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1fe66852ff
since `up` and `values` are both pointer-aligned the type field will
also be pointer-aligned, wasting 48 bits of space on most machines. we
can get away with removing the type field altogether by encoding some
information into the `with` expr that created the env to begin with,
reducing the GC load for the absolutely massive amount of single-entry
envs we create for lambdas. this reduces memory usage of system eval by
quite a bit (reducing heap size of our system eval from 8.4GB to 8.23GB)
and gives similar savings in eval time.
running `nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'`
before:
Time (mean ± σ): 5.576 s ± 0.003 s [User: 5.197 s, System: 0.378 s]
Range (min … max): 5.572 s … 5.581 s 10 runs
after:
Time (mean ± σ): 5.408 s ± 0.002 s [User: 5.019 s, System: 0.388 s]
Range (min … max): 5.405 s … 5.411 s 10 runs
796 B
796 B
| synopsis | prs |
|---|---|
| Better error reporting for `with` expressions | 9658 |
with expressions using non-attrset values to resolve variables are now reported with proper positions.
Previously an incorrect with expression would report no position at all, making it hard to determine where the error originated:
nix-repl> with 1; a
error:
… <borked>
at «none»:0: (source not available)
error: value is an integer while a set was expected
Now position information is preserved and reported as with most other errors:
nix-repl> with 1; a
error:
… while evaluating the first subexpression of a with expression
at «string»:1:1:
1| with 1; a
| ^
error: value is an integer while a set was expected