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directories-next 2.0.0

A tiny mid-level library that provides platform-specific standard locations of directories for config, cache and other data on Linux, Windows and macOS by leveraging the mechanisms defined by the XDG base/user directory specifications on Linux, the Known Folder API on Windows, and the Standard Directory guidelines on macOS.
Documentation
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# `directories-next`

**NOTE**: This crate is a fork of once-abandoned `directories` crate.

There is a low-level sister library, [dirs-next].

## Introduction

- a tiny mid-level library with a minimal API
- that provides the platform-specific, user-accessible locations
- for retrieving and storing configuration, cache and other data
- on Linux, Redox, Windows (≥ Vista), macOS and other platforms.

The library provides the location of these directories by leveraging the mechanisms defined by
- the [XDG base directory]https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html and
  the [XDG user directory]https://www.freedesktop.org/wiki/Software/xdg-user-dirs/ specifications on Linux
- the [Known Folder]https://msdn.microsoft.com/en-us/library/windows/desktop/dd378457.aspx API on Windows
- the [Standard Directories]https://developer.apple.com/library/content/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/FileSystemOverview/FileSystemOverview.html#//apple_ref/doc/uid/TP40010672-CH2-SW6
  guidelines on macOS

## Platforms

This library is written in Rust, and supports Linux, Redox, macOS and Windows.
Other platforms are also supported; they use the Linux conventions.

## Minimum Rust version policy

The minimal required version of Rust is `1.34.0`.

We may bump the Rust version in major and minor releases (`x`/`y` in `x.y.z`).
Changing the Rust version will be written in the CHANGELOG.

## Example

Library run by user Alice:

```rust
use directories_next::{BaseDirs, UserDirs, ProjectDirs};

if let Some(proj_dirs) = ProjectDirs::from("com", "Foo Corp",  "Bar App") {
    proj_dirs.config_dir();
    // Lin: /home/alice/.config/barapp
    // Win: C:\Users\Alice\AppData\Roaming\Foo Corp\Bar App\config
    // Mac: /Users/Alice/Library/Application Support/com.Foo-Corp.Bar-App
}

if let Some(base_dirs) = BaseDirs::new() {
    base_dirs.executable_dir();
    // Lin: Some(/home/alice/.local/bin)
    // Win: None
    // Mac: None
}

if let Some(user_dirs) = UserDirs::new() {
    user_dirs.audio_dir();
    // Lin: /home/alice/Music
    // Win: C:\Users\Alice\Music
    // Mac: /Users/Alice/Music
}
```

## Design Goals

- The _directories-next_ library is designed to provide an accurate snapshot of the system's state at
  the point of invocation of `BaseDirs::new`, `UserDirs::new` or `ProjectDirs::from`. Subsequent
  changes to the state of the system are not reflected in values created prior to such a change.
- This library does not create directories or check for their existence. The library only provides
  information on what the path to a certain directory _should_ be. How this information is used is
  a decision that developers need to make based on the requirements of each individual application.
- This library is intentionally focused on providing information on user-writable directories only.
  There is no discernible benefit in returning a path that points to a user-level, writable
  directory on one operating system, but a system-level, read-only directory on another, that would
  outweigh the confusion and unexpected failures such an approach would cause.
  - `executable_dir` is specified to provide the path to a user-writable directory for binaries.<br/>
    As such a directory only commonly exists on Linux, it returns `None` on macOS and Windows.
  - `font_dir` is specified to provide the path to a user-writable directory for fonts.<br/>
    As such a directory only exists on Linux and macOS, it returns `None` on Windows.
  - `runtime_dir` is specified to provide the path to a directory for non-essential runtime data.
    It is required that this directory is created when the user logs in, is only accessible by the
    user itself, is deleted when the user logs out, and supports all filesystem features of the
    operating system.<br/>
    As such a directory only commonly exists on Linux, it returns `None` on macOS and Windows.

## Features

### `BaseDirs`

The intended use case for `BaseDirs` is to query the paths of user-invisible standard directories
that have been defined according to the conventions of the operating system the library is running on.

