Line breaks in string literal + ascii escape code changes meaning

Input

const ASCII_ESCAPE: &str = "id\u{1f}1\u{1f}/Users/nixon/dev/rs/gitstatusd\u{1f}1c9be4fe5460a30e70de9cbf99c3ec7064296b28\u{1f}master\u{1f}\u{1f}\u{1f}\u{1f}\u{1f}7\u{1f}0\u{1f}1\u{1f}0\u{1f}1\u{1f}0\u{1f}0\u{1f}0\u{1f}\u{1f}0\u{1f}0\u{1f}0\u{1f}\u{1f}\u{1f}0\u{1f}0\u{1f}0\u{1f}0";

Output

const ASCII_ESCAPE: &str = "id\u{1f}1\u{1f}/Users/nixon/dev/rs/gitstatusd\\
                            u{1f}1c9be4fe5460a30e70de9cbf99c3ec7064296b28\u{1f}master\u{1f}\u{1f}\\
                            u{1f}\u{1f}\u{1f}7\u{1f}0\u{1f}1\u{1f}0\u{1f}1\u{1f}0\u{1f}0\u{1f}0\\
                            u{1f}\u{1f}0\u{1f}0\u{1f}0\u{1f}\u{1f}\u{1f}0\u{1f}0\u{1f}0\u{1f}0";

Expected output

const ASCII_ESCAPE: &str = "id\u{1f}1\u{1f}/Users/nixon/dev/rs/gitstatusd\
                            \u{1f}1c9be4fe5460a30e70de9cbf99c3ec7064296b28\u{1f}master\u{1f}\u{1f}\
                            \u{1f}\u{1f}\u{1f}7\u{1f}0\u{1f}1\u{1f}0\u{1f}1\u{1f}0\u{1f}0\u{1f}0\
                            \u{1f}\u{1f}0\u{1f}0\u{1f}0\u{1f}\u{1f}\u{1f}0\u{1f}0\u{1f}0\u{1f}0";

The two outputs are different. Playground. As the split is across the "\u{1f}" it breaks this up and instead creates a \\", which means the line gets a "\" and indentation as the "\" that was inserted was escaped by the "\" that was ment to escape the hex literal.

rustfmt.toml

format_strings = true

Meta

• rustfmt version: rustfmt 1.4.22-nightly (97d03010 2020-10-04)
• From where did you install rustfmt?: rustup

Reproduce the formatting change from the issue using rustfmt.toml with format_strings = true and the provided Playground example. Trace string-literal line breaking around the \u{1f} escape, then verify that formatted output preserves the escape sequence and produces the expected multiline string.