[WIP] Port switch-to-configuration script to Python

nixos/modules/system/activation/top-level.nix

@@ -85,7 +85,7 @@ let
 
       mkdir $out/bin
       export localeArchive="${config.i18n.glibcLocales}/lib/locale/locale-archive"
-      substituteAll ${./switch-to-configuration.pl} $out/bin/switch-to-configuration
+      substituteAll ${./switch-to-configuration.py} $out/bin/switch-to-configuration
       chmod +x $out/bin/switch-to-configuration
 
       echo -n "${toString config.system.extraDependencies}" > $out/extra-dependencies
@@ -122,8 +122,9 @@ let
     configurationName = config.boot.loader.grub.configurationName;
 
     # Needed by switch-to-configuration.
-
-    perl = "${pkgs.perl}/bin/perl " + (concatMapStringsSep " " (lib: "-I${lib}/${pkgs.perl.libPrefix}") (with pkgs.perlPackages; [ FileSlurp NetDBus XMLParser XMLTwig ]));
+    python =
+      let env = pkgs.python3.withPackages (pypkgs: [ pypkgs.dbus-python ]);
+      in "${env}/bin/python3";
   };
 
   # Handle assertions and warnings

nixos/modules/system/etc/etc.nix

@@ -154,7 +154,7 @@ in
       ''
         # Set up the statically computed bits of /etc.
         echo "setting up /etc..."
-        ${pkgs.perl}/bin/perl -I${pkgs.perlPackages.FileSlurp}/lib/perl5/site_perl ${./setup-etc.pl} ${etc}/etc
+        ${pkgs.python3}/bin/python3 ${./setup-etc.py} ${etc}/etc
       '';
 
   };

nixos/modules/system/etc/setup-etc.py

@@ -0,0 +1,178 @@
+import argparse
+import os
+import os.path
+from pathlib import Path
+from pwd import getpwnam
+from grp import getgrnam
+import shutil
+import sys
+from typing import List, Tuple, Set
+
+STATIC = Path("/etc/static")
+CLEAN_FILE = Path("/etc/.clean")
+
+def warn(msg: str) -> None:
+    print('warning:', msg, file=sys.stderr)
+
+def atomic_symlink(source: Path, target: Path) -> None:
+    tmp = Path("{target}.tmp".format(target=target))
+    tmp.unlink()
+    tmp.symlink_to(source)
+    tmp.rename(target)
+
+def atomic_symlink_or_warn(source: Path, target: Path) -> None:
+    try:
+        atomic_symlink(source, target)
+    except IOError as exc:
+        warn("error creating link '{target}': {exc}". \
+             format(target=target, exc=exc))
+
+def is_static(path: Path) -> bool:
+    """
+    Returns True if the argument points to the files in /etc/static. That means
+    either argument is a symlink to a file in /etc/static or a directory with
+    all children being static.
+    """
+
+    if path.is_symlink():
+        target = path.resolve()
+        res = os.path.commonprefix([target, STATIC]) == STATIC  # type: bool
+        return res
+
+    if path.is_dir():
+        return all(is_static(ent) for ent in path.iterdir())
+
+    return False
+
+def cleanup() -> None:
+    """
+    Remove dangling symlinks that point to /etc/static.  These are
+    configuration files that existed in a previous configuration but not
+    in the current one.  For efficiency, don't look under /etc/nixos
+    (where all the NixOS sources live).
+    """
+    for root, dirs, files in os.walk('/etc'):
+        if root == '/etc':
+            dirs.remove('nixos')
+
+        for f in files:
+            path = Path(root) / Path(f)
+            if path.is_symlink():
+                target = path.resolve()
+                if os.path.commonprefix([target, STATIC]) == STATIC:
+                    x = STATIC / path.relative_to('/etc')
+                    if x.is_symlink():
+                        print("removing obsolete symlink '{path}'".format(path=path),
+                              file=sys.stderr)
+                        path.unlink()
+
+def link_statics(etc: Path) -> Tuple[Set[Path], Set[Path]]:
+    """
+    For every file in the etc tree, create a corresponding symlink in
+    /etc to /etc/static.  The indirection through /etc/static is to make
+    switching to a new configuration somewhat more atomic.
+    """
+
+    clean = open(CLEAN_FILE, 'a')
+    created = set()
+    copied = set()
+    for root, dirs, files in os.walk(etc):
+        for f in files:
+            path = Path(root) / Path(f)
+            if os.path.commonprefix([etc, path]) != etc:
+                continue
+            fn = path.relative_to(etc)
+            target = Path("/etc") / f
+            target.parent.mkdir(parents=True)
+            created.add(fn)
+
+            # Rename doesn't work if target is directory.
+            if Path(f).is_symlink() and target.is_dir():
+                if is_static(target):
+                    try:
+                        shutil.rmtree(target)
+                    except IOError as exc:
+                        warn("error trying to remove '{target}': {exc}". \
+                             format(target=target, exc=exc))
+                else:
+                    warn("$target directory contains user files. Symlinking may fail.")
+
+            meta_f = Path("{f}.mode".format(f=f))
+            if meta_f.exists():
+                mode = open(meta_f, 'r').read().strip()
+                if mode == 'direct-symlink':
+                    src = (STATIC / fn).resolve()
+                    atomic_symlink_or_warn(src, target)
+                else:
+                    user = open("{f}.uid".format(f=f)).read().strip()
+                    grp = open("{f}.gid".format(f=f)).read().strip()
+                    uid = getpwnam(user).pw_uid
+                    gid = getgrnam(grp).gr_gid
+
+                    src = STATIC / fn
+                    tmp = Path("{target}.tmp".format(target=target))
+                    try:
+                        shutil.copyfile(src, tmp)
+                    except IOError as exc:
+                        warn("error copying from '{src}' to '{tmp}': {exc}". \
+                             format(src=src, tmp=tmp, exc=exc))
+
+                    try:
+                        os.chown(tmp, uid, gid)
+                    except IOError as exc:
+                        warn("error setting owner of '{tmp}': {exc}". \
+                             format(tmp=tmp, exc=exc))
+
+                    try:
+                        os.chmod(tmp, int(mode, 8))
+                    except IOError as exc:
+                        warn("error setting mode of '{tmp}': {exc}". \
+                             format(tmp=tmp, exc=exc))
+
+                    try:
+                        tmp.rename(target)
+                    except IOError as exc:
+                        warn("error renaming '{tmp}' to '{target}': {exc}". \
+                             format(tmp=tmp, target=target, exc=exc))
+
+                copied.add(fn)
+                print(fn, file=clean)
+
+            elif Path(f).is_symlink():
+                atomic_symlink_or_warn(STATIC / fn, target)
+
+    return (created, copied)
+
+def main() -> None:
+    parser = argparse.ArgumentParser()
+    parser.add_argument('etc')
+    args = parser.parse_args()
+    etc = args.etc
+
+    # Atomically update /etc/static to point at the etc files of the
+    # current configuration.
+    atomic_symlink(etc, STATIC)
+
+    cleanup()
+
+    # Use /etc/.clean to keep track of copied files.
+    old_copied = []  # type: List[str]
+    if CLEAN_FILE.is_file():
+        old_copied += [ line.strip() for line in CLEAN_FILE.read_text().split('\n') ]
+
+    created, copied = link_statics(etc)
+
+    # Delete files that were copied in a previous version but not in the
+    # current.
+    for f in old_copied:
+        if f not in created:
+            fn = Path("/etc") / f
+            print("removing obsolete file '{f}'...".format(f=f),
+                  file=sys.stderr)
+            fn.unlink()
+
+    # Rewrite /etc/.clean
+    CLEAN_FILE.write_text('\n'.join(str(p) for p in copied))
+
+if __name__ == "__main__":
+    main()

