Re: [PATCH 39/41] Update shell scripts to compute empty tree object ID

[brian m. carlson]

On Tue, May 01, 2018 at 12:42:57PM +0200, Duy Nguyen wrote:
> On Mon, Apr 23, 2018 at 11:39:49PM +, brian m. carlson wrote:
> > Several of our shell scripts hard-code the object ID of the empty tree.
> > To avoid any problems when changing hashes, compute this value on
> > startup of the script.  For performance, store the value in a variable
> > and reuse it throughout the life of the script.
> > 
> > Signed-off-by: brian m. carlson 
> > ---
> >  git-filter-branch.sh   | 4 +++-
> >  git-rebase--interactive.sh | 4 +++-
> >  templates/hooks--pre-commit.sample | 2 +-
> >  3 files changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/git-filter-branch.sh b/git-filter-branch.sh
> > index 64f21547c1..ccceaf19a7 100755
> > --- a/git-filter-branch.sh
> > +++ b/git-filter-branch.sh
> > @@ -11,6 +11,8 @@
> >  # The following functions will also be available in the commit filter:
> >  
> >  functions=$(cat << \EOF
> > +EMPTY_TREE=$(git hash-object -t tree /dev/null)
> 
> All scripts (except those example hooks) must source
> git-sh-setup. Should we define this in there instead?

I think at this point, I'm okay with special-casing these two uses, but
I would generally say that if we gain any more we should move it there.

There's a trade-off between the benefits of reuse here and the fact that
we're forking a process, which incurs a cost, especially on Windows.

I'm open to hearing other opinions, of course.
-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204


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Re: [PATCH 39/41] Update shell scripts to compute empty tree object ID

[Duy Nguyen]

On Mon, Apr 23, 2018 at 11:39:49PM +, brian m. carlson wrote:
> Several of our shell scripts hard-code the object ID of the empty tree.
> To avoid any problems when changing hashes, compute this value on
> startup of the script.  For performance, store the value in a variable
> and reuse it throughout the life of the script.
> 
> Signed-off-by: brian m. carlson 
> ---
>  git-filter-branch.sh   | 4 +++-
>  git-rebase--interactive.sh | 4 +++-
>  templates/hooks--pre-commit.sample | 2 +-
>  3 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/git-filter-branch.sh b/git-filter-branch.sh
> index 64f21547c1..ccceaf19a7 100755
> --- a/git-filter-branch.sh
> +++ b/git-filter-branch.sh
> @@ -11,6 +11,8 @@
>  # The following functions will also be available in the commit filter:
>  
>  functions=$(cat << \EOF
> +EMPTY_TREE=$(git hash-object -t tree /dev/null)

All scripts (except those example hooks) must source
git-sh-setup. Should we define this in there instead?
--
Duy

[PATCH 39/41] Update shell scripts to compute empty tree object ID

[brian m. carlson]

Several of our shell scripts hard-code the object ID of the empty tree.
To avoid any problems when changing hashes, compute this value on
startup of the script.  For performance, store the value in a variable
and reuse it throughout the life of the script.

Signed-off-by: brian m. carlson 
---
 git-filter-branch.sh   | 4 +++-
 git-rebase--interactive.sh | 4 +++-
 templates/hooks--pre-commit.sample | 2 +-
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index 64f21547c1..ccceaf19a7 100755
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -11,6 +11,8 @@
 # The following functions will also be available in the commit filter:
 
 functions=$(cat << \EOF
+EMPTY_TREE=$(git hash-object -t tree /dev/null)
+
 warn () {
echo "$*" >&2
 }
@@ -46,7 +48,7 @@ git_commit_non_empty_tree()
 {
if test $# = 3 && test "$1" = $(git rev-parse "$3^{tree}"); then
map "$3"
-   elif test $# = 1 && test "$1" = 
4b825dc642cb6eb9a060e54bf8d69288fbee4904; then
+   elif test $# = 1 && test "$1" = $EMPTY_TREE; then
:
else
git commit-tree "$@"
diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 50323fc273..cc873d630d 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -81,6 +81,8 @@ rewritten_pending="$state_dir"/rewritten-pending
 # and leaves CR at the end instead.
 cr=$(printf "\015")
 
+empty_tree=$(git hash-object -t tree /dev/null)
+
 strategy_args=${strategy:+--strategy=$strategy}
 test -n "$strategy_opts" &&
 eval '
@@ -238,7 +240,7 @@ is_empty_commit() {
die "$(eval_gettext "\$sha1: not a commit that can be picked")"
}
ptree=$(git rev-parse -q --verify "$1"^^{tree} 2>/dev/null) ||
-   ptree=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+   ptree=$empty_tree
test "$tree" = "$ptree"
 }
 
diff --git a/templates/hooks--pre-commit.sample 
b/templates/hooks--pre-commit.sample
index 68d62d5446..6a75641638 100755
--- a/templates/hooks--pre-commit.sample
+++ b/templates/hooks--pre-commit.sample
@@ -12,7 +12,7 @@ then
against=HEAD
 else
# Initial commit: diff against an empty tree object
-   against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+   against=$(git hash-object -t tree /dev/null)
 fi
 
 # If you want to allow non-ASCII filenames set this variable to true.