-# rustfmt
+# rustfmt [](https://travis-ci.org/rust-lang-nursery/rustfmt)
A tool for formatting Rust code according to style guidelines.
+If you'd like to help out (and you should, it's a fun project!), see
+[Contributing.md](Contributing.md).
-## How to use
+## Quick start
-`cargo build` to build.
-
-`cargo test` to run all tests.
-
-`cargo run filename` to run on a file, if the file includes out of line modules,
-then we reformat those too. So to run on a whole module or crate, you just need
-to run on the top file. You'll probably want to set the `WriteMode` in the call
-to `run` in `main()`. Eventually you should be able to set the mode from the
-command line or from a config file or something.
-
-You'll need a pretty up to date version of the nightly version of Rust.
-
-## Use cases
-
-A formatting tool can be used in different ways and the different use cases can
-affect the design of the tool. The use cases I'm particularly concerned with are:
-
-* running on a whole repo before check-in
- - in particular, to replace the `make tidy` pass on the Rust distro
-* running on code from another project that you are adding to your own
-* using for mass changes in code style over a project
-
-Some valid use cases for a formatting tool which I am explicitly not trying to
-address (although it would be nice, if possible):
-
-* running 'as you type' in an IDE
-* running on arbitrary snippets of code
-* running on Rust-like code, specifically code which doesn't parse
-* use as a pretty printer inside the compiler
-* refactoring
-* formatting totally unformatted source code
-
-
-## Scope and vision
-
-I do not subscribe to the notion that a formatting tool should only change
-whitespace. I believe that we should semantics preserving, but not necessarily
-syntax preserving, i.e., we can change the AST of a program.
-
-I.e., we might change glob imports to list or single imports, re-order imports,
-move bounds to where clauses, combine multiple impls into a single impl, etc.
-
-However, we will not change the names of variables or make any changes which
-*could* change the semantics. To be ever so slightly formal, we might imagine
-a compilers high level intermediate representation, we should strive to only
-make changes which do not change the HIR, even if they do change the AST.
-
-I would like to be able to output refactoring scripts for making deeper changes
-though. (E.g., renaming variables to satisfy our style guidelines).
-
-My long term goal is that all style lints can be moved from the compiler to
-rustfmt and, as well as warning, can either fix problems or emit refactoring
-scripts to do so.
-
-### Configurability
-
-I believe reformatting should be configurable to some extent. We should read in
-options from a configuration file and reformat accordingly. We should supply at
-least a config file which matches the Rust style guidelines.
-
-There should be multiple modes for running the tool. As well as simply replacing
-each file, we should be able to show the user a list of the changes we would
-make, or show a list of violations without corrections (the difference being
-that there are multiple ways to satisfy a given set of style guidelines, and we
-should distinguish violations from deviations from our own model).
-
-
-## Implementation philosophy
-
-Some details of the philosophy behind the implementation.
+To install:
+```
+cargo install rustfmt
+```
-### Operate on the AST
+to run on a cargo project in the current working directory:
-A reformatting tool can be based on either the AST or a token stream (in Rust
-this is actually a stream of token trees, but its not a fundamental difference).
-There are pros and cons to the two approaches. I have chosen to use the AST
-approach. The primary reasons are that it allows us to do more sophisticated
-manipulations, rather than just change whitespace, and it gives us more context
-when making those changes.
+```
+cargo fmt
+```
-The advantage of the tokens approach are that you can operate on non-parsable
-code. I don't care too much about that, it would be nice, but I think being able
-to sophisticated transformations is more important. In the future I hope to
-(optionally) be able to use type information for informing reformatting too. One
-specific case of unparsable code is macros. Using tokens is certainly easier
-here, but I believe it is perfectly solvable with the AST approach. At the limit,
-we can operate on just tokens in the macro case.
+## Installation
-I believe that there is not in fact that much difference between the two
-approaches. Due to imperfect span information, under the AST approach, we
-sometimes are reduced to examining tokens or do some re-lexing of our own. Under
-the tokens approach you need to implement your own (much simpler) parser. I
-believe that as the tool gets more sophisticated, you end up doing more at the
-token-level, or having an increasingly sophisticated parser, until at the limit
-you have the same tool.
+> **Note:** this method currently requires you to be running cargo 0.6.0 or
+> newer.
-However, I believe starting from the AST gets you more quickly to a usable and
-useful tool.
