//TODO: and //FIXME: as XCode Warnings

//TODO: and //FIXME: can be turned in warnings during the build phase adding a Run Script Phase to your target’s Build Phases tab.

Then add this shell script code:

echo "searching ${SRCROOT} for ${TAGS}"
find "${SRCROOT}" \( -name "*.swift" \) -print0 | xargs -0 egrep --with-filename --line-number --only-matching "^\s*($TAGS).*\$" | perl -p -e "s/($TAGS)/ warning: \$1/"

The code above is a minor improvement of the solution proposed by Ben Dodson. It will trigger the warning only if the line starts with white spaces.