If you want to compute the location of cache, config or data directories for your own application
or project, use `ProjectDirs` instead.

| Function name    | Value on Linux                                                                                  | Value on Windows            | Value on macOS                      |
| ---------------- | ----------------------------------------------------------------------------------------------- | --------------------------- | ----------------------------------- |
| `home_dir`       | `$HOME`                                                                                         | `{FOLDERID_Profile}`        | `$HOME`                             |
| `cache_dir`      | `$XDG_CACHE_HOME`              or `$HOME`/.cache                                                | `{FOLDERID_LocalAppData}`   | `$HOME`/Library/Caches              |
| `config_dir`     | `$XDG_CONFIG_HOME`             or `$HOME`/.config                                               | `{FOLDERID_RoamingAppData}` | `$HOME`/Library/Application Support |
| `data_dir`       | `$XDG_DATA_HOME`               or `$HOME`/.local/share                                          | `{FOLDERID_RoamingAppData}` | `$HOME`/Library/Application Support |
| `data_local_dir` | `$XDG_DATA_HOME`               or `$HOME`/.local/share                                          | `{FOLDERID_LocalAppData}`   | `$HOME`/Library/Application Support |
| `executable_dir` | `Some($XDG_BIN_HOME`/../bin`)` or `Some($XDG_DATA_HOME`/../bin`)` or `Some($HOME`/.local/bin`)` | `None`                      | `None`                              |
| `runtime_dir`    | `Some($XDG_RUNTIME_DIR)`       or `None`                                                        | `None`                      | `None`                              |

### `UserDirs`

The intended use case for `UserDirs` is to query the paths of user-facing standard directories
that have been defined according to the conventions of the operating system the library is running on.

| Function name    | Value on Linux                                                         | Value on Windows                 | Value on macOS                 |
| ---------------- | ---------------------------------------------------------------------- | -------------------------------- | ------------------------------ |
| `home_dir`       | `$HOME`                                                                | `{FOLDERID_Profile}`             | `$HOME`                        |
| `audio_dir`      | `Some(XDG_MUSIC_DIR)`           or `None`                              | `Some({FOLDERID_Music})`         | `Some($HOME`/Music/`)`         |
| `desktop_dir`    | `Some(XDG_DESKTOP_DIR)`         or `None`                              | `Some({FOLDERID_Desktop})`       | `Some($HOME`/Desktop/`)`       |
| `document_dir`   | `Some(XDG_DOCUMENTS_DIR)`       or `None`                              | `Some({FOLDERID_Documents})`     | `Some($HOME`/Documents/`)`     |
| `download_dir`   | `Some(XDG_DOWNLOAD_DIR)`        or `None`                              | `Some({FOLDERID_Downloads})`     | `Some($HOME`/Downloads/`)`     |
| `font_dir`       | `Some($XDG_DATA_HOME`/fonts/`)` or `Some($HOME`/.local/share/fonts/`)` | `None`                           | `Some($HOME`/Library/Fonts/`)` |
| `picture_dir`    | `Some(XDG_PICTURES_DIR)`        or `None`                              | `Some({FOLDERID_Pictures})`      | `Some($HOME`/Pictures/`)`      |
| `public_dir`     | `Some(XDG_PUBLICSHARE_DIR)`     or `None`                              | `Some({FOLDERID_Public})`        | `Some($HOME`/Public/`)`        |
| `template_dir`   | `Some(XDG_TEMPLATES_DIR)`       or `None`                              | `Some({FOLDERID_Templates})`     | `None`                         | 
| `video_dir`      | `Some(XDG_VIDEOS_DIR)`          or `None`                              | `Some({FOLDERID_Videos})`        | `Some($HOME`/Movies/`)`        |

### `ProjectDirs`

The intended use case for `ProjectDirs` is to compute the location of cache,
config or data directories for your own application or project,
which are derived from the standard directories.

