rsfmt ---- Rust Source Code Formatter

https://github.com/zBaitu/rsfmt

Active again from old repo: rfmt

Overview

rsfmt is a Rust source code formatter. Yes, there is already an official tool rustfmt. So why write another one?

• rustfmt is great for configurable, but there are still some style that I don't like in my personal taste.

• Write a code formatter for Rust can make me learn Rust more deeply, for example, the AST of Rust.

• For fun :)

Version

Support for Rust 1.60 nightly

Install, Build

• Install

cargo install rsfmt

• Build

git clone git@github.com:zBaitu/rsfmt.git
cargo build --release

Usage

rsfmt 1.60.0

USAGE:
    rsfmt [FLAGS] [input]

FLAGS:
    -a, --ast          Prints the rust original syntax ast debug info
    -c, --check        Only check without output or overwrite
    -d, --debug        Prints the rsfmt ir debug info
    -h, --help         Prints help information
    -k, --keep         Keep going when error occurred
    -o, --overwrite    Overwrite the source file
    -p, --print        Prints the rsfmt ir simple format
    -V, --version      Prints version information

ARGS:
    <input>    Input file or dir. If `input` is a dir, rsfmt will do action for all files in this dir recursively.
               If neither `options` nor `input` is specified, rsfmt will format source code from stdin

Running rsfmt from your editor

In fact, I only use rsfmt with IntelliJ now. Just add an external tool as below.

Other editor usage can access to Running Rustfmt from your editor. I think maybe just replace the rustfmt to rsfmt.

Features

Comparing to rustfmt, there are some main different features from rsfmt:

• Keep wrap from user input.
• Different align strategy.
• Group crate, use, mod, attributes and sort them.
• DO NOT format doc, comment, string. You can use the check function to show exceed lines and trailing white space lines.
• Provide check, directory recursively, ast dump, debug.
• Nightly features.

The following part will show such features in detail, with some existing issues from rustfmt.

Keep wrap from user input

For the issue: rustfmt reformats bit manipiulations.

fn main() {
    let (a, b, c, d) = (0, 0, 0, 0);
    let _ = u32::from_be(((a as u32) << 24) |
                         ((b as u32) << 16) |
                         ((c as u32) <<  8) |
                          (d as u32) <<  0);
}

• rustfmt

fn main() {
    let (a, b, c, d) = (0, 0, 0, 0);
    let _ =
        u32::from_be(((a as u32) << 24) | ((b as u32) << 16) | ((c as u32) << 8) | (d as u32) << 0);
}

Of course, you can use #[rustfmt_skip] to avoid such code, but in my personal opinon, I really don't like to add other code just for the source formatting tool.

• rsfmt

fn main() {
    let (a, b, c, d) = (0, 0, 0, 0);
    let _ = u32::from_be(((a as u32) << 24) | 
                         ((b as u32) << 16) | 
                         ((c as u32) << 8) | 
                         (d as u32) << 0);
}

It looks OK, isn't it? Why rsfmt can keep the user wrap? Because of the rsfmt ir. The custom ir of Rust AST record location information of every element as far as possible. Look another example:

fn main() {
    let ref_packet = [0xde, 0xf0, 0x12, 0x34, 0x45, 0x67,
                     0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc,
                     0x86, 0xdd];
}

• rustfmt

fn main() {
    let ref_packet = [
        0xde, 0xf0, 0x12, 0x34, 0x45, 0x67, 0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0x86, 0xdd,
    ];
}

• rsfmt

fn main() {
    let ref_packet = [0xde, 0xf0, 0x12, 0x34, 0x45, 0x67,
                      0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc,
                      0x86, 0xdd];
}

Different align strategy

I prefer to put parameters on one line as much as possible.

fn main() {
    f(123456789, "abcdefg", "hijklmn", 0987654321, "opqrst", "uvwxyz", 123456789, "abcdefg", "hijklmn", 0987654321, "opqrst", "uvwxyz");
}

