imp Ecosystem

The imp ecosystem provides directory-based configuration for Nix flakes:

imp.lib - Directory imports and tree building for flake-parts
imp.gits - Multi-repo file injection via sparse checkout

Core Workflow

Project Structure

my-project/
├── .imp/
│   └── gits/
│       └── config.nix       # imp.gits injection config
├── nix/
│   └── outputs/
│       └── perSystem/
│           ├── packages.d/
│           │   ├── 00-core.nix      # Your packages
│           │   └── 10-injected.nix  # From injection
│           ├── devShells.nix        # Your devShell
│           └── devShells.d/
│               └── 10-injected.nix  # Injected devShell
└── flake.nix

imp.lib: Directory → Attrset

imp.lib converts directory structures into nested attrsets:

nix

# flake.nix
{
  inputs.imp.url = "github:imp-nix/imp.lib";
  outputs = { imp, ... }:
    imp ./nix/outputs;  # imports everything under nix/outputs/
}

Naming rules:

Path	Attribute
`foo.nix`	`foo`
`foo/default.nix`	`foo`
`foo_.nix`	`foo` (escapes reserved names)
`_foo.nix`	ignored
`foo.d/`	merged fragments

imp.gits: Multi-Repo Injection

Inject files from other repos into your workspace:

nix

# .imp/gits/config.nix
{
  injections = [
    {
      name = "lintfra";
      remote = "https://github.com/org/lintfra.git";
      use = [
        "lint/ast-rules"
        "nix/outputs/perSystem/packages.d/10-lint.nix"
        "nix/outputs/perSystem/devShells.d/10-lintfra.nix"
      ];
    }
  ];
}

Commands:

bash

imp-gits init              # Clone and setup injections
imp-gits pull              # Update injections
imp-gits pull --force      # Force update (overwrites local changes to injected files)
imp-gits status            # Show injection status
eval "$(imp-gits use X)"   # Switch git context to injection X

Fragment Directories (.d pattern)

Auto-merged outputs

These .d directories are auto-merged by imp.lib's tree:

packages.d/, devShells.d/, checks.d/, apps.d/
overlays.d/, nixosModules.d/, homeModules.d/, darwinModules.d/
nixosConfigurations.d/, darwinConfigurations.d/, homeConfigurations.d/

Files sorted by name (00 before 10), merged with lib.recursiveUpdate.

Base + fragments merge: If both foo.nix and foo.d/ exist, they merge:

packages.nix          # { default = myPkg; }
packages.d/
  10-extra.nix        # { lint = lintPkg; }
# Result: { default = myPkg; lint = lintPkg; }

Manual fragment directories

Other .d dirs (e.g., shellHook.d/) are consumed via imp.fragments:

nix

{ imp, ... }:
let
  hooks = imp.fragments ./shellHook.d;  # collects .sh files
in
{
  shellHook = hooks.asString;  # concatenated
}

Common Patterns

Composable devShells (injection pattern)

Injected library provides (devShells.d/10-lintfra.nix):

nix

{ pkgs, self', ... }:
{
  lintfra = pkgs.mkShell {
    packages = [ pkgs.ast-grep self'.packages.lint ];
    shellHook = "echo 'Lint available'";
  };
}

Consumer uses (devShells.nix):

nix

{ pkgs, self', ... }:
{
  default = pkgs.mkShell {
    inputsFrom = [ self'.devShells.lintfra ];  # compose!
    packages = [ /* your packages */ ];
  };
}

Injected packages

Injected (packages.d/10-lint.nix):

nix

{ pkgs, ... }:
{ lint = pkgs.writeShellScriptBin "lint" "..."; }

Result: self'.packages.lint available automatically.

File-level inputs

Declare flake inputs at file level with __inputs:

nix

{
  __inputs = {
    rust-overlay.url = "github:oxalica/rust-overlay";
  };
  __functor = _: { pkgs, rust-overlay, ... }:
    { default = pkgs.rust-bin.stable.latest.default; };
}

Troubleshooting

"attribute X missing"

Check if .d/ file returns correct attrset shape
Verify imp-gits pull synced the file
Run nix flake check for detailed errors

imp-gits pull deletes local files

Only happens with --force on files not in injection's use list
Fixed in imp.gits 0.2.1+ - update your flake

Conflict: foo.nix and foo.d/ both exist

This is allowed for mergeable outputs (packages.d, devShells.d, etc.)
Base file imports first, then fragments merge on top

References

fragment-directories.md - Full .d pattern documentation
gits-workflow.md - imp.gits commands and workflows

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