cabal gen-bounds fails when using Nix integration

[mhwombat]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

$ cabal init --package-name=amy --exe

Guessing dependencies...

Generating LICENSE...
Warning: unknown license type, you must put a copy in LICENSE yourself.
Generating Setup.hs...
Generating CHANGELOG.md...
Generating Main.hs...
Generating amy.cabal...

Warning: no synopsis given. You should edit the .cabal file and add one.
You may want to edit the .cabal file and add a Description field.
$ cabal2nix --shell ./. >shell.nix
$ cabal --disable-nix gen-bounds
Congratulations, all your dependencies have upper bounds!
$ cabal --enable-nix gen-bounds
error: getting status of '/home/amy/temp/bug/dist/nix/shell.drv': No such file or directory

If you set nix: True in ~/.cabal/config you can get the same error.

$ cabal gen-bounds
error: getting status of '/home/amy/temp/bug/dist/nix/shell.drv': No such file or directory

Entering a nix shell first doesn't solve the problem.

$  nix-shell
(nix-shell) $ cabal gen-bounds
error: getting status of '/home/amy/temp/bug/dist/nix/shell.drv': No such file or directory

Here's a version with verbose output.

$ cabal gen-bounds --verbose=3
no user package environment file found at /home/amy/temp/bug
Searching for nix-shell in path.
Found nix-shell at /run/current-system/sw/bin/nix-shell
Environment: [("ASPELL_CONF","dict-dir /run/current-system/sw/lib/aspell"),("CABAL_IN_NIX_SHELL","1"),("COLORFGBG","15;0"),("CONDA_EXE","/home/amy/.conda/bin/conda"),("CONDA_PYTHON_EXE","/home/amy/.conda/bin/python"),("CONDA_SHLVL","0"),("CUPS_DATADIR","/nix/store/h0asy4z3wm6swx58w8rrizzi09lx0682-cups-progs/share/cups"),("DBUS_SESSION_BUS_ADDRESS","unix:abstract=/tmp/dbus-suCl44hswW,guid=92cdb6184e5434423b87a1a95ea1880c"),("DESKTOP_SESSION","/nix/store/drfh3rsvn5sxqkr488mxwgc6a96s8b8k-desktops/share/xsessions/none+xmonad"),("DISPLAY",":0"),("EDITOR","nano"),("GDK_PIXBUF_MODULE_FILE","/nix/store/kmhaf1l7r869z3mbf1ni1vys28qxv3bg-gdk-pixbuf-loaders.cache"),("GPG_TTY","/dev/pts/1"),("GTK_PATH","/home/amy/.nix-profile/lib/gtk-2.0:/home/amy/.nix-profile/lib/gtk-3.0:/etc/profiles/per-user/amy/lib/gtk-2.0:/etc/profiles/per-user/amy/lib/gtk-3.0:/nix/var/nix/profiles/default/lib/gtk-2.0:/nix/var/nix/profiles/default/lib/gtk-3.0:/run/current-system/sw/lib/gtk-2.0:/run/current-system/sw/lib/gtk-3.0"),("HOME","/home/amy"),("INFOPATH","/home/amy/.nix-profile/info:/home/amy/.nix-profile/share/info:/etc/profiles/per-user/amy/info:/etc/profiles/per-user/amy/share/info:/nix/var/nix/profiles/default/info:/nix/var/nix/profiles/default/share/info:/run/current-system/sw/info:/run/current-system/sw/share/info"),("JAVA_HOME","/nix/store/8zwjn10rg0pfkffp32y36i5hi5qv3rg9-openjdk-8u222-ga/lib/openjdk"),("KDEDIRS","/home/amy/.nix-profile:/etc/profiles/per-user/amy:/nix/var/nix/profiles/default:/run/current-system/sw"),("LANG","en_IE.UTF-8"),("LANGUAGE",""),("LD_LIBRARY_PATH","/run/opengl-driver/lib"),("LIBEXEC_PATH","/home/amy/.nix-profile/lib/libexec:/etc/profiles/per-user/amy/lib/libexec:/nix/var/nix/profiles/default/lib/libexec:/run/current-system/sw/lib/libexec"),("LOCALE_ARCHIVE","/run/current-system/sw/lib/locale/locale-archive"),("LOGNAME","amy"),("MOZ_PLUGIN_PATH","/home/amy/.nix-profile/lib/mozilla/plugins:/etc/profiles/per-user/amy/lib/mozilla/plugins:/nix/var/nix/profiles/default/lib/mozilla/plugins:/run/current-system/sw/lib/mozilla/plugins"),("NIXPKGS_CONFIG","/etc/nix/nixpkgs-config.nix"),("NIX_GHC","/nix/store/j3piwf6wmh8izrbw68j60jir7s89v4bi-ghc-8.6.5-with-packages/bin/ghc"),("NIX_PATH","/home/amy/.nix-defexpr/channels:nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos:nixos-config=/etc/nixos/configuration.nix:/nix/var/nix/profiles/per-user/root/channels"),("NIX_PROFILES","/run/current-system/sw /nix/var/nix/profiles/default /etc/profiles/per-user/amy /home/amy/.nix-profile"),("NIX_USER_PROFILE_DIR","/nix/var/nix/profiles/per-user/amy"),("NO_AT_BRIDGE","1"),("OLDPWD","/home/amy/temp"),("PAGER","less -R"),("PAM_KWALLET5_LOGIN","/run/user/1000/kwallet5.socket"),("PATH","/home/amy/.conda/condabin:/home/amy/wain-tools:/home/amy/bin:/home/amy/.local/bin:/home/amy/.cabal/bin:/home/amy/bin:/run/wrappers/bin:/home/amy/.nix-profile/bin:/etc/profiles/per-user/amy/bin:/nix/var/nix/profiles/default/bin:/run/current-system/sw/bin"),("PWD","/home/amy/temp/bug"),("QML2_IMPORT_PATH","/nix/store/m8k13rs90q9gjlww2gl4v0r635a6k6wh-qtwayland-5.12.3-bin/lib/qt-5.12.3/qml:/nix/store/bsvszl5vrbddniywfmwiac4xc4wzk9dy-qtquickcontrols-5.12.3/lib/qt-5.12.3/qml:/nix/store/20xwh0i8q1drhwwa57sqnz96bgy49rq7-qtdeclarative-5.12.3-bin/lib/qt-5.12.3/qml"),("QTWEBKIT_PLUGIN_PATH","/home/amy/.nix-profile/lib/mozilla/plugins/:/etc/profiles/per-user/amy/lib/mozilla/plugins/:/nix/var/nix/profiles/default/lib/mozilla/plugins/:/run/current-system/sw/lib/mozilla/plugins/"),("QT_PLUGIN_PATH","/nix/store/m8k13rs90q9gjlww2gl4v0r635a6k6wh-qtwayland-5.12.3-bin/lib/qt-5.12.3/plugins:/nix/store/20xwh0i8q1drhwwa57sqnz96bgy49rq7-qtdeclarative-5.12.3-bin/lib/qt-5.12.3/plugins:/nix/store/rk4z6ciz36v323lgp19rxb50kjl95knd-qtsvg-5.12.3-bin/lib/qt-5.12.3/plugins:/nix/store/phh1320xs4zwgkb7adnbrwyhxqcw3yh6-qtbase-5.12.3-bin/lib/qt-5.12.3/plugins:/home/amy/.nix-profile/lib/qt4/plugins:/home/amy/.nix-profile/lib/kde4/plugins:/etc/profiles/per-user/amy/lib/qt4/plugins:/etc/profiles/per-user/amy/lib/kde4/plugins:/nix/var/nix/profiles/default/lib/qt4/plugins:/nix/var/nix/profiles/default/lib/kde4/plugins:/run/current-system/sw/lib/qt4/plugins:/run/current-system/sw/lib/kde4/plugins"),("SHELL","/run/current-system/sw/bin/bash"),("SHLVL","5"),("SSH_ASKPASS","/nix/store/mkszwkdz3lb51xbq4s0wal1762xv5azy-ksshaskpass-5.16.5/bin/ksshaskpass"),("STRIGI_PLUGIN_PATH","/home/amy/.nix-profile/lib/strigi/:/etc/profiles/per-user/amy/lib/strigi/:/nix/var/nix/profiles/default/lib/strigi/:/run/current-system/sw/lib/strigi/"),("TERM","xterm-256color"),("TERMINFO_DIRS","/home/amy/.nix-profile/share/terminfo:/etc/profiles/per-user/amy/share/terminfo:/nix/var/nix/profiles/default/share/terminfo:/run/current-system/sw/share/terminfo"),("TZDIR","/etc/zoneinfo"),("USER","amy"),("WINDOWID","0"),("XAUTHORITY","/home/amy/.Xauthority"),("XCURSOR_PATH","/home/amy/.icons:/home/amy/.nix-profile/share/icons:/etc/profiles/per-user/amy/share/icons:/nix/var/nix/profiles/default/share/icons:/run/current-system/sw/share/icons"),("XDG_CONFIG_DIRS","/etc/xdg:/home/amy/.nix-profile/etc/xdg:/etc/profiles/per-user/amy/etc/xdg:/nix/var/nix/profiles/default/etc/xdg:/run/current-system/sw/etc/xdg"),("XDG_CURRENT_DESKTOP",""),("XDG_DATA_DIRS","/nix/store/y8zw0g688v7js1sni9gndhib1nfgr3xm-qterminal-0.14.1/share:/home/amy/.nix-profile/share:/etc/profiles/per-user/amy/share:/nix/var/nix/profiles/default/share:/run/current-system/sw/share"),("XDG_DESKTOP_PORTAL_PATH","/nix/store/x13ld6p8kkahngi8ak5w4vr7l6y8pll7-xdg-desktop-portal-kde-5.16.5/share/xdg-desktop-portal/portals"),("XDG_RUNTIME_DIR","/run/user/1000"),("XDG_SEAT","seat0"),("XDG_SEAT_PATH","/org/freedesktop/DisplayManager/Seat0"),("XDG_SESSION_CLASS","user"),("XDG_SESSION_DESKTOP",""),("XDG_SESSION_ID","2"),("XDG_SESSION_PATH","/org/freedesktop/DisplayManager/Session1"),("XDG_SESSION_TYPE","x11"),("XDG_VTNR","7"),("XMONAD_XMESSAGE","/nix/store/zzi56zjrpcdk63xxikvy31v9yn67ky0l-xmessage-1.0.5/bin/xmessage"),("_","/run/current-system/sw/bin/cabal"),("_CE_CONDA",""),("_CE_M",""),("__ETC_PROFILE_DONE","1"),("__NIXOS_SET_ENVIRONMENT_DONE","1")]
/run/current-system/sw/bin/nix-shell --add-root dist/nix/gcroots/result --indirect /home/amy/temp/bug/dist/nix/shell.drv --run '/nix/store/yslccq49f6dv12ay6h5f1nidgnnf1dl4-cabal-install-3.0.0.0/bin/cabal gen-bounds '\''--verbose=3'\'''
error: getting status of '/home/amy/temp/bug/dist/nix/shell.drv': No such file or directory
/run/current-system/sw/bin/nix-shell returned ExitFailure 1

