In commit 8607cd4 of PR git-lfs#3780 we
revised the SmudgeToFile() method of the GitFilter structure in our
"lfs" package to construct an absolute path from its "filename"
parameter and use this path when creating or truncating the file
it creates and populates with the content of a Git LFS object.

We made this change with the goal of resolving the problem reported
in git-lfs#3772 regarding Windows systems where the maximum length of a
file path is often restricted to the MAX_PATH limit of 260 characters.
Beginning with certain versions of Windows 10, system administrators
may now change the maximum file path length to a significantly higher
value, but this change only takes effect for applications which
opt into the new setting.  For reference, see:

  https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation#enable-long-paths-in-windows-10-version-1607-and-later

Since the inclusion of Change List (CL) 32451 in Go version 1.8, many of
the functions and methods in the "os" package of the Go standard library
have supported the use of absolute paths longer than the MAX_PATH limit
on Windows by internally converting such paths into "root local" DOS
device paths before passing them to Windows API system calls.  These
types of DOS device paths begin with a "\\?\" prefix, and are the only
file path format which Windows guarantees will always be accepted even
if they exceed the MAX_PATH length limit:

  https://go.dev/cl/32451
  https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation
  https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#win32-file-namespaces

At the time of our change in PR git-lfs#3780, we were using Go v1.11.1 to build
the Git LFS client.  By changing our SmudgeToFile() method to construct
an absolute path with the Abs() function from the "path/filepath" package
of the Go standard library, we were able to take advantage of the fact
that when we passed the resultant path to the Create() function of the
"os" package, it would translate that path into one beginning with "\\?\"
and thus the final file path could exceed the MAX_PATH length limit.

Note that the Abs() function itself does not convert paths into the
"root local" DOS device format, because it is implemented as a wrapper
around a system call to the GetFullPathName() Windows API function.
That function merges the full path to the current working directory,
which may be a conventional DOS path beginning with a disk designator
like "C:\", to a relative path, and returns the result without converting
it into a DOS device path:

  https://github.com/golang/go/blob/go1.25.3/src/path/filepath/path.go#L162
  https://github.com/golang/go/blob/go1.25.3/src/path/filepath/path_windows.go#L62
  https://github.com/golang/go/blob/go1.25.3/src/syscall/exec_windows.go#L162
  https://learn.microsoft.com/en-ca/windows/win32/api/fileapi/nf-fileapi-getfullpathnamea

However, because our SmudgeToFile() method passed the absolute path
returned by the Abs() function to the Create() function of the "os"
package, our change in PR git-lfs#3780 was effective in allowing file paths
longer than the MAX_PATH limit to be created on Windows, at least in
some cases.  The Create() function, like others in the "os" package,
invokes a chain of internal functions which ultimately pass the input
path to the fixLongPath() function, and that function converts any
absolute path into one beginning with "\\?\":

  https://github.com/golang/go/blob/go1.11.1/src/os/file.go#L274
  https://github.com/golang/go/blob/go1.11.1/src/os/file.go#L284
  https://github.com/golang/go/blob/go1.11.1/src/os/file_windows.go#L158
  https://github.com/golang/go/blob/go1.11.1/src/os/file_windows.go#L97
  https://github.com/golang/go/blob/go1.11.1/src/os/path_windows.go#L131-L209

While the changes in PR git-lfs#3780 resolved some instances where a long
relative path caused errors on Windows when running "git lfs checkout"
or "git lfs pull" commands, they were likely insufficient to resolve
all such cases.

Prior to commit 0cffe93 of our "main"
development branch and commit 2902e9d
of our "release-3.7" branch, the SmudgeToFile() method continued to pass
relative paths to the MkdirAll() function in our "tools" package, which
in turn calls the MkdirAll() function in the "os" package of the standard
Go library.  If the relative path provided to the SmudgeToFile() method
was longer than the MAX_PATH limit even with the trailing file name
removed, and some of the directories named in that path did not exist,
then the MkdirAll() method would have failed, at least with versions of
Go prior to v1.23.0.

Fortunately, ever since commit 70e23fa
of PR git-lfs#5997, when we upgraded the version of Go we use to build the
Git LFS client to Go v1.23.0, this problem and any similar issues should
now be effectively eliminated.  Go v1.23.0 includes the revisions to its
internal fixLongPath() function from CLs (Change Lists) 570995 and 574695,
particularly commits golang/go@2e8d84f
and golang/go@7c89ad6, which ensure
that the function now correctly handles both UNC paths and, most
importantly for our purposes here, relative paths:

  https://go.dev/cl/570995
  https://go.dev/cl/574695
  https://github.com/golang/go/blob/go1.23.0/src/os/path_windows.go#L41-L152

These improvements in the Go standard library therefore apply to our
use of the Remove() and OpenFile() functions from the "os" package in
our SmudgeToFile() method.  Further, they also apply to our use of the
"os" package's Mkdir() function to create any missing directories between
the root of the current Git working tree and the file path provided to
the SmudgeToFile() method.  As noted above, we no longer call the
MkdirAll() function since commits 0cffe93
and 2902e9d.  Instead, the walk() method
of the new DirWalker structure in our "tools" package invokes the Mkdir()
function in the same package for each missing directory, and this
helper function then calls the "os" package's Mkdir() function.

As a consequence, we can simply remove the call to the Abs() function
from our SmudgeToFile() method and use the relative path provided in
its "filename" parameter without any adjustment.

