# solvent
Solvent is a dependency resolver library written in rust.

[![Build Status](https://travis-ci.org/mikedilger/solvent.svg?branch=master)](https://travis-ci.org/mikedilger/solvent)
[![MIT licensed](https://img.shields.io/badge/license-MIT-blue.svg)](./LICENSE)

Documentation is available at https://docs.rs/solvent

Solvent helps you to resolve dependency orderings by building up a dependency graph and then
resolving the dependences of some target node in an order such that each output depends only upon
the previous outputs.

It is currently quite simple, but is still useful.

The type of the nodes should be small (as you will pass them) and should implement Eq. References
are good choices.

## Example

```rust
extern crate solvent;

use solvent::DepGraph;

fn main() {
    // Create a new empty DepGraph.
    let mut depgraph: DepGraph<&str> = DepGraph::new();

    // You can register a dependency like this.  Solvent will automatically create nodes for any
    // term it has not seen before.  This means 'b' depends on 'd'
    depgraph.register_dependency("b","d");

    // You can also register multiple dependencies at once
    depgraph.register_dependencies("a",vec!["b","c","d"]);
    depgraph.register_dependencies("c",vec!["e"]);

    // Iterate through each dependency of "a".  The dependencies will be returned in an order such
    // that each output only depends on the previous outputs (or nothing).  The target itself will
    // be output last.
    for node in depgraph.dependencies_of(&"a").unwrap() {
        print!("{} ", node.unwrap());
    }
}
```

The above will output:  `d b e c a` or `e c d b a` or some other valid dependency order.

The algorithm is not deterministic, and may give a different answer each time it is run.

The iterator dependencies_of() returns an `Option<Result<T, SolventError>>`.  The for loop
handles the `Option` part for you, but you may want to check the result for `SolventError`.  Once
an error is returned, all subsequent calls to the iterator `next()` will yield `None`.

You can also mark some elements as already satisfied, and the iterator will take that into account:

```ignore
depgraph.mark_as_satisfied(["e","c"]).unwrap();
```

Dependency cycles are detected and will return `SolventError::CycleDetected`.

## Use Cases
These kinds of calculations are useful in the following example situations:
* System package management: packages depending on other packages
* Build systems such as 'make' or 'cargo' to handle dependencies (note: neither cargo nor rustc use
  solvent)
* Complex software configurations such as Linux kernel configurations
* Database schema upgrades which don't need to be strictly sequential (e.g. multiple developers
  working on separate git branches being able to commit database schema upgrades independently,
  without merge conflicts) -- the author wrote solvent for this purpose.

This crate is NOT a SAT solver, it is much simpler.

## Other Details
Solvent does not yet handle boolean logic.  See issue [#1]
(https://github.com/mikedilger/solvent/issues/1).