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std: ossymlinks.expandSymlink via reparse-point parsing (#25701)
This PR implements `expandSymlink` on Windows with POSIX readlink
semantics: it expands exactly one hop and returns the stored link target
without resolving the full chain.
The main design question was whether Windows symlink expansion should be
built on path-finalization APIs such as `GetFinalPathNameByHandleW`, or
on direct reparse-point inspection. Current `expandSymlink` is a
single-hop "what target is stored in this link object?" operation and
most of other ways to resolve symlinks on Windows actually try to answer
the "final true file location" question in various slightly-incompatible
ways.
The full final-path resolution on Windows is substantially more complex
than readlink and is planned as a follow-up.
## Implementation choice
Implements Windows `expandSymlink` by:
- opening the path with `FILE_FLAG_OPEN_REPARSE_POINT`
- calling `DeviceIoControl(FSCTL_GET_REPARSE_POINT)`
- parsing the reparse payload for `IO_REPARSE_TAG_SYMLINK` and
`IO_REPARSE_TAG_MOUNT_POINT`
- decoding the UTF-16 slice referenced by the payload
- returning the stored target
This is the right primitive for the API:
- does not depend on whole-path finalization
- works for both symlinks and junctions
- matches the existing Linux behaviour
`widestrs` changes allow using WideCString views without temporary
allocations.
Windows prohibits symlink creation without admin rights, so,
unfortunately, the tests are conditionally skipped by default. Manually
running `testament` in an admin console is required.
## Behaviour:
- One hop only
- Relative symlink targets are returned unchanged
- Absolute Windows targets are converted from stored NT-style prefixes
to usable Win32 forms when applicable
- Non-links, malformed payloads, and unsupported reparse tags raise
`OSError`
## Future work
Path canonicalization, i.e. "final true file location". Which is, BTW,
different from `absolutePath`, which works on paths only and doesn't hit
the underlying FS. So this needs to be an API extension.
I'd like to follow-up with this when I sort through the docs, for now
you can resolve symlinks in a loop.
---------
Co-authored-by: Andreas Rumpf <rumpf_a@web.de>
(cherry picked from commit 00d8f66311)
This commit is contained in:
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@@ -179,7 +179,7 @@ block fileOperations:
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# Symlink handling in `copyFile`, `copyFileWithPermissions`, `copyFileToDir`,
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# `copyDir`, `copyDirWithPermissions`, `moveFile`, and `moveDir`.
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block:
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const symlinksAreHandled = not defined(windows)
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const symlinkCopiesAreHandled = not defined(windows)
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const dname = buildDir/"D20210116T140629"
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const subDir = dname/"sub"
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const subDir2 = dname/"sub2"
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@@ -189,98 +189,131 @@ block fileOperations:
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const brokenSymlinkCopy = brokenSymlink & "_COPY"
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const brokenSymlinkInSubDir = subDir/brokenSymlinkName
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const brokenSymlinkInSubDir2 = subDir2/brokenSymlinkName
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const symlinkProbeTarget = dname/"symlink_probe_target"
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const symlinkProbeLink = dname/"symlink_probe_link"
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createDir(subDir)
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createSymlink(brokenSymlinkSrc, brokenSymlink)
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proc removePathIfExists(path: string) =
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if fileExists(path):
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removeFile(path)
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elif dirExists(path):
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removeDir(path)
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# Test copyFile
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when symlinksAreHandled:
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proc canCreateSymlinks(): bool =
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# We need this check for Windows if we want to permit the block to run
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# when we have admin privileges
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try:
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removePathIfExists(dname)
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createDir(dname)
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writeFile(symlinkProbeTarget, "")
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createSymlink(symlinkProbeTarget, symlinkProbeLink)
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result = true
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except OSError:
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result = false
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finally:
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removePathIfExists(symlinkProbeLink)
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removePathIfExists(symlinkProbeTarget)
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removePathIfExists(dname)
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proc doAssertExpandedSymlink(path, expected: string) =
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let actual = expandSymlink(path)
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doAssert actual == expected,
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"expandSymlink(" & path & ") returned " & actual &
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" instead of " & expected
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removePathIfExists(dname)
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let symlinksAreAvailable = not defined(windows) or canCreateSymlinks()
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if symlinksAreAvailable:
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defer:
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removePathIfExists(dname)
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createDir(subDir)
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createSymlink(brokenSymlinkSrc, brokenSymlink)
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doAssertExpandedSymlink(brokenSymlink, brokenSymlinkSrc)
