emacs/runtime/indent/rust.vim

" Vim indent file
" Language:         Rust
" Author:           Chris Morgan <me@chrismorgan.info>
" Last Change:      2017 Jun 13
" For bugs, patches and license go to https://github.com/rust-lang/rust.vim

" Only load this indent file when no other was loaded.
if exists("b:did_indent")
	finish
endif
let b:did_indent = 1

setlocal cindent
setlocal cinoptions=L0,(0,Ws,J1,j1
setlocal cinkeys=0{,0},!^F,o,O,0[,0]
" Don't think cinwords will actually do anything at all... never mind
setlocal cinwords=for,if,else,while,loop,impl,mod,unsafe,trait,struct,enum,fn,extern

" Some preliminary settings
setlocal nolisp		" Make sure lisp indenting doesn't supersede us
setlocal autoindent	" indentexpr isn't much help otherwise
" Also do indentkeys, otherwise # gets shoved to column 0 :-/
setlocal indentkeys=0{,0},!^F,o,O,0[,0]

setlocal indentexpr=GetRustIndent(v:lnum)

" Only define the function once.
if exists("*GetRustIndent")
	finish
endif

let s:save_cpo = &cpo
set cpo&vim

" Come here when loading the script the first time.

function! s:get_line_trimmed(lnum)
	" Get the line and remove a trailing comment.
	" Use syntax highlighting attributes when possible.
	" NOTE: this is not accurate; /* */ or a line continuation could trick it
	let line = getline(a:lnum)
	let line_len = strlen(line)
	if has('syntax_items')
		" If the last character in the line is a comment, do a binary search for
		" the start of the comment.  synID() is slow, a linear search would take
		" too long on a long line.
		if synIDattr(synID(a:lnum, line_len, 1), "name") =~ 'Comment\|Todo'
			let min = 1
			let max = line_len
			while min < max
				let col = (min + max) / 2
				if synIDattr(synID(a:lnum, col, 1), "name") =~ 'Comment\|Todo'
					let max = col
				else
					let min = col + 1
				endif
			endwhile
			let line = strpart(line, 0, min - 1)
		endif
		return substitute(line, "\s*$", "", "")
	else
		" Sorry, this is not complete, nor fully correct (e.g. string "//").
		" Such is life.
		return substitute(line, "\s*//.*$", "", "")
	endif
endfunction

function! s:is_string_comment(lnum, col)
	if has('syntax_items')
		for id in synstack(a:lnum, a:col)
			let synname = synIDattr(id, "name")
			if synname == "rustString" || synname =~ "^rustComment"
				return 1
			endif
		endfor
	else
		" without syntax, let's not even try
		return 0
	endif
endfunction

function GetRustIndent(lnum)

	" Starting assumption: cindent (called at the end) will do it right
	" normally. We just want to fix up a few cases.

	let line = getline(a:lnum)

	if has('syntax_items')
		let synname = synIDattr(synID(a:lnum, 1, 1), "name")
		if synname == "rustString"
			" If the start of the line is in a string, don't change the indent
			return -1
		elseif synname =~ '\(Comment\|Todo\)'
					\ && line !~ '^\s*/\*'  " not /* opening line
			if synname =~ "CommentML" " multi-line
				if line !~ '^\s*\*' && getline(a:lnum - 1) =~ '^\s*/\*'
					" This is (hopefully) the line after a /*, and it has no
					" leader, so the correct indentation is that of the
					" previous line.
					return GetRustIndent(a:lnum - 1)
				endif
			endif
			" If it's in a comment, let cindent take care of it now. This is
			" for cases like "/*" where the next line should start " * ", not
			" "* " as the code below would otherwise cause for module scope
			" Fun fact: "  /*\n*\n*/" takes two calls to get right!
			return cindent(a:lnum)
		endif
	endif

	" cindent gets second and subsequent match patterns/struct members wrong,
	" as it treats the comma as indicating an unfinished statement::
	"
	" match a {
	"     b => c,
	"         d => e,
	"         f => g,
	" };

	" Search backwards for the previous non-empty line.
	let prevlinenum = prevnonblank(a:lnum - 1)
	let prevline = s:get_line_trimmed(prevlinenum)
	while prevlinenum > 1 && prevline !~ '[^[:blank:]]'
		let prevlinenum = prevnonblank(prevlinenum - 1)
		let prevline = s:get_line_trimmed(prevlinenum)
	endwhile

	" Handle where clauses nicely: subsequent values should line up nicely.
	if prevline[len(prevline) - 1] == ","
				\ && prevline =~# '^\s*where\s'
		return indent(prevlinenum) + 6
	endif

	if prevline[len(prevline) - 1] == ","
				\ && s:get_line_trimmed(a:lnum) !~ '^\s*[\[\]{}]'
				\ && prevline !~ '^\s*fn\s'
				\ && prevline !~ '([^()]\+,$'
				\ && s:get_line_trimmed(a:lnum) !~ '^\s*\S\+\s*=>'
		" Oh ho! The previous line ended in a comma! I bet cindent will try to
		" take this too far... For now, let's normally use the previous line's
		" indent.

		" One case where this doesn't work out is where *this* line contains
		" square or curly brackets; then we normally *do* want to be indenting
		" further.
		"
		" Another case where we don't want to is one like a function
		" definition with arguments spread over multiple lines:
		"
		" fn foo(baz: Baz,
		"        baz: Baz) // <-- cindent gets this right by itself
		"
		" Another case is similar to the previous, except calling a function
		" instead of defining it, or any conditional expression that leaves
		" an open paren:
		"
		" foo(baz,
		"     baz);
		"
		" if baz && (foo ||
		"            bar) {
		"
		" Another case is when the current line is a new match arm.
		"
		" There are probably other cases where we don't want to do this as
		" well. Add them as needed.
		return indent(prevlinenum)
	endif

	if !has("patch-7.4.355")
		" cindent before 7.4.355 doesn't do the module scope well at all; e.g.::
		"
		" static FOO : &'static [bool] = [
		" true,
		"	 false,
		"	 false,
		"	 true,
		"	 ];
		"
		"	 uh oh, next statement is indented further!

		" Note that this does *not* apply the line continuation pattern properly;
		" that's too hard to do correctly for my liking at present, so I'll just
		" start with these two main cases (square brackets and not returning to
		" column zero)

		call cursor(a:lnum, 1)
		if searchpair('{\|(', '', '}\|)', 'nbW',
					\ 's:is_string_comment(line("."), col("."))') == 0
			if searchpair('\[', '', '\]', 'nbW',
						\ 's:is_string_comment(line("."), col("."))') == 0
				" Global scope, should be zero
				return 0
			else
				" At the module scope, inside square brackets only
				"if getline(a:lnum)[0] == ']' || search('\[', '', '\]', 'nW') == a:lnum
				if line =~ "^\\s*]"
					" It's the closing line, dedent it
					return 0
				else
					return shiftwidth()
				endif
			endif
		endif
	endif

	" Fall back on cindent, which does it mostly right
	return cindent(a:lnum)
endfunction

let &cpo = s:save_cpo
unlet s:save_cpo