Implement a winsymlinks mode that prefers native symlinks, falling back to the deep copy mode
#114
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This adds the missing documentation (in case we ever publish the information about the MSYS variable on msys2.org). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
…llback When native symlinks are available, it is a shame to create deep copies by default. However, since there are many scenarios where symlinks are not available (e.g. when running on FAT, or on older Windows versions, or when Developer Mode is not enabled), we've got to have a fallback. In the regular Cygwin world, it is legitimate to fall back to WSL symlinks and/or to the system file emulation (where a file is created that is marked with the "system" attribute and with content that adheres to a specific, magic form that is recognized specifically by the Cygwin runtime). However, in the world of MSYS2, the assumption is that the result of the operation should be as interoperable with regular Win32 programs as possible. Hence the default to "deepcopy". As a "best of both worlds" mode, let's implement one that tries to create native symlinks by default, and if that fails, uses the "deepcopy" method as a fallback. This addresses msys2#113. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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Cygwin not only had, it still has symlinks like that - except the docs suggest that the
The "shortcut" style links are something different. The new Developer Mode feature is OK, but it's got a big warning on it when you enable it and enterprises therefore don't want to enable it:
https://stackoverflow.com/questions/74613686/what-does-the-warning-in-developer-mode-mean I set |
This mode is incompatible with regular Win32 programs; They won't understand those symlinks and misinterpret them all the time. That is an okay stance to take for Cygwin, which wants you to stay within its ecosystem. It is not an okay stance for MSYS2 which wants to integrate with native Win32 programs as much as possible.
Yes, developer mode comes with a lot of liberties that developing code requires. Nevertheless, it is the mode in which Windows users can create symbolic links in modern Windows without requiring an elevated process (which would increase the security risk a lot more than Developer Mode). In any case, the mode I introduce here, and which I propose to promote to eventually be the default, retains backwards-compatibility in a fashion, by falling back to MSYS2's current behavior if symbolic links cannot be created. |
It surprises new MSYS2 users no end that
ln -sdoes not create symbolic links at all, but deep copies (and with an exit code indicating success!). This did not at all match the expectations of those users who were familiar with Unix' concept of symbolic links and thought that they could rely on MSYS2 providing those, too, or fail with a non-zero exit code.Historical reasons are at play here: When MSYS2 was started (or was that already the behavior of MSys? I forget...), symbolic links were not supported on Windows, at least not really: you had to have administrator privileges to create them (but not to delete them... 🤷) in Windows Vista, and before that, Windows simply had no idea about symbolic links.
So what about Cygwin? Well, Cygwin had something like support for symbolic links, using
.lnkfiles for the emulation. The only problem? You had to stay within Cygwin's walled garden to make use of them. All non-Cygwin applications would react with a less or more unpleasant "huh?!?" when encountering those "symbolic links".That's why MSYS2 chose to deep-copy by default. At least that way
./configurewould still work for those projects that required symbolic links. This was instrumental in getting MSYS2's package ecosystem off the ground.Even when a Windows 10 update introduced support for creating symbolic links without elevation as long as Windows was run in Developer Mode, the created symbolic links are not completely what Unix/Linux/macOS users may be used to, as Windows discerns between directory symlinks and file symlinks.
Be that as it may, now that we've dropped Windows 7 and Windows 8 support, it may be a good time to start switching the default to creating actual symbolic links by default.
Since we still support Windows 8.1 (and a couple of Windows 10 versions that do not allow creating symbolic links in non-elevated operations, even in Developer Mode), we cannot simply switch to a mode where the MSYS2 runtime creates symbolic links when asked for, but we have to have a mode where the MSYS2 runtime first checks whether that is possible with the Windows version on which it is running, and if not, falls back to the deep-copy.
This PR does precisely that: implement that mode, but does not yet flip the default away from
deepcopy. The reason is that I want this to be tested by volunteers (myself included) first, and once it is deemed robust and stable enough, flip the default tonativeordeepcopy.This addresses #113.