From 80062128fea1c576dd465f8278445a3cccd04161 Mon Sep 17 00:00:00 2001
From: Pat Maddox <pat@patmaddox.com>
Date: Fri, 30 Jan 2026 03:33:23 -0800
Subject: [PATCH] jobserver: Support GNU Make 4.3+ fifo jobserver format

GNU Make 4.3+ uses named pipes for the jobserver, with the format
--jobserver-auth=fifo:/path/to/pipe instead of the traditional
--jobserver-auth=R,W format using inherited file descriptors.

Prior to this, the test suite failed with:

gmake: warning: -j10 forced in submake: resetting jobserver mode.
redo x
Traceback (most recent call last):
  File "apenwarr-redo/default.jj/bin/redo", line 10, in <module>
    redo.cmd_redo.main()
  File "apenwarr-redo/default.jj/bin/../redo/cmd_redo.py", line
107, in main
    jobserver.setup(j)
  File "apenwarr-redo/default.jj/bin/../redo/jobserver.py", line
 230, in setup
    (a, b) = arg.split(',', 1)
    ^^^^^^
ValueError: not enough values to unpack (expected 2, got 1)
gmake: *** [Makefile:7: y] Error 1
---
 redo/jobserver.py | 40 +++++++++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 13 deletions(-)

diff --git a/redo/jobserver.py b/redo/jobserver.py
index 6dc30b6..874859f 100644
--- a/redo/jobserver.py
+++ b/redo/jobserver.py
@@ -227,19 +227,33 @@ def setup(maxjobs):
     if ofs >= 0:
         s = flags[ofs+len(FIND):]
         (arg, junk) = s.split(' ', 1)
-        (a, b) = arg.split(',', 1)
-        a = atoi(a)
-        b = atoi(b)
-        if a <= 0 or b <= 0:
-            logs.err('invalid --jobserver-auth: %r\n' % arg)
-            raise helpers.ImmediateReturn(200)
-        if not helpers.fd_exists(a) or not helpers.fd_exists(b):
-            logs.err('broken --jobserver-auth from parent process:\n')
-            logs.err('  using GNU make? prefix your Makefile rule with "+"\n')
-            logs.err(
-                '  otherwise, see ' +
-                'https://redo.rtfd.io/en/latest/FAQParallel/#MAKEFLAGS\n')
-            raise helpers.ImmediateReturn(200)
+        if arg.startswith('fifo:'):
+            # GNU Make 4.3+ named pipe jobserver format: fifo:/path/to/pipe
+            fifo_path = arg[5:]
+            try:
+                # Open the named pipe for both reading and writing.
+                # O_RDWR avoids blocking that would occur with O_RDONLY.
+                fd = os.open(fifo_path, os.O_RDWR)
+                a = fd
+                b = fd
+            except OSError as e:
+                logs.err('cannot open jobserver fifo %r: %s\n' % (fifo_path, e))
+                raise helpers.ImmediateReturn(200)
+        else:
+            # Traditional pipe jobserver format: R,W (two file descriptors)
+            (a, b) = arg.split(',', 1)
+            a = atoi(a)
+            b = atoi(b)
+            if a <= 0 or b <= 0:
+                logs.err('invalid --jobserver-auth: %r\n' % arg)
+                raise helpers.ImmediateReturn(200)
+            if not helpers.fd_exists(a) or not helpers.fd_exists(b):
+                logs.err('broken --jobserver-auth from parent process:\n')
+                logs.err('  using GNU make? prefix your Makefile rule with "+"\n')
+                logs.err(
+                    '  otherwise, see ' +
+                    'https://redo.rtfd.io/en/latest/FAQParallel/#MAKEFLAGS\n')
+                raise helpers.ImmediateReturn(200)
         if maxjobs == 1:
             # user requested exactly one token, which means they want to
             # serialize us, even if the parent redo is running in parallel.