117 lines
3.7 KiB
Markdown
117 lines
3.7 KiB
Markdown
# License Guidelines
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We only accept formulae that use a [Debian Free Software Guidelines license](https://wiki.debian.org/DFSGLicenses) or are released into the public domain following [DFSG Guidelines on Public Domain software](https://wiki.debian.org/DFSGLicenses#Public_Domain).
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## Specifying a License
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All licenses are identified by their license identifier from the [SPDX License List](https://spdx.org/licenses/).
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Specify a license by passing it to the `license` method:
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```ruby
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license "MIT"
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```
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The public domain can be indicated using a symbol:
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```ruby
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license :public_domain
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```
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If the license for a formula cannot be represented using an SPDX expression:
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```ruby
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license :cannot_represent
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```
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## Complex SPDX License Expressions
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Some formulae have multiple licenses that need to be combined in different ways. In these cases, a more complex license expression can be used. These expressions are based on the [SPDX License Expression Guidelines](https://spdx.github.io/spdx-spec/appendix-IV-SPDX-license-expressions/).
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Add a `+` to indicate that the user can choose a later version of the same license:
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```ruby
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license "EPL-1.0+"
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```
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GNU licenses (`GPL`, `LGPL`, `AGPL` and `GFDL`) require either the `-only` or the `-or-later` suffix to indicate whether a later version of the license is allowed:
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```ruby
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license "LGPL-2.1-only"
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```
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```ruby
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license "GPL-1.0-or-later"
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```
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Use `:any_of` to indicate that the user can choose which license applies:
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```ruby
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license any_of: ["MIT", "0BSD"]
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```
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Use `:all_of` to indicate that the user must comply with multiple licenses:
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```ruby
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license all_of: ["MIT", "0BSD"]
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```
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Use `:with` to indicate a license exception:
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```ruby
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license "MIT" => { with: "LLVM-exception" }
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```
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These expressions can be nested as needed:
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```ruby
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license any_of: [
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"MIT",
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:public_domain,
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all_of: ["0BSD", "Zlib", "Artistic-1.0+"],
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"Apache-2.0" => { with: "LLVM-exception" },
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]
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```
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## Specifying Forbidden Licenses
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The `HOMEBREW_FORBIDDEN_LICENSES` environment variable can be set to forbid installation of formulae that require or have dependencies that require certain licenses.
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The `HOMEBREW_FORBIDDEN_LICENSES` should be set to a space separated list of licenses. Use `public_domain` to forbid installation of formulae with a `:public_domain` license.
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For example, the following forbids installation of `MIT`, `Artistic-1.0` and `:public_domain` licenses:
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```bash
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export HOMEBREW_FORBIDDEN_LICENSES="MIT Artistic-1.0 public_domain"
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```
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In this example Homebrew would refuse to install any formula that specifies the `MIT` license. Homebrew would also forbid installation of any formula that declares a dependency on a formula that specifies `MIT`, even if the original formula has an allowed license.
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Homebrew interprets complex license expressions and determines whether the licenses allow installation. To continue the above example, Homebrew would not allow installation of a formula with the following license declarations:
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```ruby
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license any_of: ["MIT", "Artistic-1.0"]
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```
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```ruby
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license all_of: ["MIT", "0BSD"]
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```
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Homebrew _would_ allow formulae with the following declaration to be installed:
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```ruby
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license any_of: ["MIT", "0BSD"]
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```
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`HOMEBREW_FORBIDDEN_LICENSES` can also forbid future versions of specific licenses. For example, to forbid `Artistic-1.0`, `Artistic-2.0` and any future Artistic licenses, use:
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```bash
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export HOMEBREW_FORBIDDEN_LICENSES="Artistic-1.0+"
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```
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For GNU licenses (such as `GPL`, `LGPL`, `AGPL` and `GFDL`), use `-only` or `-or-later`. For example, the following would forbid `GPL-2.0`, `LGPL-2.1` and `LGPL-3.0` formulae from being installed, but would allow `GPL-3.0`
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```bash
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export HOMEBREW_FORBIDDEN_LICENSES="GPL-2.0-only LGPL-2.1-or-later"
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```
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