/usr/share/fish/functions/mimedb.fish is in fish-common 2.2.0-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12  | # Wrap mimedb in a function so it does not have to be found in PATH
# But only if it's installed
if test -x $__fish_bin_dir/mimedb
	eval "function mimedb --description 'Look up file information via the mimedb database'
	         \"$__fish_bin_dir/mimedb\" \$argv
	      end"
else
	function mimedb --description 'Look up file information via the mimedb database'
		# Create a function that simply fails, because mimedb not installed
		return 1
	end
end
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