| Function name    | Value on Linux                                                                     | Value on Windows                                    | Value on macOS                                       |
| ---------------- | ---------------------------------------------------------------------------------- | --------------------------------------------------- | ---------------------------------------------------- |
| `cache_dir`      | `$XDG_CACHE_HOME`/`<project_path>`        or `$HOME`/.cache/`<project_path>`       | `{FOLDERID_LocalAppData}`/`<project_path>`/cache    | `$HOME`/Library/Caches/`<project_path>`              |
| `config_dir`     | `$XDG_CONFIG_HOME`/`<project_path>`       or `$HOME`/.config/`<project_path>`      | `{FOLDERID_RoamingAppData}`/`<project_path>`/config | `$HOME`/Library/Application Support/`<project_path>` |
| `data_dir`       | `$XDG_DATA_HOME`/`<project_path>`         or `$HOME`/.local/share/`<project_path>` | `{FOLDERID_RoamingAppData}`/`<project_path>`/data   | `$HOME`/Library/Application Support/`<project_path>` |
| `data_local_dir` | `$XDG_DATA_HOME`/`<project_path>`         or `$HOME`/.local/share/`<project_path>` | `{FOLDERID_LocalAppData}`/`<project_path>`/data     | `$HOME`/Library/Application Support/`<project_path>` |
| `runtime_dir`    | `Some($XDG_RUNTIME_DIR`/`_project_path_)`                                          | `None`                                              | `None`                                               |

The specific value of `<project_path>` is computed by the

```rust
ProjectDirs::from(qualifier: &str,
                  organization: &str,
                  application: &str)
```

function and varies across operating systems. As an example, calling

```rust
ProjectDirs::from("org"         /*qualifier*/,
                  "Baz Corp"    /*organization*/,
                  "Foo Bar-App" /*application*/)
```

results in the following values:

| Value on Linux | Value on Windows         | Value on macOS               |
| -------------- | ------------------------ | ---------------------------- |
| `"foobar-app"` | `"Baz Corp/Foo Bar-App"` | `"org.Baz-Corp.Foo-Bar-App"` |

The `ProjectDirs::from_path` function allows the creation of `ProjectDirs` structs
directly from a `PathBuf` value.
This argument is used verbatim and is not adapted to operating system standards.
The use of `ProjectDirs::from_path` is strongly discouraged, as its results
will not follow operating system standards on at least two of three platforms.

## Comparison

There are other crates in the Rust ecosystem that try similar or related things.
Here is an overview of them, combined with ratings on properties that guided
the design of this crate.

Please take this table with a grain of salt: a different crate might very well
be more suitable for your specific use case.

| Library               | Status         | Lin | Mac | Win |Base|User|Proj|Conv|
| --------------------- | -------------- |:---:|:---:|:---:|:--:|:--:|:--:|:--:|
| `app_dirs`            | Unmaintained   |||| 🞈  ||||
| `app_dirs2`           | Maintained     |||| 🞈  ||||
| `dirs-next`           | Developed      ||||||||
| **directories-next**  | **Developed**  ||||||||
| `s_app_dir`           | Unmaintained?  |||  🞈  ||| 🞈  ||
| `standard_paths`      | Maintained     ||||||||
| `xdg`                 | Maintained     ||||||| 🞈  |
| `xdg-basedir`         | Unmaintained?  ||||||| 🞈  |
| `xdg-rs`              | Obsolete       ||||||| 🞈  |

- Lin: Linux support
- Mac: macOS support
- Win: Windows support
- Base: Supports [generic base directories]#basedirs
- User: Supports [user directories]#userdirs
- Proj: Supports [project-specific base directories]#projectdirs
- Conv: Follows naming conventions of the operating system it runs on

## Build

It's possible to cross-compile this library if the necessary toolchains are installed with rustup.
This is helpful to ensure a change has not broken compilation on a different platform.

The following commands will build this library on Linux, macOS and Windows:

```console
cargo build --target=x86_64-unknown-linux-gnu
cargo build --target=x86_64-pc-windows-gnu
cargo build --target=x86_64-apple-darwin
cargo build --target=x86_64-unknown-redox
```

## License

Licensed under either of

 * Apache License, Version 2.0
   ([LICENSE-APACHE]LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
 * MIT license
   ([LICENSE-MIT]LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

## Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.

[dirs-next]: https://github.com/xdg-rs/dirs