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Nix, the purely functional package manager
60857de63e
Replaces manual graph traversal in `nix why-depends` with the new
DependencyGraph infrastructure. Simplifies code while maintaining
identical output and behavior.
## Changes to why-depends
**Before**: Custom Node struct with manual Dijkstra implementation
- 150+ lines of graph management boilerplate
- Manual priority queue and distance tracking
- Custom reverse reference bookkeeping
- Inline file scanning mixed with graph traversal
**After**: Clean API calls to DependencyGraph
- Replaced Node struct with DependencyGraph<StorePath>
- Replaced manual Dijkstra with computeDistancesFrom()
- Use getSuccessors() instead of managing refs/rrefs
- Extracted findHashContexts() helper for clarity
**Improvements**:
- ~50 lines shorter, easier to understand
- C++20 ranges for cleaner iteration
- Separated concerns: graph ops vs. file scanning vs. formatting
- Complex algorithms now in well-tested DependencyGraph
## Example Transformation
```cpp
// Before: Manual graph building
std::map<StorePath, Node> graph;
for (auto & path : closure)
graph.emplace(path, Node{...});
for (auto & node : graph)
for (auto & ref : node.second.refs)
graph.find(ref)->second.rrefs.insert(node.first);
// After: Use DependencyGraph API
StorePathGraph depGraph(*store, closure);
depGraph.computeDistancesFrom(dependencyPath);
auto successors = depGraph.getSuccessors(nodePath);
```
## Helper Extraction
**findHashContexts()**: Extracted file scanning into reusable function
- Takes accessor, reference paths, target hash
- Returns hash → formatted context strings
- Keeps printNode() focused on graph traversal
## Test Improvements
**references.cc**: Changed ASSERT_EQ → EXPECT_EQ
- EXPECT continues after failure, shows all results
- Better debugging when multiple assertions fail
- GoogleTest best practice
## Behavior Preservation
**Critical**: Pure refactoring, zero user-visible changes
- Identical output format
- Same algorithm (Dijkstra shortest paths)
- Same filtering/highlighting
- Same CLI interface
## Benefits
1. **Maintainability**: Algorithms in shared, tested infrastructure
2. **Correctness**: DependencyGraph thoroughly unit tested
3. **Reusability**: Other commands can now use DependencyGraph
4. **Readability**: why-depends focused on UI, not graph algorithms
5. **Future-proof**: Sets stage for improved error messages
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|---|---|---|
| .github | ||
| ci/gha | ||
| contrib | ||
| doc/manual | ||
| maintainers | ||
| misc | ||
| nix-meson-build-support | ||
| packaging | ||
| scripts | ||
| src | ||
| tests | ||
| .clang-format | ||
| .clang-tidy | ||
| .dir-locals.el | ||
| .editorconfig | ||
| .git-blame-ignore-revs | ||
| .gitignore | ||
| .shellcheckrc | ||
| .version | ||
| CITATION.cff | ||
| CONTRIBUTING.md | ||
| COPYING | ||
| default.nix | ||
| docker.nix | ||
| flake.lock | ||
| flake.nix | ||
| HACKING.md | ||
| meson.build | ||
| meson.format | ||
| meson.options | ||
| README.md | ||
| shell.nix | ||
Nix
Nix is a powerful package manager for Linux and other Unix systems that makes package management reliable and reproducible. Please refer to the Nix manual for more details.
Installation and first steps
Visit nix.dev for installation instructions and beginner tutorials.
Full reference documentation can be found in the Nix manual.
Building and developing
Follow instructions in the Nix reference manual to set up a development environment and build Nix from source.
Contributing
Check the contributing guide if you want to get involved with developing Nix.
Additional resources
Nix was created by Eelco Dolstra and developed as the subject of his PhD thesis The Purely Functional Software Deployment Model, published 2006. Today, a world-wide developer community contributes to Nix and the ecosystem that has grown around it.
- The Nix, Nixpkgs, NixOS Community on nixos.org
- Official documentation on nix.dev
- Nixpkgs is the largest, most up-to-date free software repository in the world
- NixOS is a Linux distribution that can be configured fully declaratively
- Discourse
- Matrix: #users:nixos.org for user support and #nix-dev:nixos.org for development
License
Nix is released under the LGPL v2.1.