Clarify the licensing

CONTRIBUTING.md

@@ -68,6 +68,15 @@ If you're confused about this, don't worry too much about it, if you enable
 "Allow edits by maintainers" we can fix it for you.
 
 
+## Licensing
+
+When contributing, you agree to license your work under the trio
+`Zlib OR Apache-2.0 OR MIT` license (regardless of what the crate's current
+license is).
+
+See also [the license document](./LICENSE.md).
+
+
 ## Release checklist
 
 Copy and fill out the following checklist into the release PR:

Cargo.toml

@@ -16,8 +16,9 @@ repository = "https://github.com/madsmtm/objc2"
 
 # Remember to update in header-translator, and manually authored lib.rs.
 version = "0.2.2"
-# Some crates in this repo may have a different license, see each crate for the specifics.
+# Some crates in this repo have a different license, see LICENSE.md.
 license = "Zlib OR Apache-2.0 OR MIT"
+license-file = "LICENSE.md"
 categories = [
     "api-bindings",
     "development-tools::ffi",

LICENSE.md

@@ -0,0 +1,36 @@
+# License
+
+The licensing of these crates is a bit complicated:
+- The crates `objc2`, `block2`, `objc2-foundation` and `objc2-encode` are
+  [currently][#23] licensed under [the MIT license][MIT].
+- The `dispatch2` crate is dual-licensed under the [Apache-2.0] or [MIT]
+  license, at your option.
+- All other crates are trio-licensed under the [Zlib], [Apache-2.0] or [MIT]
+  license, at your option.
+
+Furthermore, the crates are (usually automatically) derived from Apple SDKs,
+and that may have implications for licensing, see below for details.
+
+[#23]: https://github.com/madsmtm/objc2/issues/23
+[MIT]: https://opensource.org/license/MIT
+[Zlib]: https://zlib.net/zlib_license.html
+[Apache-2.0]: https://www.apache.org/licenses/LICENSE-2.0
+
+
+## Apple SDKs
+
+These crates are derived from Apple SDKs shipped with Xcode. You can obtain a
+copy of the Xcode license at:
+
+https://www.apple.com/legal/sla/docs/xcode.pdf
+
+Or by typing `xcodebuild -license` in your terminal.
+
+From reading the license, it is unclear whether distributing derived works
+such as these crates are allowed?
+
+But in any case, to practically use these crates, you will have to link, and
+that only works when you have the correct Xcode SDK available to provide the
+required `.tbd` files, which is why we choose to still use the normal SPDX
+identifiers in the crates (Xcode is required to use the crates, and when using
+Xcode you have already agreed to the Xcode license).

README.md

@@ -124,13 +124,8 @@ changelog. And so on, with every following release.
 
 ## License
 
-This project is licensed under the MIT license, see [`LICENSE.txt`].
-
-Work is in progress to make it dual-licensed under the Apache License
-(Version 2.0) as well, see [this][#23].
-
-[`LICENSE.txt`]: https://github.com/madsmtm/objc2/blob/master/LICENSE.txt
-[#23]: https://github.com/madsmtm/objc2/issues/23
+The licensing of the project is a bit complicated, see
+[`LICENSE.md`](./LICENSE.md) for details.
 
 
 ## Acknowledgements / Prior art

crates/block2/Cargo.toml

@@ -13,7 +13,9 @@ authors.workspace = true
 edition.workspace = true
 rust-version.workspace = true
 repository.workspace = true
-license = "MIT" # https://github.com/madsmtm/objc2/issues/23
+# https://github.com/madsmtm/objc2/issues/23
+# All future contributions are licensed under "Zlib OR Apache-2.0 OR MIT".
+license = "MIT"
 
 [lints]
 workspace = true

crates/header-translator/Cargo.toml

@@ -4,7 +4,7 @@ version = "0.1.0"
 edition.workspace = true
 publish = false
 repository.workspace = true
-license = "Zlib OR Apache-2.0 OR MIT"
+license.workspace = true
 
 [dependencies]
 # https://github.com/KyleMayes/clang-rs/pull/58

crates/objc2-encode/Cargo.toml

@@ -9,7 +9,9 @@ categories = [
     "no-std",
     "os::macos-apis",
 ]
-license = "MIT" # https://github.com/madsmtm/objc2/issues/23
+# https://github.com/madsmtm/objc2/issues/23
+# All future contributions are licensed under "Zlib OR Apache-2.0 OR MIT".
+license = "MIT"
 authors.workspace = true
 edition.workspace = true
 rust-version.workspace = true

crates/objc2-exception-helper/Cargo.toml

@@ -13,7 +13,7 @@ authors.workspace = true
 edition.workspace = true
 rust-version.workspace = true
 repository.workspace = true
-license = "Zlib OR Apache-2.0 OR MIT"
+license.workspace = true
 
 # Use the `links` key to ensure that only one of these symbols are compiled
 #

crates/objc2-proc-macros/Cargo.toml

@@ -12,7 +12,7 @@ categories = [
 edition.workspace = true
 rust-version.workspace = true
 repository.workspace = true
-license = "Zlib OR Apache-2.0 OR MIT"
+license.workspace = true
 
 [lib]
 proc-macro = true

crates/objc2/Cargo.toml

@@ -10,7 +10,9 @@ categories = [
     "os::macos-apis",
     # "no-std", # TODO
 ]
-license = "MIT" # https://github.com/madsmtm/objc2/issues/23
+# https://github.com/madsmtm/objc2/issues/23
+# All future contributions are licensed under "Zlib OR Apache-2.0 OR MIT".
+license = "MIT"
 authors.workspace = true
 edition.workspace = true
 rust-version.workspace = true

crates/test-assembly/Cargo.toml

@@ -4,7 +4,7 @@ version = "0.1.0"
 edition.workspace = true
 publish = false
 repository.workspace = true
-license = "Zlib OR Apache-2.0 OR MIT"
+license.workspace = true
 
 build = "build.rs"
 

crates/test-ui/Cargo.toml

@@ -3,7 +3,7 @@ name = "test-ui"
 version = "0.1.0"
 edition.workspace = true
 publish = false
-license = "Zlib OR Apache-2.0 OR MIT"
+license.workspace = true
 
 [lints]
 workspace = true

framework-crates/objc2-foundation/Cargo.modified.toml

@@ -1,5 +1,6 @@
 [package]
-license = "MIT" # https://github.com/madsmtm/objc2/issues/23
+# https://github.com/madsmtm/objc2/issues/23
+license = "MIT" # All future contributions are licensed under "Zlib OR Apache-2.0 OR MIT".
 
 [dev-dependencies]
 static_assertions = "1.1.0"

framework-crates/objc2-metal/Cargo.modified.toml

@@ -1,6 +1,3 @@
-[package]
-license = "MIT OR Apache-2.0" # Some code taken from `metal` crate
-
 [[example]]
 name = "triangle"
 required-features = [