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doAssertRaises(OSError):
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copyFile(brokenSymlink, brokenSymlinkCopy)
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doAssertRaises(OSError):
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copyFile(brokenSymlink, brokenSymlinkCopy, {cfSymlinkFollow})
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copyFile(brokenSymlink, brokenSymlinkCopy, {cfSymlinkIgnore})
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doAssert not fileExists(brokenSymlinkCopy)
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copyFile(brokenSymlink, brokenSymlinkCopy, {cfSymlinkAsIs})
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when symlinksAreHandled:
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doAssert expandSymlink(brokenSymlinkCopy) == brokenSymlinkSrc
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removeFile(brokenSymlinkCopy)
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else:
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discard expandSymlink(dname)
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# Test copyFile
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when symlinkCopiesAreHandled:
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doAssertRaises(OSError):
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copyFile(brokenSymlink, brokenSymlinkCopy)
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doAssertRaises(OSError):
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copyFile(brokenSymlink, brokenSymlinkCopy, {cfSymlinkFollow})
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copyFile(brokenSymlink, brokenSymlinkCopy, {cfSymlinkIgnore})
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doAssert not fileExists(brokenSymlinkCopy)
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doAssertRaises(AssertionDefect):
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copyFile(brokenSymlink, brokenSymlinkCopy,
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{cfSymlinkAsIs, cfSymlinkFollow})
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copyFile(brokenSymlink, brokenSymlinkCopy, {cfSymlinkAsIs})
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when symlinkCopiesAreHandled:
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doAssertExpandedSymlink(brokenSymlinkCopy, brokenSymlinkSrc)
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removeFile(brokenSymlinkCopy)
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else:
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doAssert not fileExists(brokenSymlinkCopy)
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doAssertRaises(AssertionDefect):
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copyFile(brokenSymlink, brokenSymlinkCopy,
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{cfSymlinkAsIs, cfSymlinkFollow})
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# Test copyFileWithPermissions
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when symlinksAreHandled:
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doAssertRaises(OSError):
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copyFileWithPermissions(brokenSymlink, brokenSymlinkCopy)
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doAssertRaises(OSError):
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copyFileWithPermissions(brokenSymlink, brokenSymlinkCopy,
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options = {cfSymlinkFollow})
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copyFileWithPermissions(brokenSymlink, brokenSymlinkCopy,
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options = {cfSymlinkIgnore})
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doAssert not fileExists(brokenSymlinkCopy)
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copyFileWithPermissions(brokenSymlink, brokenSymlinkCopy,
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options = {cfSymlinkAsIs})
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when symlinksAreHandled:
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doAssert expandSymlink(brokenSymlinkCopy) == brokenSymlinkSrc
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removeFile(brokenSymlinkCopy)
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else:
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doAssert not fileExists(brokenSymlinkCopy)
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doAssertRaises(AssertionDefect):
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# Test copyFileWithPermissions
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when symlinkCopiesAreHandled:
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doAssertRaises(OSError):
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copyFileWithPermissions(brokenSymlink, brokenSymlinkCopy)
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doAssertRaises(OSError):
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copyFileWithPermissions(brokenSymlink, brokenSymlinkCopy,
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options = {cfSymlinkFollow})
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copyFileWithPermissions(brokenSymlink, brokenSymlinkCopy,
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options = {cfSymlinkAsIs, cfSymlinkFollow})
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options = {cfSymlinkIgnore})
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doAssert not fileExists(brokenSymlinkCopy)
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copyFileWithPermissions(brokenSymlink, brokenSymlinkCopy,
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options = {cfSymlinkAsIs})
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when symlinkCopiesAreHandled:
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doAssertExpandedSymlink(brokenSymlinkCopy, brokenSymlinkSrc)
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removeFile(brokenSymlinkCopy)
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else:
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doAssert not fileExists(brokenSymlinkCopy)
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doAssertRaises(AssertionDefect):
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copyFileWithPermissions(brokenSymlink, brokenSymlinkCopy,
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options = {cfSymlinkAsIs, cfSymlinkFollow})
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# Test copyFileToDir
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when symlinksAreHandled:
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doAssertRaises(OSError):
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copyFileToDir(brokenSymlink, subDir)
