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-tools is
-probably the best channel. Feel free to also ask questions on issues, or file
-new issues specifically to get help.
+contributing or need help with anything, please ping nrc on irc, #rust-dev-tools
+on irc.mozilla.org is probably the best channel. 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
+Conduct](CODE_OF_CONDUCT.md).
## Test and file issues
identified.
Without explicit settings, the tests will be run using rustfmt's default
-configuration. It is possible to run a test using non-default settings by
-including configuration parameters in comments at the top of the file. For
-example: to use 3 spaces per tab, start your test with
+configuration. It is possible to run a test using non-default settings in several
+ways. Firstly, you can include configuration parameters in comments at the top
+of the file. For example: to use 3 spaces per tab, start your test with
`// rustfmt-tab_spaces: 3`. Just remember that the comment is part of the input,
so include in both the source and target files! It is also possible to
explicitly specify the name of the expected output file in the target directory.
-Use `// rustfmt-target: filename.rs` for this. Finally, you can use a custom
+Use `// rustfmt-target: filename.rs` for this. You can also specify a custom
configuration by using the `rustfmt-config` directive. Rustfmt will then use
that toml file located in `./tests/config/` for its configuration. Including
`// rustfmt-config: small_tabs.toml` will run your test with the configuration
-file found at `./tests/config/small_tabs.toml`.
+file found at `./tests/config/small_tabs.toml`. The final option is used when the
+test source file contains no configuration parameter comments. In this case, the
+test harness looks for a configuration file with the same filename as the test
+file in the `./tests/config/` directory, so a test source file named `test-indent.rs`
+would need a configuration file named `test-indent.toml` in that directory. As an
+example, the `issue-1111.rs` test file is configured by the file
+`./tests/config/issue-1111.toml`.
## Hack!
-Here are some [good starting issues](https://github.com/nrc/rustfmt/issues?q=is%3Aopen+is%3Aissue+label%3Aeasy).
+Here are some [good starting issues](https://github.com/rust-lang-nursery/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.
### A quick tour of Rustfmt
-Rustfmt is basically a pretty printer - that is, it's mode of operation is to
+Rustfmt is basically a pretty printer - that is, its mode of operation is to
take an AST (abstract syntax tree) and print it in a nice way (including staying
under the maximum permitted width for a line). In order to get that AST, we
first have to parse the source text, we use the Rust compiler's parser to do
-that (see [src/lib.rs]). We shy away from doing anything too fancy, such as
+that (see [src/lib.rs](src/lib.rs)). We shy away from doing anything too fancy, such as
algebraic approaches to pretty printing, instead relying on an heuristic
approach, 'manually' crafting a string for each AST node. This results in quite
a lot of code, but it is relatively simple.
There are different nodes for every kind of item and expression in Rust. For
more details see the source code in the compiler -
[ast.rs](https://dxr.mozilla.org/rust/source/src/libsyntax/ast.rs) - and/or the
-[docs](http://manishearth.github.io/rust-internals-docs/syntax/ast/index.html).
+[docs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast/index.html).
Many nodes in the AST (but not all, annoyingly) have a `Span`. A `Span` is a
range in the source code, it can easily be converted to a snippet of source
'top level' items. Then we can reproduce that text pretty much verbatim. We only
count spans we actually reformat, so if we can't format a span it is not missed
completely, but is reproduced in the output without being formatted. This is
-mostly handled in [src/missed_spans.rs]. See also `FmtVisitor::last_pos` in
-[src/visitor.rs].
+mostly handled in [src/missed_spans.rs](src/missed_spans.rs). See also `FmtVisitor::last_pos` in
+[src/visitor.rs](src/visitor.rs).
#### Some important elements
At the highest level, Rustfmt uses a `Visitor` implementation called `FmtVisitor`
-to walk the AST. This is in [src/visitor.rs]. This is really just used to walk
+to walk the AST. This is in [src/visitor.rs](src/visitor.rs). This is really just used to walk
items, rather than the bodies of functions. We also cover macros and attributes
here. Most methods of the visitor call out to `Rewrite` implementations that
then walk their own children.
-The `Rewrite` trait is defined in [src/rewrite.rs]. It is implemented for many
+The `Rewrite` trait is defined in [src/rewrite.rs](src/rewrite.rs). It is implemented for many
things that can be rewritten, mostly AST nodes. It has a single function,
`rewrite`, which is called to rewrite `self` into an `Option<String>`. The
arguments are `width` which is the horizontal space we write into, and `offset`
into the required width. How to handle this is up to the caller. Often the
caller just gives up, ultimately relying on the missed spans system to paste in
the un-formatted source. A better solution (although not performed in many
-places) is for the caller to shuffle around some of it's other items to make
+places) is for the caller to shuffle around some of its other items to make
more width, then call the function again with more space.
Since it is common for callers to bail out when a callee fails, we often use a
-`try_opt!` macro to make this pattern more succinct.
+`?` operator to make this pattern more succinct.
One way we might find out that we don't have enough space is when computing how much
space we have. Something like `available_space = budget - overhead`. Since
widths are unsized integers, this would cause underflow. Therefore we use
-checked subtraction: `available_space = try_opt!(budget.checked_sub(overhead))`.
-`checked_sub` returns an `Option`, and if we would underflow `try_opt!` returns
+checked subtraction: `available_space = budget.checked_sub(overhead)?`.
+`checked_sub` returns an `Option`, and if we would underflow `?` returns
`None`, otherwise we proceed with the computed space.
Much syntax in Rust is lists: lists of arguments, lists of fields, lists of
array elements, etc. We have some generic code to handle lists, including how to
space them in horizontal and vertical space, indentation, comments between
items, trailing separators, etc. However, since there are so many options, the
-code is a bit complex. Look in [src/lists.rs]. `write_list` is the key function,
+code is a bit complex. Look in [src/lists.rs](src/lists.rs). `write_list` is the key function,
and `ListFormatting` the key structure for configuration. You'll need to make a
`ListItems` for input, this is usually done using `itemize_list`.
Rustfmt strives to be highly configurable. Often the first part of a patch is
creating a configuration option for the feature you are implementing. All
-handling of configuration options is done in [src/config.rs]. Look for the
+handling of configuration options is done in [src/config/mod.rs](src/config/mod.rs). Look for the
`create_config!` macro at the end of the file for all the options. The rest of
the file defines a bunch of enums used for options, and the machinery to produce
the config struct and parse a config file, etc. Checking an option is done by
-accessing the correct field on the config struct, e.g., `config.max_width`. Most
+accessing the correct field on the config struct, e.g., `config.max_width()`. Most
functions have a `Config`, or one can be accessed via a visitor or context of
some kind.
projects / rust.git / blobdiff