This requires threading environment_t through many places, such as completions
and history. We introduce null_environment_t for when the environment isn't
important.
If the user is in a directory which has been unlinked, it is possible
for the path .. to not exist, relative to the working directory.
Always pass in the working directory (potentially virtual) to
path_get_cdpath; this ensures we check absolute paths and are immune
from issues if the working directory has been unlinked.
Also introduce a new function path_normalize_for_cd which normalizes the
"join point" of a path and a working directory. This allows us to 'cd' out of
a non-existent directory, but not cd into such a directory.
Fixes#5341
This switches fish to a "virtual" PWD, where it no longer uses getcwd to
discover its PWD but instead synthesizes it based on normalizing cd against
the $PWD variable.
Both pwd and $PWD contain the virtual path. pwd is taught about -P to
return the physical path, and -L the logical path (which is the default).
Fixes#3350
This eliminates the "missing" notion of env_var_t. Instead
env_get returns a maybe_t<env_var_t>, which forces callers to
handle the possibility that the variable is missing.
Internally fish should store vars as a vector of elements. The current
flat string representation is a holdover from when the code was written
in C.
Fixes#4200
This is the first step to implementing issue #4200 is to stop subclassing
env_var_t from wcstring. Not too surprisingly doing this identified
several places that were incorrectly treating env_var_t and wcstring as
interchangeable types. I'm not talking about those places that passed
an env_var_t instance to a function that takes a wcstring. I'm talking
about doing things like assigning the former to the latter type, relying
on the implicit conversion, and thus losing information.
We also rename `env_get_string()` to `env_get()` for symmetry with
`env_set()` and to make it clear the function does not return a string.