• rustfmt

fn main() {
    f(
        123456789, "abcdefg", "hijklmn", 0987654321, "opqrst", "uvwxyz", 123456789, "abcdefg",
        "hijklmn", 0987654321, "opqrst", "uvwxyz",
    );
}

• rsfmt

fn main() {
    f(123456789, "abcdefg", "hijklmn", 0987654321, "opqrst", "uvwxyz", 123456789, "abcdefg", "hijklmn", 0987654321,
      "opqrst", "uvwxyz");
}

If the left align position is beyond limit(It is 40 for now), rsfmt prefer double indent align to function call align. rsfmt make source code left lean, while rustfmt is right lean, I think. An exsiting issue: rustfmt should avoid rightwards drifting big blocks of code

fn main() {
    let mut arms = variants.iter().enumerate().map(|(i, &(ident, v_span, ref summary))| {
        let i_expr = cx.expr_usize(v_span, i);
        let pat = cx.pat_lit(v_span, i_expr);

        let path = cx.path(v_span, vec![substr.type_ident, ident]);
        let thing = rand_thing(cx, v_span, path, summary, |cx, sp| rand_call(cx, sp));
        cx.arm(v_span, vec![ pat ], thing)
    }).collect::<Vec<ast::Arm> >();
}

• rustfmt

fn main() {
    let mut arms = variants
        .iter()
        .enumerate()
        .map(|(i, &(ident, v_span, ref summary))| {
            let i_expr = cx.expr_usize(v_span, i);
            let pat = cx.pat_lit(v_span, i_expr);

            let path = cx.path(v_span, vec![substr.type_ident, ident]);
            let thing = rand_thing(cx, v_span, path, summary, |cx, sp| rand_call(cx, sp));
            cx.arm(v_span, vec![pat], thing)
        })
        .collect::<Vec<ast::Arm>>();
}

• rsfmt

fn main() {
    let mut arms = variants.iter().enumerate().map(|(i, &(ident, v_span, ref summary))| {
        let i_expr = cx.expr_usize(v_span, i);
        let pat = cx.pat_lit(v_span, i_expr);
        let path = cx.path(v_span, vec![substr.type_ident, ident]);
        let thing = rand_thing(cx, v_span, path, summary, |cx, sp| rand_call(cx, sp));
        cx.arm(v_span, vec![pat], thing)
    }).collect::<Vec<ast::Arm>>();
}

The result from rsfmt is not changed, because this source code fits rsfmt's code style.

Group crate, use, mod, attributes and sort them

#![feature(custom_derive)]
#![deny(warnings)]
#![feature(question_mark)]
#![feature(iter_arith)]
#![feature(rustc_private)]

extern crate rst;
extern crate getopts;
extern crate walkdir;

use std::env;
use getopts::Options;

#[macro_use]
mod ts;

mod ir;
mod ft;
mod tr;
mod rsfmt;

• rsfmt

#![deny(warnings)]
#![feature(custom_derive)]
#![feature(iter_arith)]
#![feature(question_mark)]
#![feature(rustc_private)]

extern crate getopts;
extern crate rst;
extern crate walkdir;

use getopts::Options;
use std::env;

#[macro_use]
mod ts;

mod ft;
mod ir;
mod rsfmt;
mod tr;

rsfmt only group items that appear continuously. If on item is special that it must keep its order, like the mod ts;, make it separate from others.

DO NOT format doc, comment, string

There are many issues about doc, comment, string, raw string from rustfmt. I think such element can leave free for user to write anything, any format they want.

Provide check, directory recursively, ast dump

If you want to check is there some line break the code style limit, rsfmt provide check function.

// aaaaa  
// bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
fn main() {
    let a = r#"aaaaaaaaaaaaaaaaaaaaaaaaaaaa  
            bbbbbbbbbbbbbbbbb"#;
}

rsfmt -c g.rs

"g.rs"
trailing_ws_lines: {1, 4}

You can check or overwrite all files in a directory.

rsfmt -c rust/src/libcore
rsfmt -o rust/src/libstd

Maybe you are interested to see the Rust AST of a source code.

