This crate provides a procedural macro for indented string literals. The indoc!() macro takes a multiline string literal and un-indents it at compile time so the leftmost non-space character is in the first column.

[dependencies]
indoc = "2"

Compiler requirement: rustc 1.56 or greater.

use indoc::indoc;

fn main() {
    let testing = indoc! {"
        def hello():
            print('Hello, world!')

        hello()
    "};
    let expected = "def hello():\n    print('Hello, world!')\n\nhello()\n";
    assert_eq!(testing, expected);
}

Indoc also works with raw string literals:

use indoc::indoc;

fn main() {
    let testing = indoc! {r#"
        def hello():
            print("Hello, world!")

        hello()
    "#};
    let expected = "def hello():\n    print(\"Hello, world!\")\n\nhello()\n";
    assert_eq!(testing, expected);
}

And byte string literals:

use indoc::indoc;

fn main() {
    let testing = indoc! {b"
        def hello():
            print('Hello, world!')

        hello()
    "};
    let expected = b"def hello():\n    print('Hello, world!')\n\nhello()\n";
    assert_eq!(testing[..], expected[..]);
}

The indoc crate exports five additional macros to substitute conveniently for the standard library's formatting macros:

• formatdoc!($fmt, ...) — equivalent to format!(indoc!($fmt), ...)
• printdoc!($fmt, ...) — equivalent to print!(indoc!($fmt), ...)
• eprintdoc!($fmt, ...) — equivalent to eprint!(indoc!($fmt), ...)
• writedoc!($dest, $fmt, ...) — equivalent to write!($dest, indoc!($fmt), ...)
• concatdoc!(...) — equivalent to concat!(...) with each string literal wrapped in indoc!

use indoc::{concatdoc, printdoc};

const HELP: &str = concatdoc! {"
    Usage: ", env!("CARGO_BIN_NAME"), " [options]

    Options:
        -h, --help
"};

fn main() {
    printdoc! {"
        GET {url}
        Accept: {mime}
        ",
        url = "http://localhost:8080",
        mime = "application/json",
    }
}

The following rules characterize the behavior of the indoc!() macro:

1. Count the leading spaces of each line, ignoring the first line and any lines that are empty or contain spaces only.
2. Take the minimum.
3. If the first line is empty i.e. the string begins with a newline, remove the first line.
4. Remove the computed number of spaces from the beginning of each line.

Indoc's indentation logic is available in the unindent crate. This may be useful for processing strings that are not statically known at compile time.

The crate exposes two functions:

• unindent(&str) -> String
• unindent_bytes(&[u8]) -> Vec<u8>

use unindent::unindent;

fn main() {
    let indented = "
            line one
            line two";
    assert_eq!("line one\nline two", unindent(indented));
}