dylib install_names are presently rewritten relative to HOMEBREW_PREFIX,
except for keg-only formulas, which are rewritten relative to
opt_prefix.
If we make a formula keg_only, all of its dependents need to be bumped,
since it will no longer exist in HOMEBREW_PREFIX and all of the links
will be written incorrectly.
If we always use opt_prefix, we avoid that dilemma, and make installed
packages more robust if a dependency is `brew unlink`ed.
ClosesHomebrew/homebrew#43518.
Signed-off-by: Dominyk Tiller <dominyktiller@gmail.com>
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