See documentattion in header and comments in implementation for details.
This is actually done in preparation for floating ca derivations, not
multi-output fixed ca derivations, but the distinction doesn't yet
mattter.
Thanks @cole-h for finding and fixing a bunch of typos.
If you do a fetchTree on a Git repository, whether the result contains
a revCount attribute should not depend on whether that repository
happens to be a shallow clone or not. That would complicate caching a
lot and would be semantically messy. So applying fetchTree/fetchGit to
a shallow repository is now an error unless you pass the attribute
'shallow = true'. If 'shallow = true', we don't return revCount, even
if the repository is not actually shallow.
Note that Nix itself is not doing shallow clones at the moment. But it
could do so as an optimisation if the user specifies 'shallow = true'.
Issue #2988.
Today's fixed output derivations and regular derivations differ in a few
ways which are largely orthogonal. This replaces `isFixedOutput` with a
`type` that returns an enum of possible combinations.
In
nix-instantiate --dry-run '<nixpkgs/nixos/release-combined.nix>' -A nixos.tests.simple.x86_64-linux
this reduces time spent in unparse() from 9.15% to 4.31%. The main
culprit was appending characters one at a time to the destination
string. Even though the string has enough capacity, push_back() still
needs to check this on every call.
Note: like 'nix run', and unlike 'nix-shell', this takes an argv
vector rather than a shell command. So
nix dev-shell -c 'echo $PATH'
doesn't work. Instead you need to do
nix dev-shell -c bash -c 'echo $PATH'
The problem fixed: each nix-shell invocation creates a new temporary
directory (`/tmp/nix-shell-*`) and never cleans up.
And while I'm here, shellescape all variables inlined into the rcfile.
See what might happen without escaping:
$ export TZ="';echo pwned'"
$ nix-shell -p hello --run hello
pwned
Hello, world!
