good patch vs. sed fixes

Hi all,

I'm not sure it is worth the effort, but from time to time I stumble 
across the "problem" that certain sed or patch commands would apply 
multiple times although they should not. I'm fully aware this is 
unsupported "deviating from the book" but it happens. I'm trying to build 
some not-yet-in-the-book new version, something fails, I fix the problem 
and try again, then some unexpected "double sed" or "double patch" 
silently breaks stuff. Sure, I should have done it cleanly from scratch, 
but the nature of the fixed problem suggested I could just repeat the 
build...

Current example: I was upgrading to icu-76.1 . icu is an ugly package that 
usually triggers having to rebuild quite a number of others. firefox is 
one of those, at least when using system-icu. I'm aware the book stays 
with firefox ESR versions for a reason, however, if I'm rebuilding it 
anyway, I (try to) use the most recent release version. The ICU74+ sed for 
firefox in the book fixes the build problem just fine, BUT it would apply 
arbitrarily often. Took me quite some time to understand that my 
firefox-132 problem is NOT icu-76.1 but applying the system-icu sed 
multiple times.

My personal solution for that is protecting my build script like this:
grep -q "CLASS_CHARACTER,CLASS_CHARACTER" intl/lwbrk/LineBreaker.cpp || 
for i in {43..47}; do
    sed '/ZWJ/s/}/,CLASS_CHARACTER&/' -i intl/lwbrk/LineBreaker.cpp
done

I do like the idea to fix stuff with a simple sed if it helps avoiding a 
patch, BUT only if it does the job similarily well. I kind of appreciate 
the educational value of a sophisticated sed, but in my experience 
a unified patch is less likely to "doubly apply" (though it happened to me 
before) and sometimes makes clearer what actually needs to be changed.

I'm not proposing using some more official patch such as 
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=d9712b1358dc1b64933c3090d72153aae3270f25 
in this case, I'd just like to mention that this patch 1) makes the 
idea more clear (there are not just 5 more CLASS_CHARACTERs but they do 
have names) and it does not apply multiple times...

Regards
Uwe

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