lib: improve filterAttrs

[h7x4]

Description of changes

Small optimization. Instead of having filterAttrs collect values and merge them, it only collects the names of the unwanted attributes and passes them to removeAttrs. This leads to slightly less memory copied around. Also added a test

NIX_SHOW_STATS=1 nix flake check before

{
  "cpuTime": 10.154743194580078,
  "envs": {
    "bytes": 693836664,
    "elements": 35023599,
    "number": 25852992
  },
  "gc": {
    "heapSize": 789245952,
    "totalBytes": 3407736128
  },
  "list": {
    "bytes": 60538296,
    "concats": 866078,
    "elements": 7567287
  },
  "nrAvoided": 28680092,
  "nrFunctionCalls": 23458684,
  "nrLookups": 11705269,
  "nrOpUpdateValuesCopied": 32773039,
  "nrOpUpdates": 1231329,
  "nrPrimOpCalls": 11339176,
  "nrThunks": 27686197,
  "sets": {
    "bytes": 913395872,
    "elements": 51894915,
    "number": 5192327
  },
  "sizes": {
    "Attr": 16,
    "Bindings": 16,
    "Env": 16,
    "Value": 24
  },
  "symbols": {
    "bytes": 1220932,
    "number": 99185
  },
  "values": {
    "bytes": 1055012784,
    "number": 43958866
  }
}

NIX_SHOW_STATS=1 nix flake check after

{
  "cpuTime": 10.344867706298828,
  "envs": {
    "bytes": 691711896,
    "elements": 34935067,
    "number": 25764460
  },
  "gc": {
    "heapSize": 738914304,
    "totalBytes": 3402504560
  },
  "list": {
    "bytes": 60176696,
    "concats": 866078,
    "elements": 7522087
  },
  "nrAvoided": 28543943,
  "nrFunctionCalls": 23401274,
  "nrLookups": 11712564,
  "nrOpUpdateValuesCopied": 32773039,
  "nrOpUpdates": 1231329,
  "nrPrimOpCalls": 11339176,
  "nrThunks": 27657492,
  "sets": {
    "bytes": 912128368,
    "elements": 51843610,
    "number": 5164413
  },
  "sizes": {
    "Attr": 16,
    "Bindings": 16,
    "Env": 16,
    "Value": 24
  },
  "symbols": {
    "bytes": 1220945,
    "number": 99186
  },
  "values": {
    "bytes": 1054323864,
    "number": 43930161
  }
}

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[infinisil]

Neat!