+```
+cargo install rustfmt
+```
+or if you're using [`multirust`](https://github.com/brson/multirust)
-### Heuristic rather than algorithmic
+```
+multirust run nightly cargo install rustfmt
+```
-Many formatting tools use a very general algorithmic or even algebraic tool for
-pretty printing. This results in very elegant code, but I believe does not give
-the best results. I prefer a more ad hoc approach where each expression/item is
-formatted using custom rules. We hopefully don't end up with too much code due
-to good old fashioned abstraction and code sharing. This will give a bigger code
-base, but hopefully a better result.
+Usually cargo-fmt, which enables usage of Cargo subcommand `cargo fmt`, is
+installed alongside rustfmt. To only install rustfmt run
-It also means that there will be some cases we can't format and we have to give
-up. I think that is OK. Hopefully they are rare enough that manually fixing them
-is not painful. Better to have a tool that gives great code in 99% of cases and
-fails in 1% than a tool which gives 50% great code and 50% ugly code, but never
-fails.
+```
+cargo install --no-default-features rustfmt
+```
+## Running
-### Incremental development
+You can run Rustfmt by just typing `rustfmt filename` if you used `cargo
+install`. This runs rustfmt on the given file, if the file includes out of line
+modules, then we reformat those too. So to run on a whole module or crate, you
+just need to run on the root file (usually mod.rs or lib.rs). Rustfmt can also
+read data from stdin. Alternatively, you can use `cargo fmt` to format all
+binary and library targets of your crate.
-I want rustfmt to be useful as soon as possible and to always be useful. I
-specifically don't want to have to wait for a feature (or worse, the whole tool)
-to be perfect before it is useful. The main ways this is achieved is to output
-the source code where we can't yet reformat, be able to turn off new features
-until they are ready, and the 'do no harm' principle (see next section).
+You'll probably want to specify the write mode. Currently, there are modes for
+diff, replace, overwrite, display, coverage, and checkstyle.
+* `replace` Is the default and overwrites the original files after creating backups of the files.
+* `overwrite` Overwrites the original files _without_ creating backups.
+* `display` Will print the formatted files to stdout.
+* `diff` Will print a diff between the original files and formatted files to stdout.
+* `checkstyle` Will output the lines that need to be corrected as a checkstyle XML file,
+ that can be used by tools like Jenkins.
-### First, do no harm
+The write mode can be set by passing the `--write-mode` flag on
+the command line. For example `rustfmt --write-mode=display src/filename.rs`
-Until rustfmt it perfect, there will always be a trade-off between doing more and
-doing existing things well. I want to err on the side of the latter.
-Specifically, rustfmt should never take OK code and make it look worse. If we
-can't make it better, we should leave it as is. That might mean being less
-aggressive than we like or using configurability.
+`cargo fmt` uses `--write-mode=replace` by default.
+If `rustfmt` successfully reformatted the code it will exit with `0` exit
+status. Exit status `1` signals some unexpected error, like an unknown option or
+a failure to read a file. Exit status `2` is returned if there are syntax errors
+in the input files. `rustfmt` can't format syntatically invalid code. Finally,
+exit status `3` is returned if there are some issues which can't be resolved
+automatically. For example, if you have a very long comment line `rustfmt`
+doesn't split it. Instead it prints a warning and exits with `3`.
-### Use the source code as guidance
+You can run `rustfmt --help` for more information.
-There are often multiple ways to format code and satisfy standards. Where this
-is the case, we should use the source code as a hint for reformatting.
-Furthermore, where the code has been formatted in a particular way that satisfies
-the coding standard, it should not be changed (this is sometimes not possible or
-not worthwhile due to uniformity being desirable, but it is a useful goal).
+## Running Rustfmt from your editor
-### Architecture details
+* [Vim](http://johannh.me/blog/rustfmt-vim.html)
+* [Emacs](https://github.com/fbergroth/emacs-rustfmt)
+* [Sublime Text 3](https://packagecontrol.io/packages/BeautifyRust)
+* [Atom](atom.md)
+* Visual Studio Code using [RustyCode](https://github.com/saviorisdead/RustyCode) or [vsc-rustfmt](https://github.com/Connorcpu/vsc-rustfmt)
-We use the AST from libsyntax. We use libsyntax's visit module to walk the AST
-to find starting points for reformatting. Eventually, we should reformat everything
-and we shouldn't need the visit module. We keep track of the last formatted
-position in the code, and when we reformat the next piece of code we make sure
-to output the span for all the code in between (handled by missed_spans.rs).
