Relicense Bevy under the dual MIT or Apache-2.0 license (#2509)

This relicenses Bevy under the dual MIT or Apache-2.0 license. For rationale, see #2373.

* Changes the LICENSE file to describe the dual license. Moved the MIT license to docs/LICENSE-MIT. Added the Apache-2.0 license to docs/LICENSE-APACHE. I opted for this approach over dumping both license files at the root (the more common approach) for a number of reasons:
  * Github links to the "first" license file (LICENSE-APACHE) in its license links (you can see this in the wgpu and rust-analyzer repos). People clicking these links might erroneously think that the apache license is the only option. Rust and Amethyst both use COPYRIGHT or COPYING files to solve this problem, but this creates more file noise (if you do everything at the root) and the naming feels way less intuitive. 
  * People have a reflex to look for a LICENSE file. By providing a single license file at the root, we make it easy for them to understand our licensing approach. 
  * I like keeping the root clean and noise free
  * There is precedent for putting the apache and mit license text in sub folders (amethyst) 
* Removed the `Copyright (c) 2020 Carter Anderson` copyright notice from the MIT license. I don't care about this attribution, it might make license compliance more difficult in some cases, and it didn't properly attribute other contributors. We shoudn't replace it with something like "Copyright (c) 2021 Bevy Contributors" because "Bevy Contributors" is not a legal entity. Instead, we just won't include the copyright line (which has precedent ... Rust also uses this approach).
* Updates crates to use the new "MIT OR Apache-2.0" license value
* Removes the old legion-transform license file from bevy_transform. bevy_transform has been its own, fully custom implementation for a long time and that license no longer applies.
* Added a License section to the main readme
* Updated our Bevy Plugin licensing guidelines.

As a follow-up we should update the website to properly describe the new license.

Closes #2373

.github/label-config.yml

@@ -3,6 +3,3 @@
 
 S-Needs-Triage:
 - "**"
-
-S-Pre-Relicense:
-- "**"

Cargo.toml

@@ -11,7 +11,7 @@ description = "A refreshingly simple data-driven game engine and app framework"
 exclude = ["assets/**/*", "tools/**/*", ".github/**/*", "crates/**/*"]
 homepage = "https://bevyengine.org"
 keywords = ["game", "engine", "gamedev", "graphics", "bevy"]
-license = "MIT"
+license = "MIT OR Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/bevyengine/bevy"
 

LICENSE

@@ -1,21 +1,6 @@
-MIT License
+Bevy is dual-licensed under either
 
-Copyright (c) 2020 Carter Anderson
+* MIT License (docs/LICENSE-MIT or http://opensource.org/licenses/MIT)
+* Apache License, Version 2.0 (docs/LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
 
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.
+at your option.

README.md

@@ -1,7 +1,7 @@
 # [![Bevy](assets/branding/bevy_logo_light_dark_and_dimmed.svg)](https://bevyengine.org)
 
 [![Crates.io](https://img.shields.io/crates/v/bevy.svg)](https://crates.io/crates/bevy)
-[![license](https://img.shields.io/badge/license-MIT-blue.svg)](./LICENSE)
+[![MIT/Apache 2.0](https://img.shields.io/badge/license-MIT%2FApache-blue.svg)](./LICENSE)
 [![Crates.io](https://img.shields.io/crates/d/bevy.svg)](https://crates.io/crates/bevy)
 [![Rust](https://github.com/bevyengine/bevy/workflows/CI/badge.svg)](https://github.com/bevyengine/bevy/actions)
 ![iOS cron CI](https://github.com/bevyengine/bevy/workflows/iOS%20cron%20CI/badge.svg)
@@ -98,3 +98,16 @@ Plugins are very welcome to extend Bevy's features. [Guidelines][plugin_guidelin
 ## Thanks and Alternatives
 
 Additionally, we would like to thank the [Amethyst](https://github.com/amethyst/amethyst), [macroquad](https://github.com/not-fl3/macroquad), [coffee](https://github.com/hecrj/coffee), [ggez](https://github.com/ggez/ggez), [rg3d](https://github.com/mrDIMAS/rg3d), and [Piston](https://github.com/PistonDevelopers/piston) projects for providing solid examples of game engine development in Rust. If you are looking for a Rust game engine, it is worth considering all of your options. Each engine has different design goals, and some will likely resonate with you more than others.
+
+## License
+
+Bevy is free and open source! All code in this repository is dual-licensed under either:
+
+* MIT License ([LICENSE-MIT](docs/LICENSE-MIT) or [http://opensource.org/licenses/MIT](http://opensource.org/licenses/MIT))
+* Apache License, Version 2.0 ([LICENSE-APACHE](docs/LICENSE-APACHE) or [http://www.apache.org/licenses/LICENSE-2.0](http://www.apache.org/licenses/LICENSE-2.0))
+
+at your option. This means you can select the license you prefer! This dual-licensing approach is the de-facto standard in the Rust ecosystem and there are [very good reasons](https://github.com/bevyengine/bevy/issues/2373) to include both.
+
+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.

