Previously an expression like 'x: y: ...' would create two
environments with one value. Now it creates one environment with two
values. This reduces the number of allocations and the distance in the
environment chain that variable lookups need to traverse.
On
$ nix-instantiate --dry-run '<nixpkgs/nixos/release-combined.nix>' -A nixos.tests.simple.x86_64-linux
this gives a ~30% reduction in the number of Env allocations.
We now parse function applications as a vector of arguments rather
than as a chain of binary applications, e.g. 'substring 1 2 "foo"' is
parsed as
ExprCall { .fun = <substring>, .args = [ <1>, <2>, <"foo"> ] }
rather than
ExprApp (ExprApp (ExprApp <substring> <1>) <2>) <"foo">
This allows primops to be called immediately (if enough arguments are
supplied) without having to allocate intermediate tPrimOpApp values.
On
$ nix-instantiate --dry-run '<nixpkgs/nixos/release-combined.nix>' -A nixos.tests.simple.x86_64-linux
this gives a substantial performance improvement:
user CPU time: median = 0.9209 mean = 0.9218 stddev = 0.0073 min = 0.9086 max = 0.9340 [rejected, p=0.00000, Δ=-0.21433±0.00677]
elapsed time: median = 1.0585 mean = 1.0584 stddev = 0.0024 min = 1.0523 max = 1.0623 [rejected, p=0.00000, Δ=-0.20594±0.00236]
because it reduces the number of tPrimOpApp allocations from 551990 to
42534 (i.e. only small minority of primop calls are partially
applied) which in turn reduces time spent in the garbage collector.
This is in line with XDG Base Directory Specification, where ~/.config is supposed to be used when XDG_CONFIG_HOME is unset.
It also better matches the reality, where ~/.config/nix.conf does not seem to be used.
ShellCheck correctly warns:
In scripts/install-nix-from-closure.sh line 218:
echo -e "\nif [ -e $p ]; then . $p; fi # added by Nix installer" >> "$fn"
^-- SC3037: In POSIX sh, echo flags are undefined.
In scripts/install-nix-from-closure.sh line 229:
echo -e "\nif [ -e $p ]; then . $p; fi # added by Nix installer" >> "$fn"
^-- SC3037: In POSIX sh, echo flags are undefined.
Indeed, this actually breaks on Ubuntu where /bin/sh is dash.
Fixes#5458.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