In commit 8607cd4 of PR git-lfs#3780 we
revised the SmudgeToFile() method of the GitFilter structure in our
"lfs" package to construct an absolute path from its "filename"
parameter and use this path when creating or truncating the file
it creates and populates with the content of a Git LFS object.

We made this change with the goal of resolving the problem reported
in git-lfs#3772 regarding Windows systems where the maximum length of a
file path is often restricted to the MAX_PATH limit of 260 characters.
Beginning with certain versions of Windows 10, system administrators
may now change the maximum file path length to a significantly higher
value, but this change only takes effect for applications which
opt into the new setting.  For reference, see:

  https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation#enable-long-paths-in-windows-10-version-1607-and-later

Since the inclusion of Change List (CL) 32451 in Go version 1.8, many of
the functions and methods in the "os" package of the Go standard library
have supported the use of absolute paths longer than the MAX_PATH limit
on Windows by internally converting such paths into "root local" DOS
device paths before passing them to Windows API system calls.  These
types of DOS device paths begin with a "\\?\" prefix, and are the only
file path format which Windows guarantees will always be accepted even
if they exceed the MAX_PATH length limit:

  https://go.dev/cl/32451
  https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation
  https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#win32-file-namespaces

At the time of our change in PR git-lfs#3780, we were using Go v1.11.1 to build
the Git LFS client.  By changing our SmudgeToFile() method to construct
an absolute path with the Abs() function from the "path/filepath" package
of the Go standard library, we were able to take advantage of the fact
that when we passed the resultant path to the Create() function of the
"os" package, it would translate that path into one beginning with "\\?\"
and thus the final file path could exceed the MAX_PATH length limit.

Note that the Abs() function itself does not convert paths into the
"root local" DOS device format, because it is implemented as a wrapper
around a system call to the GetFullPathName() Windows API function.
That function merges the full path to the current working directory,
which may be a conventional DOS path beginning with a disk designator
like "C:\", to a relative path, and returns the result without converting
it into a DOS device path:

  https://github.com/golang/go/blob/go1.25.3/src/path/filepath/path.go#L162
  https://github.com/golang/go/blob/go1.25.3/src/path/filepath/path_windows.go#L62
  https://github.com/golang/go/blob/go1.25.3/src/syscall/exec_windows.go#L162
  https://learn.microsoft.com/en-ca/windows/win32/api/fileapi/nf-fileapi-getfullpathnamea

However, because our SmudgeToFile() method passed the absolute path
returned by the Abs() function to the Create() function of the "os"
package, our change in PR git-lfs#3780 was effective in allowing file paths
longer than the MAX_PATH limit to be created on Windows, at least in
some cases.  The Create() function, like others in the "os" package,
invokes a chain of internal functions which ultimately pass the input
path to the fixLongPath() function, and that function converts any
absolute path into one beginning with "\\?\":

  https://github.com/golang/go/blob/go1.11.1/src/os/file.go#L274
  https://github.com/golang/go/blob/go1.11.1/src/os/file.go#L284
  https://github.com/golang/go/blob/go1.11.1/src/os/file_windows.go#L158
  https://github.com/golang/go/blob/go1.11.1/src/os/file_windows.go#L97
  https://github.com/golang/go/blob/go1.11.1/src/os/path_windows.go#L131-L209

While the changes in PR git-lfs#3780 resolved some instances where a long
relative path caused errors on Windows when running "git lfs checkout"
or "git lfs pull" commands, they were likely insufficient to resolve
all such cases.

Prior to commit 0cffe93 of our "main"
development branch and commit 2902e9d
of our "release-3.7" branch, the SmudgeToFile() method continued to pass
relative paths to the MkdirAll() function in our "tools" package, which
in turn calls the MkdirAll() function in the "os" package of the standard
Go library.  If the relative path provided to the SmudgeToFile() method
was longer than the MAX_PATH limit even with the trailing file name
removed, and some of the directories named in that path did not exist,
then the MkdirAll() method would have failed, at least with versions of
Go prior to v1.23.0.

Fortunately, ever since commit 70e23fa
of PR git-lfs#5997, when we upgraded the version of Go we use to build the
Git LFS client to Go v1.23.0, this problem and any similar issues should
now be effectively eliminated.  Go v1.23.0 includes the revisions to its
internal fixLongPath() function from CLs (Change Lists) 570995 and 574695,
particularly commits golang/go@2e8d84f
and golang/go@7c89ad6, which ensure
that the function now correctly handles both UNC paths and, most
importantly for our purposes here, relative paths:

  https://go.dev/cl/570995
  https://go.dev/cl/574695
  https://github.com/golang/go/blob/go1.23.0/src/os/path_windows.go#L41-L152

These improvements in the Go standard library therefore apply to our
use of the Remove() and OpenFile() functions from the "os" package in
our SmudgeToFile() method.  Further, they also apply to our use of the
"os" package's Mkdir() function to create any missing directories between
the root of the current Git working tree and the file path provided to
the SmudgeToFile() method.  As noted above, we no longer call the
MkdirAll() function since commits 0cffe93
and 2902e9d.  Instead, the walk() method
of the new DirWalker structure in our "tools" package invokes the Mkdir()
function in the same package for each missing directory, and this
helper function then calls the "os" package's Mkdir() function.

As a consequence, we can simply remove the call to the Abs() function
from our SmudgeToFile() method and use the relative path provided in
its "filename" parameter without any adjustment.