Add a version option

Cargo.toml

@@ -4,7 +4,7 @@ name = "rustfmt-nightly"
 version = "1.0.0"
 authors = ["Nicholas Cameron <ncameron@mozilla.com>", "The Rustfmt developers"]
 description = "Tool to find and fix Rust formatting issues"
-repository = "https://github.com/rust-lang-nursery/rustfmt"
+repository = "https://github.com/rust-lang/rustfmt"
 readme = "README.md"
 license = "Apache-2.0/MIT"
 build = "build.rs"

Configurations.md

@@ -2367,6 +2367,22 @@ If you want to format code that requires edition 2018, add the following to your
 edition = "2018"
 ```
 
+## `version`
+
+Which version of the formatting rules to use. `Version::One` is backwards-compatible
+with Rustfmt 1.0. Other versions are only backwards compatible within a major
+version number.
+
+- **Default value**: `One`
+- **Possible values**: `One`, `Two`
+- **Stable**: No
+
+### Example
+
+```toml
+version = "Two"
+```
+
 ## `normalize_doc_attributes`
 
 Convert `#![doc]` and `#[doc]` attributes to `//!` and `///` doc comments.

Contributing.md

@@ -2,8 +2,8 @@
 
 There are many ways to contribute to Rustfmt. This document lays out what they
 are and has information for how to get started. If you have any questions about
-contributing or need help with anything, please ping nrc on irc, #rust-dev-tools
+contributing or need help with anything, please ask in the WG-Rustfmt channel
-on irc.mozilla.org is probably the best channel. Feel free to also ask questions
+on [Discord](https://discordapp.com/invite/rust-lang). Feel free to also ask questions
 on issues, or file new issues specifically to get help.
 
 All contributors are expected to follow our [Code of
@@ -14,14 +14,6 @@ Conduct](CODE_OF_CONDUCT.md).
 It would be really useful to have people use rustfmt on their projects and file
 issues where it does something you don't expect.
 
-A really useful thing to do that on a crate from the Rust repo. If it does
-something unexpected, file an issue; if not, make a PR to the Rust repo with the
-reformatted code. We hope to get the whole repo consistently rustfmt'ed and to
-replace `make tidy` with rustfmt as a medium-term goal. Issues with stack traces
-for bugs and/or minimal test cases are especially useful.
-
-See this [blog post](http://ncameron.org/blog/rustfmt-ing-rust/) for more details.
-
 
 ## Create test cases
 
@@ -66,11 +58,14 @@ example, the `issue-1111.rs` test file is configured by the file
 
 ## Debugging
 
-Some `rewrite_*` methods use the `debug!` macro for printing useful information. These messages can be printed by using the environment variable `RUST_LOG=rustfmt=DEBUG`. These traces can be helpful in understanding which part of the code was used and get a better grasp on the execution flow.
+Some `rewrite_*` methods use the `debug!` macro for printing useful information.
+These messages can be printed by using the environment variable `RUST_LOG=rustfmt=DEBUG`.
+These traces can be helpful in understanding which part of the code was used
+and get a better grasp on the execution flow.
 
 ## Hack!
 
-Here are some [good starting issues](https://github.com/rust-lang-nursery/rustfmt/issues?q=is%3Aopen+is%3Aissue+label%3Agood-first-issue).
+Here are some [good starting issues](https://github.com/rust-lang/rustfmt/issues?q=is%3Aopen+is%3Aissue+label%3Agood-first-issue).
 
 If you've found areas which need polish and don't have issues, please submit a
 PR, don't feel there needs to be an issue.
@@ -86,6 +81,12 @@ Talking of tests, if you add a new feature or fix a bug, please also add a test.
 It's really easy, see above for details. Please run `cargo test` before
 submitting a PR to ensure your patch passes all tests, it's pretty quick.
 
+Rustfmt is post-1.0 and within major version releases we strive for backwards
+compatibility (at least when using the default options). That means any code
+which changes Rustfmt's output must be guarded by either an option or a version
+check. The latter is implemented as an option called `option`. See the section on
+[configuration](#Configuration) below.
+
 Please try to avoid leaving `TODO`s in the code. There are a few around, but I
 wish there weren't. You can leave `FIXME`s, preferably with an issue number.
 

README.md

@@ -1,4 +1,4 @@
-# rustfmt [![Build Status](https://travis-ci.org/rust-lang-nursery/rustfmt.svg)](https://travis-ci.org/rust-lang-nursery/rustfmt) [![Build Status](https://ci.appveyor.com/api/projects/status/github/rust-lang-nursery/rustfmt?svg=true)](https://ci.appveyor.com/project/nrc/rustfmt) [![crates.io](https://img.shields.io/crates/v/rustfmt-nightly.svg)](https://crates.io/crates/rustfmt-nightly) [![Travis Configuration Status](https://img.shields.io/travis/davidalber/rustfmt-travis.svg?label=travis%20example)](https://travis-ci.org/davidalber/rustfmt-travis)
+# rustfmt [![Build Status](https://travis-ci.org/rust-lang/rustfmt.svg)](https://travis-ci.org/rust-lang/rustfmt) [![Build Status](https://ci.appveyor.com/api/projects/status/github/rust-lang/rustfmt?svg=true)](https://ci.appveyor.com/project/nrc/rustfmt) [![crates.io](https://img.shields.io/crates/v/rustfmt-nightly.svg)](https://crates.io/crates/rustfmt-nightly) [![Travis Configuration Status](https://img.shields.io/travis/davidalber/rustfmt-travis.svg?label=travis%20example)](https://travis-ci.org/davidalber/rustfmt-travis)
 
 A tool for formatting Rust code according to style guidelines.
 

src/config/mod.rs

@@ -113,6 +113,7 @@ create_config! {
     blank_lines_lower_bound: usize, 0, false,
         "Minimum number of blank lines which must be put between items";
     edition: Edition, Edition::Edition2015, true, "The edition of the parser (RFC 2052)";
+    version: Version, Version::One, false, "Version of formatting rules";
 
     // Options that can change the source code beyond whitespace/blocks (somewhat linty things)
     merge_derives: bool, true, true, "Merge multiple `#[derive(...)]` into a single one";

src/config/options.rs

@@ -291,6 +291,13 @@ configuration_option_enum! { Color:
     Auto,
 }
 
+configuration_option_enum! { Version:
+    // 1.x.y
+    One,
+    // 2.x.y
+    Two,
+}
+
 impl Color {
     /// Whether we should use a coloured terminal.
     pub fn use_colored_tty(self) -> bool {

tests/target/configs/combine_control_expr/false.rs

@@ -1,6 +1,6 @@
 // rustfmt-indent_style: Block
 // rustfmt-combine_control_expr: false
-// Combining openings and closings. See https://github.com/rust-lang-nursery/fmt-rfcs/issues/61.
+// Combining openings and closings. See https://github.com/rust-lang/fmt-rfcs/issues/61.
 
 fn main() {
     // Call

tests/target/configs/combine_control_expr/true.rs

@@ -1,6 +1,6 @@
 // rustfmt-indent_style: Block
 // rustfmt-combine_control_expr: true
-// Combining openings and closings. See https://github.com/rust-lang-nursery/fmt-rfcs/issues/61.
+// Combining openings and closings. See https://github.com/rust-lang/fmt-rfcs/issues/61.
 
 fn main() {
     // Call