Introduce `git_fs_path`, which operates on generic filesystem paths. `git_path` will be kept for only git-specific path functionality (for example, checking for `.git` in a path).
libgit2 has two distinct requirements that were previously solved by
`git_buf`. We require:
1. A general purpose string class that provides a number of utility APIs
for manipulating data (eg, concatenating, truncating, etc).
2. A structure that we can use to return strings to callers that they
can take ownership of.
By using a single class (`git_buf`) for both of these purposes, we have
confused the API to the point that refactorings are difficult and
reasoning about correctness is also difficult.
Move the utility class `git_buf` to be called `git_str`: this represents
its general purpose, as an internal string buffer class. The name also
is an homage to Junio Hamano ("gitstr").
The public API remains `git_buf`, and has a much smaller footprint. It
is generally only used as an "out" param with strict requirements that
follow the documentation. (Exceptions exist for some legacy APIs to
avoid breaking callers unnecessarily.)
Utility functions exist to convert a user-specified `git_buf` to a
`git_str` so that we can call internal functions, then converting it
back again.
Ensure that we don't canonicalize symlink targets.
On Windows platforms, we need some logic to emulate symlink(3P) defined by POSIX. As unprivileged symlinks on Windows are a rather new feature, our current implementation is comparatively new and still has some rough edges in special cases. One such case is relative symlinks. While relative symlinks to files in the same directory work as expected, libgit2 currently fails to create reltaive symlinks pointing into other directories. This is due to the fact that we forgot to translate the Unix-style target path to Windows-style. Most importantly, we are currently not converting directory separators from "/" to "\". Fix the issue by calling `git_win32_path_canonicalize` on the target. Add a test that verifies our ability to create such relative links across directories.
The old POSIX regex wrappers have been superseded by our own regexp API that provides a higher-level abstraction. Remove the POSIX wrappers in favor of the new one.
When creating a symlink in Windows, one needs to tell Windows whether the symlink should be a file or directory symlink. To determine which flag to pass, we call `GetFileAttributesW` on the target file to see whether it is a directory and then pass the flag accordingly. The problem though is if create a symlink with a relative target path, then we will check that relative path while not necessarily being inside of the working directory where the symlink is to be created. Thus, getting its attributes will either fail or return attributes of the wrong target. Fix this by resolving the target path relative to the directory in which the symlink is to be created.
Add two more tests to verify that we're not deleting symlink targets, but the symlinks themselves. Furthermore, convert several `cl_skip`s on Win32 to conditional skips depending on whether the clar sandbox supports symlinks or not. Windows is grown up now and may allow unprivileged symlinks if the machine has been configured accordingly.
Several function calls to `p_stat` and `p_close` have no verification if they actually succeeded. As these functions _may_ fail and as we also want to make sure that we're not doing anything dumb, let's check them, too.
By now, we have repeatedly failed to provide a nice cross-platform implementation of `p_fallocate`. Recent tries to do that escalated quite fast to a set of different CMake checks, implementations, fallbacks, etc., which started to look real awkward to maintain. In fact, `p_fallocate` had only been introduced in commit 4e3949b73 (tests: test that largefiles can be read through the tree API, 2019-01-30) to support a test with large files, but given the maintenance costs it just seems not to be worht it. As we have removed the sole user of `p_fallocate` in the previous commit, let's drop it altogether.