Expected behavior
I expect cabal --enable-nix gen-bounds to produce the same output as cabal --disable-nix gen-bounds. I don't understand why this this particular command would be looking for a .drv file. I would have thought that it only needs to examine the .cabal file.

System information

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 8.6.5
$ cabal --version
cabal-install version 3.0.0.0
compiled using version 3.0.0.0 of the Cabal library
$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 4.19.116, NixOS, 19.09.2426.9237a09d8ed (Loris)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.3`
 - channels(amy): `"nixpkgs-18.09.1676.7e88992a8c7"`
 - channels(root): `"nixos-19.09.2426.9237a09d8ed"`
 - nixpkgs: `/home/amy/.nix-defexpr/channels/nixpkgs`

Additional context
Add any other context about the problem here.

[23Skidoo]

/cc @mightybyte

[mhwombat]

I'm still experiencing this issue. In the meantime, I'm using the cabal --disable-nix gen-bounds workaround.

[Kleidukos]

This bug is still around

[Mikolaj]

Does anybody have an idea if this is blocked on something? Did someone mention exact-print as the blocker?

[gbaz]

I don't think it is blocked on anything. That said, I'm not sure it is a bug. When --enable-nix is set, all commands are run in a subprocess, after nix-shell has been entered, using shell.drv.

So any cabal command enters the nix-shell this way when --enable-nix is set. Correspondingly any cabal command would fail this way if the drv were missing.

In which case this bug report is just that this particular command fails that way?

[Mikolaj]

Is gen-bounds a v2- command? Because --enable-nix is supposed to be ignored by v2- commands (or is supposed to be broken with v2- commands?). See, e.g., #6444 and #4646.

[fgaz]

It doesn't have a v1-/v2- distinction. It's a very simple command that reads a single cabal file and doesn't accept any flag except global ones
edit: i guess you could call it v1- since it doesn't work in projects

[Mikolaj]

@mhwombat: I'm trying to understand what severity this issue has and so if the workaround is sufficient. Is the main problem for you that you want to keep nix: True in ~/.cabal/config permanently, but run some commands (e.g., gen-bounds) as if you had nix: False, because nix: True requires some setup per package checkout that you may not need to perform otherwise? Or is the burden more general or heavier?

[Mikolaj]

BTW, people report in #4646 and other tickets with the nix label that nix: True is useless for them. Are you sure it still has any value for you with newer cabal versions?

[mhwombat]

@Mikolaj Thank you for following up on this. For me, it's just a minor annoyance to have to specify --disable-nix for this command. I didn't expect this particular command to need the .drv file, so the error message didn't help me, and the only way I found the solution was by searching the web.

My suggestions for resolving this are, in decreasing order of preference:

1. Don't go looking for a .drv file (so don't enter a shell?) unless you need to.
2. Have the error message suggest the --disable-nix workaround.
3. Document the workaround in, say, https://cabal.readthedocs.io/en/3.6/cabal-package.html?highlight=gen-bounds#generating-dependency-version-bounds.
4. Close the issue as "won't fix". Once you know the workaround, it's only an annoyance.

I don't bother with the nix: True flag these days.

[Mikolaj]

I'm asking, in particular, because we recently debated whether to remove --enable-nix (will probably happen in the long run) or to improve the docs and we ended up with #8333, which is probably incorrect in light of your experience. Or at least could be improved, which would also be a way to put this ticket to rest and make it easier for people to find an answer in a similar situation.