Change:
(backward-word 1)) (current-column)))) <ins> (defun rust-rewind-to-beginning-of-current-level-expr () (let ((current-level (rust-paren-level))) (back-to-indentation) (while (> (rust-paren-level) current-level) (backward-up-list) (back-to-indentation)))) </ins> (defun rust-mode-indent-line () (interactive) (let ((indent (save-excursion (back-to-indentation) <del> (let ((level (rust-paren-level))) </del> <ins> ;; Point is now at beginning of current line (let* ((level (rust-paren-level)) (baseline ;; Our "baseline" is one level out from the indentation of the expression ;; containing the innermost enclosing opening bracket.  That ;; way if we are within a block that has a different ;; indentation than this mode would give it, we still indent ;; the inside of it correctly relative to the outside. (if (= 0 level) 0 (save-excursion (backward-up-list) (rust-rewind-to-beginning-of-current-level-expr) (+ (current-column) rust-indent-offset))))) </ins> (cond ;; A function return type is indented to the corresponding function arguments ((looking-at "->") (save-excursion (backward-list) (or (rust-align-to-expr-after-brace) <del> (* rust-indent-offset (+ 1 level))))) </del> <ins> (+ baseline rust-indent-offset)))) </ins> ;; A closing brace is 1 level unindended <del> ((looking-at "}") (* rust-indent-offset (- level 1))) </del> <ins> ((looking-at "}") (- baseline rust-indent-offset)) </ins> ;; Doc comments in /** style with leading * indent to line up the *s ((and (nth 4 (syntax-ppss)) (looking-at "*")) <del> (+ 1 (* rust-indent-offset level))) </del> <ins> (+ 1 baseline)) </ins> ;; If we're in any other token-tree / sexp, then: <del> ;;  - [ or ( means line up with the opening token ;;  - { means indent to either nesting-level * rust-indent-offset, ;;    or one further indent from that if either current line ;;    begins with 'else', or previous line didn't end in ;;    semi, comma or brace (other than whitespace and line ;;    comments) , and wasn't an attribute.  But if we have ;;    something after the open brace and ending with a comma, ;;    treat it as fields and align them.  PHEW. ((> level 0) (let ((pt (point))) (rust-rewind-irrelevant) (backward-up-list) (or (and (looking-at "[[({]") (rust-align-to-expr-after-brace)) (progn (goto-char pt) (back-to-indentation) (if (looking-at "<else>") (* rust-indent-offset (+ 1 level)) (progn (goto-char pt) (beginning-of-line) (rust-rewind-irrelevant) (end-of-line) (if (looking-back "[[,;{}(][[:space:]]*(?://.*)?") (* rust-indent-offset level) (back-to-indentation) (if (looking-at "#") (* rust-indent-offset level) (* rust-indent-offset (+ 1 level)))))))))) ;; Otherwise we're in a column-zero definition (t 0)))))) (cond ;; If we're to the left of the indentation, reindent and jump to it. ((<= (current-column) indent) (indent-line-to indent)) ;; We're to the right; if it needs indent, do so but save excursion. ((not (eq (current-indentation) indent)) (save-excursion (indent-line-to indent)))))) </del> <ins> (t (or ;; If we are inside a pair of braces, with something after the ;; open brace on the same line and ending with a comma, treat ;; it as fields and align them. (when (> level 0) (save-excursion (rust-rewind-irrelevant) (backward-up-list) ;; Point is now at the beginning of the containing set of braces (rust-align-to-expr-after-brace))) (progn (back-to-indentation) ;; Point is now at the beginning of the current line (if (or ;; If this line begins with "else" or "{", stay on the ;; baseline as well (we are continuing an expression, ;; but the "else" or "{" should align with the beginning ;; of the expression it's in.) (looking-at "<else>|{") (save-excursion (rust-rewind-irrelevant) ;; Point is now at the end of the previous ine (or ;; If we are at the first line, no indentation is needed, so stay at baseline... (= 1 (line-number-at-pos (point))) ;; ..or if the previous line ends with any of these: ;;     { ? : ( , ; [ } ;; then we are at the beginning of an expression, so stay on the baseline... (looking-back "[(,:;?[{}]|[^|]|") ;; or if the previous line is the end of an attribute, stay at the baseline... (progn (rust-rewind-to-beginning-of-current-level-expr) (looking-at "#"))))) baseline ;; Otherwise, we are continuing the same expression from the previous line, ;; so add one additional indent level (+ baseline rust-indent-offset)))))))))) (when (not (eq (current-indentation) indent)) ;; If we're at the beginning of the line (before or at the current ;; indentation), jump with the indentation change.  Otherwise, save the ;; excursion so that adding the indentations will leave us at the ;; equivalent position within the line to where we were before. (if (<= (current-column) (current-indentation)) (indent-line-to indent) (save-excursion (indent-line-to indent)))))) </ins> ;; Font-locking definitions and helpers

Discussion:
There are several common cases where the emacs mode gets the indentation incorrect. I'll list the examples as I believe they should be formatted. indent after open paren with no argument: with arguments: field names:
Oh, and the motivating example for filing the bug: comments don't work quite right. and also you should be able to hit M-q and have it reflow correctly.
I've found trailing line comments breaks the indentation of the next line: (Not sure if this is worth a separate bug.)
Another example is a pattern relative to an indented match: Also, I believe patterns in general are indented incorrectly, though admittedly I'm not sure what the standard is. My preference is to keep all patterns at the same level of indentation, as shown here:
If we're going to fix , we should try to also take the time to fix the other doc comment variations, namely , if possible.
part of