patchp4: fix "Not a valid object name HEAD0" when unshelving

git p4 unshelve was failing with "fatal: Not a valid object name HEAD0" and "Command failed: git cat-file commit HEAD^0" on certain systems e.g. git version 2.21.0.windows.1 + python 2.7.16

It seems that certain python pOpen implementations drop the ^ character when invoked using a string instead of an array as first argument, which is what is done by extractLogMessageFromGitCommit.

Solution is to use the array format of passing the command to fOpen, which is preferred (see https://docs.python.org/2/library/subprocess.html) and is used in other parts of this code anyway.

Mike Mueller (1):
  p4 unshelve: fix "Not a valid object name HEAD0"

 git-p4.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

base-commit: aeb582a98374c094361cba1bd756dc6307432c42
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-183%2Fmdymike%2Fmaint-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-183/mdymike/maint-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/183

From: Mike Mueller <mike.mueller@moodys.com>

git p4 unshelve was failing with these errors on Windows:

fatal: Not a valid object name HEAD0 Command failed: git cat-file commit HEAD^0

(git version 2.21.0.windows.1, python 2.7.16)

The pOpen call used by git-p4 to invoke the git command can take either a string or an array as a first argument. The array form is preferred however the extractLogMessageFromGitCommit method was using the string form, which makes the caller responsible for escaping the command text appropriately (see https://docs.python.org/2/library/subprocess.html)

Somewhat ironically, the carat character is the escape character in Windows and so should be escaped (HEAD^^0). Without the extra carat, the OS was passing an escaped 0 to the git command instead, and the git command was rejecting the invalid object name "HEAD0"

The behaviour can be confirmed by typing ECHO HEAD^0 at the command- prompt, which emits HEAD0.

The solution is simply to use the array format of passing the command to fOpen, which is preferred and used in other parts of this code anyway.

Signed-off-by: Mike Mueller <mike.mueller@moodys.com>
---
 git-p4.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

"Mike Mueller via GitGitGadget" <gitgitgadget@gmail.com> writes:

Rewrite the sentence that begin with "The array form is preferred...", as it is somewhat unreadable. "X is preferred because Y; however Z was using the other one" would be understandable.

s/carat/caret/ everywhere.

git p4 unshelve was failing with "fatal: Not a valid object name HEAD0" and "Command failed: git cat-file commit HEAD^0" on certain systems e.g. git version 2.21.0.windows.1 + python 2.7.16

It seems that certain python pOpen implementations drop the ^ character when invoked using a string instead of an array as first argument, which is what is done by extractLogMessageFromGitCommit.

Solution is to use the array format of passing the command to fOpen, which is preferred (see https://docs.python.org/2/library/subprocess.html) and is used in other parts of this code anyway.

Mike Mueller (1):
  p4 unshelve: fix "Not a valid object name HEAD0" on Windows

 git-p4.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

base-commit: aeb582a98374c094361cba1bd756dc6307432c42
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-183%2Fmdymike%2Fmaint-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-183/mdymike/maint-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/183

Range-diff vs v1:

 1:  fc580e902b ! 1:  5e89d1aceb p4 unshelve: fix "Not a valid object name HEAD0"
     @@ -1,8 +1,8 @@
      Author: Mike Mueller <mike.mueller@moodys.com>
      
     -    p4 unshelve: fix "Not a valid object name HEAD0"
     +    p4 unshelve: fix "Not a valid object name HEAD0" on Windows
      
     -    git p4 unshelve was failing with these errors on Windows:
     +    git p4 unshelve was failing with these errors:
      
          fatal: Not a valid object name HEAD0
          Command failed: git cat-file commit HEAD^0
     @@ -10,21 +10,19 @@
          (git version 2.21.0.windows.1, python 2.7.16)
      
          The pOpen call used by git-p4 to invoke the git command can take either a
     -    string or an array as a first argument.  The array form is preferred
     -    however the extractLogMessageFromGitCommit method was using the string
     -    form, which makes the caller responsible for escaping the command text
     -    appropriately (see https://docs.python.org/2/library/subprocess.html)
     -
     -    Somewhat ironically, the carat character is the escape character in
     -    Windows and so should be escaped (HEAD^^0).  Without the extra carat, the
     -    OS was passing an escaped 0 to the git command instead, and the git
     -    command was rejecting the invalid object name "HEAD0"
     +    string or an array as a first argument. The array form is preferred
     +    because platform-specific escaping of special characters will be
     +    handled automatically.(https://docs.python.org/2/library/subprocess.html)
     +    The extractLogMessageFromGitCommit method was, however, using the string
     +    form and so the caret (^) character in the HEAD^0 argument was not being
     +    escaped on Windows.  The caret happens to be the escape character, which
     +    is why the git command was receiving HEAD0.
      
          The behaviour can be confirmed by typing ECHO HEAD^0 at the command-
          prompt, which emits HEAD0.
      
          The solution is simply to use the array format of passing the command to
     -    fOpen, which is preferred and used in other parts of this code anyway.
     +    fOpen, which is recommended and used in other parts of this code anyway.
      
          Signed-off-by: Mike Mueller <mike.mueller@moodys.com>
      

From: Mike Mueller <mike.mueller@moodys.com>

git p4 unshelve was failing with these errors:

fatal: Not a valid object name HEAD0 Command failed: git cat-file commit HEAD^0

(git version 2.21.0.windows.1, python 2.7.16)

The pOpen call used by git-p4 to invoke the git command can take either a string or an array as a first argument. The array form is preferred because platform-specific escaping of special characters will be handled automatically.(https://docs.python.org/2/library/subprocess.html) The extractLogMessageFromGitCommit method was, however, using the string form and so the caret (^) character in the HEAD^0 argument was not being escaped on Windows. The caret happens to be the escape character, which is why the git command was receiving HEAD0.

The behaviour can be confirmed by typing ECHO HEAD^0 at the command- prompt, which emits HEAD0.

The solution is simply to use the array format of passing the command to fOpen, which is recommended and used in other parts of this code anyway.

Signed-off-by: Mike Mueller <mike.mueller@moodys.com>
---
 git-p4.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

"Mike Mueller via GitGitGadget" <gitgitgadget@gmail.com> writes:

In the output from

    git grep 'read_pipe_lines("'

together with a few hits to harmless constant command line, we find this line

    diff = read_pipe_lines("git diff-tree -r %s \"%s^\" \"%s\"" % (self.diffOpts, id, id))

Would the caret we see there cause a similar problem? It would end up running something like

   $ git diff-tree -r -M "HEAD^" "HEAD"

Hi Junio,

On Tue, 28 May 2019, Junio C Hamano wrote:

I think you're right!

In addition, I wonder whether we would want to replace the `^` by a `~`, which would have the same effect, but does not need quoting in Bash nor CMD.

Ciao, Dscho