As originally discussed and described in https://github.com/rust-lang/style-team/issues/196#issuecomment-2810856708, we want to do the following: - We want to always break a match arm body onto a new line if the pattern spans multiple lines (and thus always use braces for such a match arm, given the default setting of `match_arm_blocks`). - We want to say that whenever we wrap the `{` to a new line, we always put the `=>` on the same line as the `{` rather than hanging it on the end of the previous line. In other words, "never break between the `=>` and the `{`". - We want to break the `=> {` onto a new line if the pattern spans multiple lines and has indented continuation lines (because it has an `if` guard). cc @rust-lang/style