[PATCH v2 0/2] mv: report missing destination leading directory

["Lucas Zamboni Orioli via GitGitGadget" <gitgitgadget@gmail.com>]

Changes since v1:

 * altered the error message to include both source and destination as
   suggested by Ben Knoble

Lucas Zamboni Orioli (2):
  mv: name both source and destination when rename fails
  mv: check for missing destination directory before renaming

 builtin/mv.c  | 23 ++++++++++++++++++++++-
 t/t7001-mv.sh | 14 ++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)


base-commit: 9a0c4701dcd5725c4184599322b52933ff5005ca
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2356%2FZamboniL%2Fmv-detect-non-existing-target-folder-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2356/ZamboniL/mv-detect-non-existing-target-folder-v2
Pull-Request: https://github.com/git/git/pull/2356

Range-diff vs v1:

 -:  ---------- > 1:  0d67da588b mv: name both source and destination when rename fails
 1:  692f44456f ! 2:  1a790e0016 mv: report missing destination leading directory
     @@ Metadata
      Author: Lucas Zamboni Orioli <lucaszam0@gmail.com>
      
       ## Commit message ##
     -    mv: report missing destination leading directory
     +    mv: check for missing destination directory before renaming
      
     -    When moving a file to a destination whose leading directory does not
     -    exist, "git mv" fails at the rename(2) syscall with ENOENT. Because
     -    the error is reported via die_errno() using only the source path:
     +    Moving a file into a directory that does not exist fails at rename(2)
     +    with ENOENT. The checking phase already rejects a missing destination
     +    directory when the destination ends in a slash, but a destination that
     +    names a file inside a non-existent directory is not caught and only
     +    fails later at the syscall. As a consequence "git mv -n" does not
     +    detect the problem either: the dry run never reaches rename(2) and
     +    reports a move that would not actually succeed.
      
     -        fatal: renaming 'src' failed: No such file or directory
     +    Detect this during the checking phase. For entries that will be renamed
     +    on disk, stat the destination's leading directory and, if it is
     +    missing, fail with the existing "destination directory does not exist"
     +    message. Guard the check with the same condition under which rename(2)
     +    is invoked, so that directory moves, whose child entries are expanded
     +    to paths under a not-yet-created directory, and sparse or out-of-cone
     +    destinations, which are not written to the worktree, are not flagged
     +    incorrectly.
      
     -    the message misleadingly blames the source, even though it is the
     -    destination's parent directory that is missing. A user who runs
     +    This is a best-effort diagnostic rather than a guarantee: the
     +    destination directory can still disappear between the check and the
     +    rename(2). It fixes the common case and, unlike the syscall path,
     +    lets "git mv -n" report the failure.
      
     -        git mv a/file b/does-not-exist/file
     -
     -    is told the problem is with 'a/file', which exists, giving no hint
     -    that 'b/does-not-exist/' needs to be created first.
     -
     -    The checking phase already rejects a missing destination directory
     -    when the destination ends in a slash, but a destination that names a
     -    file inside a non-existent directory is not caught and only fails
     -    later at rename(2). As a result "git mv -n" also fails to detect the
     -    problem, since the dry run never reaches the syscall and reports a
     -    move that would not actually succeed.
     -
     -    Detect this during the checking phase instead: for entries that will
     -    be renamed on disk, stat the destination's leading directory and, if
     -    it is missing, fail with the existing "destination directory does not
     -    exist" message. Guard the check with the same condition under which
     -    rename(2) is invoked so that directory moves, whose child entries are
     -    expanded to paths under a not-yet-created directory, and sparse or
     -    out-of-cone destinations, which are not written to the worktree, are
     -    not flagged incorrectly.
     -
     -    This gives a clear message and lets "git mv -n" report the failure.
     +    Add tests covering both the error path and the dry-run detection.
      
          Signed-off-by: Lucas Zamboni Orioli <lucaszam0@gmail.com>
      

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