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nix/doc/manual/rl-next/drv-string-parse-hang.md
pennae 79d3d412ca optimize derivation string parsing 
a bunch of derivation strings contain no escape sequences. we can
optimize for this fact by first scanning for the end of a derivation
string and simply returning the contents unmodified if no escape
sequences were found. to make this even more efficient we can also use
BackedStringViews to avoid copies, avoiding heap allocations for
transient data.

before:

Benchmark 1: nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
  Time (mean ± σ):      6.952 s ±  0.015 s    [User: 5.294 s, System: 1.452 s]
  Range (min … max):    6.926 s …  6.974 s    10 runs

after:

Benchmark 1: nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
  Time (mean ± σ):      6.907 s ±  0.012 s    [User: 5.272 s, System: 1.429 s]
  Range (min … max):    6.893 s …  6.926 s    10 runs
2023-12-30 18:44:10 +01:00

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synopsis prs
Fix handling of truncated `.drv` files. 9673

Previously a .drv that was truncated in the middle of a string would case nix to enter an infinite loop, eventually exhausting all memory and crashing.