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+" Numeric comparison function to sort in a Vim v7.0 compatible way
+function! s:CompareNumeric(a, b) abort
+ return a:a > a:b ? 1 : -1
+endfunction
+
+" Entry point for plugin
+function! detect_indent#() abort
+
+ " For spaces, we count both the total space-indented lines, and also the
+ " count of lines indexed by space count, so that if we need to, we can
+ " figure out a good 'shiftwidth' setting; for tabs, we just count the
+ " indented lines, since we won't need to set 'shiftwidth' for that.
+ "
+ let tabs = 0
+ let spaces = {
+ \ 'hist': {},
+ \ 'total': 0,
+ \}
+
+ " Figure out how many lines we'll check; cap this to 1,024, or whatever the
+ " user configured
+ let total = max([line('$'), get(g:, 'detect_indent_limit', 1024)])
+
+ " Iterate through the lines
+ for line in getline(1, total)
+
+ " If there are leading tabs, we'll call this a tab-indented line; bump the
+ " appropriate count, and skip the rest of the loop.
+ "
+ if matchstr(line, '^\t*') !=# ''
+ let tabs += 1
+ continue
+ endif
+
+ " Figure out count of space indenting; skip to the next line if it's zero
+ let indent = strlen(matchstr(line, '^ *'))
+ if indent == 0
+ continue
+ endif
+
+ " Increment the count of space-indented lines
+ let spaces['total'] += 1
+
+ " Create a dictionary entry in the histogram for this indent if necessary,
+ " and increment that counter
+ "
+ if !has_key(spaces['hist'], indent)
+ let spaces['hist'][indent] = 0
+ endif
+ let spaces['hist'][indent] += 1
+
+ endfor
+
+ " If the value for 'expandtab' as determined by the user's configuration
+ " matches the expected dominance of space-indented lines over tab-indented
+ " lines, we're already using the right setting, and we stop here
+ "
+ if &expandtab == (spaces['total'] >= tabs)
+ return
+ endif
+
+ " If 'expandtab' is set, we need to unset it and switch to pure tab
+ " indenting; that's straightforward, we just need to make sure 'shiftwidth'
+ " matches 'tabstop', and that 'softtabstop' is off.
+ "
+ if &expandtab
+ setlocal noexpandtab softtabstop=0
+ let &l:shiftwidth = &tabstop
+
+ " If 'expandtab' is not set, we need to set it, and guess an appropriate
+ " 'shiftwidth'.
+ else
+ setlocal expandtab
+
+ " Iterate through the keys of the histogram from smallest to largest.
+ " We'll accept as our 'shiftwidth' the smallest indent level that
+ " constitutes more than 5% of the total lines, configurable by the user.
+ " This is just an heuristic, but it seems to work pretty well.
+ "
+ let shiftwidth = 0
+ let indents = keys(spaces['hist'])
+ call map(indents, 'str2nr(v:val)') " Coerce the string keys to numeric
+ call sort(indents, 's:CompareNumeric') " Force numeric sort
+ for shiftwidth in indents
+ if spaces['hist'][shiftwidth] * 100 / spaces['total']
+ \ >= get(g:, 'detect_indent_confidence', 5)
+ break
+ endif
+ endfor
+
+ " We have our 'shiftwidth'; set it, with 'softtabstop' set to match
+ let &l:shiftwidth = shiftwidth
+ let &l:softtabstop = shiftwidth
+
+ endif
+
+ " Since we just messed with indent settings, stack up a command to revert
+ " the changes when the indent plugin is unloaded, as if we ourselves were
+ " a single filetype indent plugin.
+ "
+ let undo_indent = 'setlocal expandtab< shiftwidth< softtabstop<'
+ if exists('b:undo_indent')
+ let b:undo_indent .= '|' . undo_indent
+ else
+ let b:undo_indent = undo_indent
+ endif
+
+endfunction