+## How to build and test
-Our visitor keeps track of the desired current indent due to blocks (
-`block_indent`). Each `visit_*` method reformats code according to this indent
-and `IDEAL_WIDTH` and `MAX_WIDTH` (which should one day be supplied from a
-config file). Most reformatting done in the `visit_*` methods is a bit hackey
-and is meant to be temporary until it can be done properly.
+`cargo build` to build.
-There are a bunch of methods called `rewrite_*`. There do the bulk of the
-reformatting. These take the AST node to be reformatted (this may not literally
-be an AST node from libsyntax, there might be multiple parameters describing a
-logical node), the current indent, and the current width budget. They return a
-`String` (or sometimes an `Option<String>`) which formats the code in the box
-given by the indent and width budget. If the method fails, it returns `None` and
-the calling method then has to fallback in some way to give the callee more space.
+`cargo test` to run all tests.
-So, in summary to format a node, we calculate the width budget and then walk down
-the tree from the node. At a leaf, we generate an actual string and then unwind,
-combining these strings as we go back up the tree.
+To run rustfmt after this, use `cargo run --bin rustfmt -- filename`. See the
+notes above on running rustfmt.
-For example, consider a method definition:
-```
- fn foo(a: A, b: B) {
- ...
- }
-```
+## Configuring Rustfmt
-We start at indent 4, the rewrite function for the whole function knows it must
-write `fn foo(` before the arguments and `) {` after them, assuming the max width
-is 100, it thus asks the rewrite argument list function to rewrite with an indent
-of 11 and in a width of 86. Assuming that is possible (obviously in this case),
-it returns a string for the arguments and it can make a string for the function
-header. If the arguments couldn't be fitted in that space, we might try to
-fallback to a hanging indent, so we try again with indent 8 and width 89.
+Rustfmt is designed to be very configurable. You can create a TOML file called
+rustfmt.toml, place it in the project directory and it will apply the options
+in that file. See `rustfmt --config-help` for the options which are available,
+or if you prefer to see source code, [src/config.rs](src/config.rs).
+By default, Rustfmt uses a style which (mostly) conforms to the
+[Rust style guidelines](https://github.com/rust-lang/rust/tree/master/src/doc/style).
+There are many details which the style guidelines do not cover, and in these
+cases we try to adhere to a style similar to that used in the
+[Rust repo](https://github.com/rust-lang/rust). Once Rustfmt is more complete, and
+able to re-format large repositories like Rust, we intend to go through the Rust
+RFC process to nail down the default style in detail.
-## Contributing
+If there are styling choices you don't agree with, we are usually happy to add
+options covering different styles. File an issue, or even better, submit a PR.
-### Test and file issues
-It would be really useful to have people use rustfmt on their projects and file
-issues where it does something you don't expect.
+## Gotchas
-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. I hope to get the whole repo consistently rustfmt'ed and to
-replace `make tidy` with rustfmt as a medium-term goal.
+* For things you do not want rustfmt to mangle, use one of
-### Create test cases
+ ```rust
+ #[rustfmt_skip] // requires nightly and #![feature(custom_attribute)] in crate root
+ #[cfg_attr(rustfmt, rustfmt_skip)] // works in stable
+ ```
+* When you run rustfmt, place a file named rustfmt.toml in target file
+ directory or its parents to override the default settings of rustfmt.
+* After successful compilation, a `rustfmt` executable can be found in the
+ target directory.
-Having a strong test suite for a tool like this is essential. It is very easy
-to create regressions. Any tests you can add are very much appreciated.
-### Hack!
+## License
-Here are some [good starting issues](https://github.com/nrc/rustfmt/issues?q=is%3Aopen+is%3Aissue+label%3Aeasy).
-Note than some of those issues tagged 'easy' are not that easy and might be better
-second issues, rather than good first issues to fix.
+Rustfmt is distributed under the terms of both the MIT license and the
+Apache License (Version 2.0).
-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.
+See [LICENSE-APACHE](LICENSE-APACHE) and [LICENSE-MIT](LICENSE-MIT) for details.
projects / rust.git / blobdiff