Stow walks the package and target tree hierarchies by using mutually
recursive pairs of functions:
- `stow_contents()` and `stow_node()`
- `unstow_contents()` and `unstow_node()`
As Stow runs its planning from the target directory (`plan_*()` both
call `within_target_do()`), previously the parameters for these
included:
- `$target_subpath` (or `$target_subdir` in the `*_node()` functions):
the relative path from the target top-level directory to the target
subdirectory (initially `.` at the beginning of recursion). For
example, this could be `dir1/subdir1/file1`.
- `$source`: the relative path from the target _subdirectory_ (N.B. _not_
top-level directory) to the package subdirectory. For example, if
the relative path to the Stow directory is `../stow`, this could be
`../../../stow/pkg1/dir1/subdir1/file1`. This is used when stowing
to construct a new link, or when unstowing to detect whether the
link can be unstowed.
Each time it descends into a further subdirectory of the target and
package, it appends the new path segment onto both of these, and also
prefixes `$source` with another `..`. When the `--dotfiles` parameter
is enabled, it adjusts `$target_subdir`, performing the `dot-foo` =>
`.foo` adjustment on all segments of the path in one go. In this
case, `$target_subpath` could be something like `.dir1/subdir1/file1`,
and the corresponding `$source` could be something like
`../../../stow/pkg1/dot-dir1/subdir1/file1`.
However this doesn't leave an easy way to obtain the relative path
from the target _top-level_ directory to the package subdirectory
(i.e. `../stow/pkg1/dot-dir1/subdir1/file1`), which is needed for
checking its existence and if necessary iterating over its contents.
The current implementation solves this by including an extra `$level`
parameter which tracks the recursion depth, and uses that to strip the
right number of leading path segments off the front of `$source`.
(In the above example, it would remove `../..`.)
This implementation isn't the most elegant because:
- It involves adding things to `$source` and then removing them again.
- It performs the `dot-` => `.` adjustment on every path segment
at each level, which is overkill, since when recursing down a level,
only adjustment on the final subdirectory is required since the higher
segments have already had any required adjustment.
This in turn requires `adjust_dotfile` to be more complex than it
needs to be.
It also prevents a potential future where we might want Stow to
optionally start iterating from within a subdirectory of the whole
package install image / target tree, avoiding adjustment at higher
levels and only doing it at the levels below the starting point.
- It requires passing an extra `$level` parameter which can be
automatically calculated simply by counting the number of slashes
in `$target_subpath`.
So change the `$source` recursion parameter to instead track the
relative path from the top-level package directory to the package
subdirectory or file being considered for (un)stowing, and rename it
to avoid the ambiguity caused by the word "source".
Also automatically calculate the depth simply by counting the number
of slashes, and reconstruct `$source` when needed by combining the
relative path to the Stow directory with the package name and
`$target_subpath`.
Closes#33.
afa50077c9