// AST
fn main() {}

rsfmt -a a.rs

Crate {
    attrs: [],
    items: [
        Item {
            attrs: [],
            id: NodeId(4294967040),
            span: Span {
                lo: BytePos(
                    7,
                ),
                hi: BytePos(
                    19,
                ),
                ctxt: #0,
            },
            vis: Visibility {
                kind: Inherited,
                span: Span {
                    lo: BytePos(
                        7,
                    ),
                    hi: BytePos(
                        7,
                    ),
                    ctxt: #0,
                },
                tokens: None,
            },
            ident: main#0,
            kind: Fn(
                FnKind(
                    Final,
                    FnSig {
                        header: FnHeader {
                            unsafety: No,
                            asyncness: No,
                            constness: No,
                            ext: None,
                        },
                        decl: FnDecl {
                            inputs: [],
                            output: Default(
                                Span {
                                    lo: BytePos(
                                        17,
                                    ),
                                    hi: BytePos(
                                        17,
                                    ),
                                    ctxt: #0,
                                },
                            ),
                        },
                        span: Span {
                            lo: BytePos(
                                7,
                            ),
                            hi: BytePos(
                                16,
                            ),
                            ctxt: #0,
                        },
                    },
                    Generics {
                        params: [],
                        where_clause: WhereClause {
                            has_where_token: false,
                            predicates: [],
                            span: Span {
                                lo: BytePos(
                                    16,
                                ),
                                hi: BytePos(
                                    16,
                                ),
                                ctxt: #0,
                            },
                        },
                        span: Span {
                            lo: BytePos(
                                14,
                            ),
                            hi: BytePos(
                                14,
                            ),
                            ctxt: #0,
                        },
                    },
                    Some(
                        Block {
                            stmts: [],
                            id: NodeId(4294967040),
                            rules: Default,
                            span: Span {
                                lo: BytePos(
                                    17,
                                ),
                                hi: BytePos(
                                    19,
                                ),
                                ctxt: #0,
                            },
                            tokens: None,
                        },
                    ),
                ),
            ),
            tokens: None,
        },
    ],
    span: Span {
        lo: BytePos(
            7,
        ),
        hi: BytePos(
            19,
        ),
        ctxt: #0,
    },
    proc_macros: [],
}

------------------------------------------------------------------------------------------------------------------------

0: Isolated [
    "// AST",
]

Drawbacks

As rsfmt is written as a personal tool(toy) for my daily develop, it lacks some common features now.

• No config
  rustfmt provide lots of config option, but rsfmt provide none. Code style is something like food, everyone has his taste. Although rustfmt has many configs now, there are still new config require open in issues. If majority part of rsfmt's style suit your taste, you can clone and make some small modification, such as LF, max width, indent.
• Only support for some kinds of comments
  Comment can appear anywhere in source code, is it difficult to support all kinds of comment, as comment info does not exist on AST node. On the other hand, I don't think some tricky comment is really need. The following source with comment, which comment disappeared means that it is not supported by rsfmt.

// aaaaa

// bbbbb
struct A { // ccccc-DISAPPEARED
    // ddddd
    a: bool, // eeeee
    b: i32, // ffff
    // ggggg
} // hhhhh

// iiiii
fn f(a: bool, /* jjjjj-DISAPPEARED */ b: i32, /* kkkkk-DISAPPEARED */) -> bool { // lllll-DISAPPEARED
    // mmmmm
    const b: bool = false;                  // nnnnn
    let mut a = true;       // ooooo
    a = false; // ppppp
    a!();// qqqqq
    a // rrrrr
} // sssss
// ttttt

// uuuuu

• rsfmt

// aaaaa

// bbbbb
struct A {
    // ddddd
    a: bool, // eeeee
    b: i32, // ffff
    // ggggg
} // hhhhh

// iiiii
fn f(a: bool, b: i32) -> bool {
    // mmmmm
    const b: bool = false; // nnnnn
    let mut a = true; // ooooo
    a = false; // ppppp
    a!(); // qqqqq
    a // rrrrr
} // sssss
// ttttt

// uuuuu