crates/bevy_app/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides core App functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [features]

crates/bevy_asset/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides asset functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [features]

crates/bevy_audio/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides audio functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_core/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides core functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 

crates/bevy_derive/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides derive implementations for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [lib]

crates/bevy_diagnostic/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides diagnostic functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 

crates/bevy_dylib/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Force the Bevy Engine to be dynamically linked for faster linking"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [lib]

crates/bevy_dynamic_plugin/Cargo.toml

@@ -9,7 +9,7 @@ edition = "2018"
 description = "Provides dynamic plugin loading capabilities for non-wasm platforms"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

crates/bevy_ecs/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Bevy Engine's entity component system"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["ecs", "game", "bevy"]
 categories = ["game-engines", "data-structures"]
 

crates/bevy_ecs/macros/Cargo.toml

@@ -7,7 +7,7 @@ authors = [
     "Carter Anderson <mcanders1@gmail.com>",
 ]
 edition = "2018"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 
 [lib]
 proc-macro = true

crates/bevy_gilrs/Cargo.toml

@@ -6,7 +6,7 @@ authors = ["Bevy Contributors <bevyengine@gmail.com>", "Carter Anderson <mcander
 description = "Gamepad system made using Gilrs for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_gltf/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Bevy Engine GLTF loading"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_input/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides input functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [features]

crates/bevy_internal/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "An internal Bevy crate used to facilitate optional dynamic linking via the 'dynamic' feature"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["game", "engine", "gamedev", "graphics", "bevy"]
 categories = ["game-engines", "graphics", "gui", "rendering"]
 

crates/bevy_log/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides logging for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 

crates/bevy_macro_utils/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "A collection of utils for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_math/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides math functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_pbr/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Adds PBR rendering to Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_reflect/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Dynamically interact with rust types"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 readme = "README.md"
 

crates/bevy_reflect/bevy_reflect_derive/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Derive implementations for bevy_reflect"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [lib]

crates/bevy_render/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides rendering functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_scene/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides scene functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_sprite/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides sprite functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_tasks/Cargo.toml

@@ -10,7 +10,7 @@ authors = [
 description = "A task executor for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

crates/bevy_text/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides text functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [features]

crates/bevy_transform/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides hierarchy and transform functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_ui/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "A custom ECS-driven UI framework built specifically for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_utils/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "A collection of utils for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_wgpu/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "A wgpu render backend for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [features]

crates/bevy_window/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "Provides windowing functionality for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [dependencies]

crates/bevy_winit/Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 description = "A winit window and input backend for Bevy Engine"
 homepage = "https://bevyengine.org"
 repository = "https://github.com/bevyengine/bevy"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [features]

docs/LICENSE-APACHE

@@ -0,0 +1,176 @@
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+                        http://www.apache.org/licenses/
+
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+   END OF TERMS AND CONDITIONS

docs/LICENSE-MIT

@@ -1,7 +1,5 @@
 MIT License
 
-Copyright (c) 2019 Alec Thilenius
-
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights

docs/plugins_guidelines.md

@@ -71,7 +71,10 @@ This advice is valid for any Rust crate.
 
 ### Licensing
 
-Rust projects are often dual licensed with [MIT and Apache 2.0](https://www.rust-lang.org/policies/licenses). Bevy is licensed with [MIT](https://github.com/bevyengine/bevy/blob/main/LICENSE). Those are great options to license your plugin.
+Bevy is dual licensed under [MIT or Apache 2.0](https://www.rust-lang.org/policies/licenses), at your option. Most other Rust projects (including Rust itself) also use this dual-license approach. MIT-only is very popular and you might be tempted to just use that (Bevy also used to be MIT-only), but there are [very good reasons](https://github.com/bevyengine/bevy/issues/2373) to include both and we highly recommend using the dual MIT / Apache-2.0 license for your Bevy Plugins and crates:
+
+* Including the Apache 2.0 license option significantly reduces the difficulty and boilerplate of proper license compliance in published games because you only need to include one copy of the Apache 2.0 license.
+* Provides maximum compatibility with Bevy and Rust, making it easier to upstream your changes.
 
 ### Small Crate Size