allow redirect_std* to devnull (#36136) (#36146)

Author: KlausC

base/stream.jl

@@ -1098,6 +1098,15 @@ for (x, writable, unix_fd, c_symbol) in
             ($f)($(writable ? :write : :read))
             return (read, write)
         end
+        function ($f)(::DevNull)
+            global $x
+            nulldev = @static Sys.iswindows() ? "NUL" : "/dev/null"
+            handle = open(nulldev, write=$writable)
+            $(_f)(handle)
+            close(handle) # handle has been dup'ed in $(_f)
+            $x = devnull
+            return devnull
+        end
     end
 end
 
@@ -1115,7 +1124,7 @@ elsewhere.
 If called with the optional `stream` argument, then returns `stream` itself.
 
 !!! note
-    `stream` must be a `TTY`, a `Pipe`, or a socket.
+    `stream` must be an `IOStream`, a `TTY`, a `Pipe`, a socket, or `devnull`.
 """
 redirect_stdout
 
@@ -1125,7 +1134,7 @@ redirect_stdout
 Like [`redirect_stdout`](@ref), but for [`stderr`](@ref).
 
 !!! note
-    `stream` must be a `TTY`, a `Pipe`, or a socket.
+    `stream` must be an `IOStream`, a `TTY`, a `Pipe`, a socket, or `devnull`.
 """
 redirect_stderr
 
@@ -1137,7 +1146,7 @@ Note that the order of the return tuple is still `(rd, wr)`,
 i.e. data to be read from [`stdin`](@ref) may be written to `wr`.
 
 !!! note
-    `stream` must be a `TTY`, a `Pipe`, or a socket.
+    `stream` must be an `IOStream`, a `TTY`, a `Pipe`, a socket, or `devnull`.
 """
 redirect_stdin
 

test/spawn.jl

@@ -255,6 +255,19 @@ end
     end
 end
 
+# issue #36136
+@testset "redirect to devnull" begin
+    @test redirect_stdout(devnull) do; println("Hello") end === nothing
+    @test redirect_stderr(devnull) do; println(stderr, "Hello") end === nothing
+    # stdin is unavailable on the workers. Run test on master.
+    ret = Core.eval(Main, quote
+                remotecall_fetch(1) do
+                    redirect_stdin(devnull) do; read(stdin, String) end
+                end
+            end)
+    @test ret == ""
+end
+
 # Test that redirecting an IOStream does not crash the process
 let fname = tempname(), p
     cmd = """