pkgs/data/misc/shared-mime-info/default.nix

@@ -11,8 +11,9 @@ stdenv.mkDerivation rec {
   };
 
   nativeBuildInputs = [
-    pkgconfig gettext intltool perl perlXMLParser libxml2 glib
+    pkgconfig gettext intltool perl perlXMLParser
   ];
+  buildInputs = [ libxml2 glib ];
 
   meta = with stdenv.lib; {
     inherit version;

pkgs/development/libraries/dbus-glib/default.nix

@@ -11,7 +11,10 @@ stdenv.mkDerivation rec {
   outputs = [ "out" "dev" "devdoc" ];
   outputBin = "dev";
 
-  nativeBuildInputs = [ pkgconfig gettext ];
+  nativeBuildInputs = [
+    pkgconfig gettext
+    glib # for glib-marshal
+  ];
 
   buildInputs = [ expat libiconv ];
 

pkgs/development/tools/build-managers/meson/default.nix

@@ -47,10 +47,10 @@ python3Packages.buildPythonApplication rec {
 
   crossFile = writeTextDir "cross-file.conf" ''
     [binaries]
-    c = '${stdenv.cc.targetPrefix}cc'
-    cpp = '${stdenv.cc.targetPrefix}c++'
-    ar = '${stdenv.cc.bintools.targetPrefix}ar'
-    strip = '${stdenv.cc.bintools.targetPrefix}strip'
+    c = '${stdenv.targetPlatform.config}-cc'
+    cpp = '${stdenv.targetPlatform.config}-c++'
+    ar = '${stdenv.targetPlatform.config}-ar'
+    strip = '${stdenv.targetPlatform.config}-strip'
     pkgconfig = 'pkg-config'
 
     [properties]
@@ -70,7 +70,7 @@ python3Packages.buildPythonApplication rec {
 
   inherit (stdenv) cc;
 
-  isCross = stdenv.buildPlatform != stdenv.hostPlatform;
+  isCross = stdenv.targetPlatform != stdenv.hostPlatform;
 
   meta = with lib; {
     homepage = http://mesonbuild.com;