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doAssertRaises(OSError):
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copyFileToDir(brokenSymlink, subDir, {cfSymlinkFollow})
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copyFileToDir(brokenSymlink, subDir, {cfSymlinkIgnore})
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doAssert not fileExists(brokenSymlinkInSubDir)
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copyFileToDir(brokenSymlink, subDir, {cfSymlinkAsIs})
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when symlinksAreHandled:
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doAssert expandSymlink(brokenSymlinkInSubDir) == brokenSymlinkSrc
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removeFile(brokenSymlinkInSubDir)
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else:
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# Test copyFileToDir
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when symlinkCopiesAreHandled:
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doAssertRaises(OSError):
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copyFileToDir(brokenSymlink, subDir)
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doAssertRaises(OSError):
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copyFileToDir(brokenSymlink, subDir, {cfSymlinkFollow})
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copyFileToDir(brokenSymlink, subDir, {cfSymlinkIgnore})
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doAssert not fileExists(brokenSymlinkInSubDir)
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copyFileToDir(brokenSymlink, subDir, {cfSymlinkAsIs})
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when symlinkCopiesAreHandled:
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doAssertExpandedSymlink(brokenSymlinkInSubDir, brokenSymlinkSrc)
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removeFile(brokenSymlinkInSubDir)
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else:
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doAssert not fileExists(brokenSymlinkInSubDir)
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createSymlink(brokenSymlinkSrc, brokenSymlinkInSubDir)
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createSymlink(brokenSymlinkSrc, brokenSymlinkInSubDir)
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# Test copyDir
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copyDir(subDir, subDir2)
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when symlinksAreHandled:
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doAssert expandSymlink(brokenSymlinkInSubDir2) == brokenSymlinkSrc
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# Test copyDir
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copyDir(subDir, subDir2)
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when symlinkCopiesAreHandled:
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doAssertExpandedSymlink(brokenSymlinkInSubDir2, brokenSymlinkSrc)
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else:
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doAssert not fileExists(brokenSymlinkInSubDir2)
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removeDir(subDir2)
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# Test copyDirWithPermissions
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copyDirWithPermissions(subDir, subDir2)
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when symlinkCopiesAreHandled:
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doAssertExpandedSymlink(brokenSymlinkInSubDir2, brokenSymlinkSrc)
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else:
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doAssert not fileExists(brokenSymlinkInSubDir2)
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removeDir(subDir2)
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# Test moveFile
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moveFile(brokenSymlink, brokenSymlinkCopy)
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doAssertExpandedSymlink(brokenSymlinkCopy, brokenSymlinkSrc)
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removeFile(brokenSymlinkCopy)
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# Test moveDir
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moveDir(subDir, subDir2)
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doAssertExpandedSymlink(brokenSymlinkInSubDir2, brokenSymlinkSrc)
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else:
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doAssert not fileExists(brokenSymlinkInSubDir2)
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removeDir(subDir2)
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# Test copyDirWithPermissions
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copyDirWithPermissions(subDir, subDir2)
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when symlinksAreHandled:
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doAssert expandSymlink(brokenSymlinkInSubDir2) == brokenSymlinkSrc
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else:
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doAssert not fileExists(brokenSymlinkInSubDir2)
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removeDir(subDir2)
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# Test moveFile
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moveFile(brokenSymlink, brokenSymlinkCopy)
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when not defined(windows):
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doAssert expandSymlink(brokenSymlinkCopy) == brokenSymlinkSrc
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else:
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doAssert symlinkExists(brokenSymlinkCopy)
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removeFile(brokenSymlinkCopy)
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# Test moveDir
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moveDir(subDir, subDir2)
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when not defined(windows):
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doAssert expandSymlink(brokenSymlinkInSubDir2) == brokenSymlinkSrc
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else:
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doAssert symlinkExists(brokenSymlinkInSubDir2)
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removeDir(dname)
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discard "Skipping symlink tests: symlink creation is not permitted in this environment"
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block: # moveFile
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let tempDir = getTempDir() / "D20210609T151608"
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