I have been caught out twice by packages suddenly failing to do what I want after an emerge. e.g. Amarok stopped playing mp3s because some mp3 flag had been added to xine-lib since it had been updated, that had to be enabled in order to play mp3s. Solution: warn the user when USE flags have been added or changed since the last previously installed version of that package (if any) on the computer. This warning would obviously have to appear when the package was emerge for the first time or when it was updated. Thanks.
emerge -pv already highlights added/removed flags.
That doesn't help. A typical Gentoo user will not be willing to do emerge -pv before EVERY time they emerge packages. This information about new USE flags should be collected and automatically displayed to the user every time emerge has finished emerging new packages, perhaps using the yellow warning text.
EMERGE_DEFAULT_OPTS="--ask" without using --verbose will pretty much give you what you want. Even when not using --verbose, changed and new USE flags will still be shown so scanning the package list for interesting changes becomes very quick. If you want _only_ new flags listed, create a small (2-line) script that greps for 'USE=.*%' before running the actual emerge command.
Fair enough. Doesn't look like there's an easy way around this. I'll try your method anyway.
