def check_deprecated_interp
return unless @deprecated_interp_equivalent
$_sass_deprecated_interp_warnings ||= Set.new
key = [source_range.start_pos.line, source_range.file, @deprecated_interp_equivalent]
return if $_sass_deprecated_interp_warnings.include?(key)
$_sass_deprecated_interp_warnings << key
location = "on line #{source_range.start_pos.line}"
location << " of #{source_range.file}" if source_range.file
Sass::Util.sass_warn "DEPRECATION WARNING \#{location}: \\\#{} interpolation near operators will be simplified\nin a future version of Sass. To preserve the current behavior, use quotes:\n\n \#{@deprecated_interp_equivalent}\n"
end