It looks like #7738 removed the default unintentionally. This adds it back.
For scripts that `set -u`, this will fail if $INFOPATH is not already set (`INFOPATH: unbound variable`). This provides an empty default, but one that will still satisfy the trailing colon requirement.
It currently switches on `$SHELL`, which points to the user's login shell. However, `shellenv` may be used in contexts where the running shell isn't `$SHELL` (e.g. csh-based `cron` scripts), and Linux desktop environments may set up user sessions in ways that trip up the current algorithm (see #7965 for an example). To work correctly in all circumstances and environments, its output should be determined by the context (calling shell) instead.
Fixes#7965.
The behavior of some programs (e.g., emacs) differs depending on
whether INFOPATH is terminated in a colon or not. For example, the
info viewer built into emacs has a default list of places from which
it will draw info files, and it will only check this if either (a)
INFOPATH is unset, or (b) INFOPATH ends in a colon.
Currently brew shellenv prepends to the existing $INFOPATH and will
separate with a colon if $INFOPATH already exists, but if it does not
it will not terminate in a colon. As a result, info
pages (like emacs and elisp) are missing from the info viewer.
The existing brew shellenv logic used a parameter expansion trick to
include a colon only if it was prepending to an extant INFOPATH, but
because we want brew's contribution to the INFOPATH to always end in a
colon (whether there's an existing INFOPATH or not), we don't have to
use the parameter expansion trick
This commit only changes behavior for "other" shells (i.e., not fish,
csh, or tcsh) since I don't know how to append a colon to variables in
these shells.
$SHELL is set to only the binary name in some environments (e.g. fish, not /usr/bin/fish), causing detection of fish/csh/tsch to fail without this change.
