build: remove expect as a dependency

I was packaging Lix 2.91 for nixpkgs and was annoyed at the expect
dependency. Turns out that you can replace unbuffer with a pretty-short
Python script.

It became less short after I found out that Linux was converting \n to
\r\n in the terminal subsystem, which was not very funny, but is at
least solved by twiddling termios bits.

Change-Id: I8a2700abcbbf6a9902e01b05b40fa9340c0ab90c

misc/meson.build

@@ -4,3 +4,9 @@ subdir('zsh')
 
 subdir('systemd')
 subdir('flake-registry')
+
+runinpty = configure_file(
+  copy : true,
+  input : meson.current_source_dir() / 'runinpty.py',
+  output : 'runinpty.py',
+)

misc/runinpty.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python3
+# SPDX-FileCopyrightText: 2001, 2002, 2003, 2004, 2005, 2006 Python Software Foundation; All Rights Reserved
+# SPDX-FileCopyrightText: 2024 Jade Lovelace
+# SPDX-License-Identifier: LGPL-2.1-or-later
+"""
+This script exists to lose Lix a dependency on expect(1) for the ability to run
+something in a pty.
+
+Yes, it could be replaced by script(1) but macOS and Linux script(1) have
+diverged sufficiently badly that even specifying a subcommand to run is not the
+same.
+"""
+import pty
+import sys
+import os
+from termios import ONLCR, ONLRET, ONOCR, OPOST, TCSAFLUSH, tcgetattr, tcsetattr
+from tty import setraw
+import termios
+
+def setup_terminal():
+    # does not matter which fd we use because we are in a fresh pty
+    modi = tcgetattr(pty.STDOUT_FILENO)
+    [iflag, oflag, cflag, lflag, ispeed, ospeed, cc] = modi
+
+    # Turning \n into \r\n is not cool, Linux!
+    oflag &= ~ONLCR
+    # I don't know what "implementation dependent postprocessing means" but it
+    # sounds bad
+    oflag &= ~OPOST
+    # Assume that NL performs the role of CR; do not insert CRs at column 0
+    oflag |= ONLRET | ONOCR
+
+    modi = [iflag, oflag, cflag, lflag, ispeed, ospeed, cc]
+
+    tcsetattr(pty.STDOUT_FILENO, TCSAFLUSH, modi)
+
+
+def spawn(argv: list[str]):
+    """
+    As opposed to pty.spawn, this one more seriously controls the pty settings.
+    Necessary to turn off such fun functionality as onlcr (LF to CRLF).
+
+    This is essentially copy pasted from pty.spawn, since there is no way to
+    hook the child pre-execve
+    """
+    pid, master_fd = pty.fork()
+    if pid == pty.CHILD:
+        setup_terminal()
+        os.execlp(argv[0], *argv)
+
+    try:
+        mode = tcgetattr(pty.STDIN_FILENO)
+        setraw(pty.STDIN_FILENO)
+        restore = True
+    except termios.error:
+        restore = False
+
+    try:
+        pty._copy(master_fd, pty._read, pty._read) # type: ignore
+    finally:
+        if restore:
+            tcsetattr(pty.STDIN_FILENO, TCSAFLUSH, mode) # type: ignore
+
+    os.close(master_fd)
+    return os.waitpid(pid, 0)[1]
+
+
+def main():
+    if len(sys.argv) == 1:
+        print(f'Usage: {sys.argv[0]} [command args]', file=sys.stderr)
+        sys.exit(1)
+
+    sys.exit(os.waitstatus_to_exitcode(spawn(sys.argv[1:])))
+
+
+if __name__ == '__main__':
+    main()

package.nix

@@ -20,7 +20,6 @@
   doxygen,
   editline-lix ? __forDefaults.editline-lix,
   editline,
-  expect,
   git,
   gtest,
   jq,
@@ -275,8 +274,6 @@ stdenv.mkDerivation (finalAttrs: {
     # configure, but we don't actually want to *run* the checks here.
     ++ lib.optionals lintInsteadOfBuild finalAttrs.checkInputs;
 
-  nativeCheckInputs = [ expect ];
-
   checkInputs = [
     gtest
     rapidcheck

tests/functional/common/vars-and-functions.sh.in

@@ -234,6 +234,10 @@ enableFeatures() {
     sed -i 's/experimental-features .*/& '"$features"'/' "$NIX_CONF_DIR"/nix.conf
 }
 
+runinpty() {
+    @python@ @runinpty@ "$@"
+}
+
 set -x
 
 onError() {

tests/functional/flakes/show.sh

@@ -104,7 +104,8 @@ cat >flake.nix<<EOF
   };
 }
 EOF
-unbuffer sh -c '
+
+runinpty sh -c '
   stty rows 20 cols 100
   nix flake show > show-output.txt
 '

tests/functional/meson.build

@@ -7,6 +7,8 @@ test_confdata = {
   'sandbox_shell': busybox.found() ? busybox.full_path() : '',
   'PACKAGE_VERSION': meson.project_version(),
   'system': host_system,
+  'python': python.full_path(),
+  'runinpty': runinpty.full_path(),
 }
 
 # Just configures `common/vars-and-functions.sh.in`.