nix-shell -p: unsafeDiscardStringContext missing error

[fkarg]

Describe the bug
Whatever I'm trying to do right now (with nix-shell -p or nix-env -iA), I encounter the following error:

error: attribute 'unsafeDiscardStringContext' missing, at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/strings.nix:429:13
(use '--show-trace' to show detailed location information)

To Reproduce
Honestly, no idea. But I now have it when using nix on my laptop (NixOS) as well as on my other laptop (Ubuntu with nix). So ... I don't think this is isolated.

I was experimenting with a number of things on my NixOS at first, so I thought it was because I was doing something wrong - but the same error without experimenting with only nix installed? Something weird is going on.

Expected behavior
No Error Message when using nix-shell -p or other stuff.

Additional Context

I tried nix-channel --update to no avail.
nix-env -iA nixpkgs.XXX throws the same error.

Installing packages with the path provided from NixDB works (?), if I wouldn't interrupt it after downloading dozens of GB in two hours (and no, it should not have done this for that package).

Metadata

$ nix-shell -p nix-info --run "nix-info -m" --show-trace
error: while evaluating anonymous function at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/top-level/impure.nix:15:1, called from (string):1:6:
while evaluating anonymous function at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/top-level/default.nix:19:1, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/top-level/impure.nix:83:1:
while evaluating anonymous function at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/stdenv/booter.nix:42:1, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/top-level/default.nix:122:10:
while evaluating 'dfold' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/stdenv/booter.nix:60:27, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/stdenv/booter.nix:136:4:
while evaluating 'go' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/stdenv/booter.nix:63:18, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/stdenv/booter.nix:72:13:
while evaluating 'imap1' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/lists.nix:116:14, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/stdenv/booter.nix:78:30:
while evaluating 'reverseList' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/lists.nix:393:17, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/stdenv/booter.nix:85:6:
while evaluating anonymous function at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/stdenv/default.nix:7:1, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/top-level/default.nix:118:12:
while evaluating 'elaborate' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/systems/default.nix:18:15, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/pkgs/top-level/default.nix:52:17:
while evaluating 'foldl' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/lists.nix:80:20, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/systems/default.nix:149:13:
while evaluating 'foldl'' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/lists.nix:82:16, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/lists.nix:86:8:
while evaluating the attribute 'parsed.abi.assertions' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/systems/default.nix:23:7:
while evaluating 'mkSystemFromString' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/systems/parse.nix:453:24, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/systems/default.nix:23:16:
while evaluating 'mkSkeletonFromList' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/systems/parse.nix:374:24, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/systems/parse.nix:453:49:
while evaluating 'splitString' at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/strings.nix:427:23, called from /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/systems/parse.nix:453:69:
attribute 'unsafeDiscardStringContext' missing, at /nix/store/ncj4504zgiabs2dm7ya60k83cpc59vlz-nixpkgs-21.05pre282987.294d1925af6/nixpkgs/lib/strings.nix:429:13

Well. I'll happily provide any other information.

[SFrijters]

This looks like it might be (related to) #118481 ?

[sternenseemann]

Usually this happens when the running nix-daemon and the nix-shell you are running go out of sync in a significant way. This is often triggered by a nix-env -u which hits the mentioned issue. A rollback of your environment should resolve this issue.

What does readlink $(type -p nix-shell) print? Have you tried restarting your nix-daemon?

[fkarg]

Thanks for the help! The in #118481 mentioned nix-env --rollback and restarting nix-daemon somehow did the trick, and everything is working properly now.