Performance: Replace `./` with `self` flake input to improve evaluation speed

[anntnzrb]

Summary

When using snowfall-lib with mkFlake, Nix shows performance warnings suggesting faster evaluation could be achieved by replacing ./ path references with the self flake input or builtins.path.

Warning Details

warning: Copying '«github:snowfallorg/lib/02d941739f98a09e81f3d2d9b3ab08918958beac?narHash=sha256-4i9nAJEZFv7vZMmrE0YG55I3Ggrtfo5/T07JEpEZ/RM%3D»/nix/store/dmwivyifr88a7mr2f851gcm6q2ig9hbc-source' to the store again
You can make Nix evaluate faster and copy fewer files by replacing \`./.\` with the \`self\` flake input, or \`builtins.path { path = ./.; name = \"source\"; }\`

Location: «github:snowfallorg/lib/02d941739f98a09e81f3d2d9b3ab08918958beac?narHash=sha256-4i9nAJEZFv7vZMmrE0YG55I3Ggrtfo5/T07JEpEZ/RM%3D»/nix/store/dmwivyifr88a7mr2f851gcm6q2ig9hbc-source/flake.nix:21:15

Root Cause

In flake.nix line 17, snowfall-lib uses:

core-inputs =
  inputs
  // {
    src = ./.;  # <-- This causes the warning
  };

The warning originates from this usage of ./ which causes Nix to copy the entire directory tree to the store on each evaluation.

Proposed Solution

Replace the src = ./.; with one of the recommended optimizations:

Option 1: Use builtins.path (immediate fix)

core-inputs =
  inputs
  // {
    src = builtins.path { path = ./.; name = "source"; };
  };

Option 2: Use self flake input (requires architecture changes)

# Would need to investigate how to properly pass self to mkLib
# This might require changes to the mkFlake interface

Impact

• Performance: Faster Nix evaluation times
• Storage: Reduced unnecessary copying to Nix store
• User Experience: Eliminates warning messages for all users
• Frequency: Appears on every nix build, home-manager switch, etc.

Environment

• snowfall-lib version: Latest main (commit 02d9417)
• Nix version: 2.18+ (warnings appear in modern Nix versions)
• Reproducible: Yes, affects all users of snowfall-lib

Additional Context

This warning appears to be related to Nix's evaluation cache improvements and affects any flake using snowfall-lib. The functionality works correctly, but the optimization would improve performance for all users.

There may be similar issues in other parts of the codebase where ./ is used instead of more optimized alternatives.

References

• Related to Nix evaluation cache: https://www.tweag.io/blog/2020-06-25-eval-cache/
• Nix manual on flake inputs: https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#flake-inputs

[anntnzrb]

Fixed

I've implemented the performance optimization suggested in this issue.

Changes Made

Replaced all ./ path references with self flake input in flake.nix:

• Line 17: Updated outputs signature to outputs = { self, ... }@inputs:
• Line 24: src = self; in core-inputs
• Lines 75-76: root = self; and src = self; in snowfall config
• Line 88: src = self; in internal-lib

Verification

✅ nix flake check passes
✅ nix eval .#mkFlake evaluates without warnings
✅ All flake outputs remain intact

This eliminates the performance warning and improves Nix evaluation speed by using the cached flake source instead of re-copying to the store.

Commit: anntnzrb/snowfall-lib@3f738f0