failed task) is thrown.
+  `TaskFailedException` (which wraps the failed task) is thrown.  Waiting on a task
+  additionally allows passing `throw=false` which prevents throwing a `TaskFailedException`
+  when the task fails.
 * [`RawFD`](@ref): Wait for changes on a file descriptor (see the `FileWatching` package).
 
 If no argument is passed, the task blocks for an undefined period. A task can only be

base/task.jl

@@ -356,11 +356,11 @@ function _wait2(t::Task, waiter::Task)
     nothing
 end
 
-function wait(t::Task)
+function wait(t::Task; throw=true)
     t === current_task() && error("deadlock detected: cannot wait on current task")
     _wait(t)
-    if istaskfailed(t)
-        throw(TaskFailedException(t))
+    if throw && istaskfailed(t)
+        Core.throw(TaskFailedException(t))
     end
     nothing
 end

test/threads.jl

@@ -341,3 +341,16 @@ end
 @testset "Base.Threads docstrings" begin
     @test isempty(Docs.undocumented_names(Threads))
 end
+
+@testset "wait failed task" begin
+    @testset "wait without throw keyword" begin
+        t = Threads.@spawn error("Error")
+        @test_throws TaskFailedException wait(t)
+    end
+
+    @testset "wait with throw=false" begin
+        t = Threads.@spawn error("Error")
+        wait(t; throw=false)
+        @test istaskfailed(t)
+    end
+end