https://hydra.nixos.org/build/59649086

https://hydra.nixos.org/build/59649086

This is useful for testing commands in isolation.

For example,

  $ nix run nixpkgs.geeqie -i -k DISPLAY -k XAUTHORITY -c geeqie

runs geeqie in an empty environment, except for $DISPLAY and
$XAUTHORITY.

E.g.

  nix run nixpkgs.hello -c hello --greeting Hallo

Note that unlike "nix-shell --command", no quoting of arguments is
necessary.

"-c" (short for "--command") cannot be combined with "--" because they
both consume all remaining arguments. But since installables shouldn't
start with a dash, this is unlikely to cause problems.

Running "nix run" with a diverted store, e.g.

  $ nix run --store local?root=/tmp/nix nixpkgs.hello

stopped working when Nix became multithreaded, because
unshare(CLONE_NEWUSER) doesn't work in multithreaded processes. The
obvious solution is to terminate all other threads first, but 1) there
is no way to terminate Boehm GC marker threads; and 2) it appears that
the kernel has a race where unshare(CLONE_NEWUSER) will still fail for
some indeterminate amount of time after joining other threads.

So instead, "nix run" will now exec() a single-threaded helper ("nix
__run_in_chroot") that performs the actual unshare()/chroot()/exec().

These are assumed to be internal.

Symlinks like /proc/self/exe report a stat() size of 0, so use a
buffer of at least PATH_MAX instead.

And print them (separately from the progress bar) given sufficient -v
flags.

This makes the progress bar work for non-root users.

Now that we use threads in lots of places, it's possible for
TunnelLogger::log() to be called asynchronously from other threads
than the main loop. So we need to ensure that STDERR_NEXT messages
don't clobber other messages.

So the progress bar can show

  [1/0/1 built, 0.0 MiB DL] building hello-2.10 (configuring): checking whether pread is declared without a macro... yes

In particular, this allows more relevant activities ("substituting X")
to supersede inferior ones ("downloading X").

https://hydra.nixos.org/build/59390148

This allows the progress bar to display "building perl-5.22.3" instead
of "building /nix/store/<hash>-perl-5.22.3.drv".

Actually, currently they can only create download activities. Thus,
downloads by builtins.fetchurl show up in the progress bar.

Remove nix-mode.el from Nix.

This removes the file nix-mode.el from Nix. The file is now available within the
repository https://github.com/NixOS/nix-mode.

Fixes #662
Fixes #1040
Fixes #1054
Fixes #1055
Closes #1119
Fixes #1419

NOTE: all of the above should be fixed within NixOS/nix-mode. If one of those
hasn’t please reopen within NixOS/nix-mode and not within NixOS/nix.

update MD5 to SHA-256 in expression-syntax

Remove unused decodeOctalEscaped

Besides being unused, this function has a bug that it will incorrectly
decode the path component Ubuntu\04016.04.2\040LTS\040amd64 as
"Ubuntu.04.2 LTS amd64" instead of "Ubuntu 16.04.2 LTS amd64".

This replaces "nix-store --optimise". Main difference is that it has a
progress indicator.