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[v4,14/15] git-prompt: prepare for reftable refs backend

Message ID 9df5bc69f971dc2b51d519a2db9a2b0f22f9d87b.1607522430.git.gitgitgadget@gmail.com (mailing list archive)
State New
Headers show
Series reftable library | expand

Commit Message

SZEDER Gábor Dec. 9, 2020, 2 p.m. UTC
From: =?UTF-8?q?SZEDER=20G=C3=A1bor?= <szeder.dev@gmail.com>

In our git-prompt script we strive to use Bash builtins wherever
possible, because fork()-ing subshells for command substitutions and
fork()+exec()-ing Git commands are expensive on some platforms.  We
even read and parse '.git/HEAD' using Bash builtins to get the name of
the current branch [1].  However, the upcoming reftable refs backend
won't use '.git/HEAD' at all, but will write an invalid refname as
placeholder for backwards compatibility instead, which will break our
git-prompt script.

Update the git-prompt script to recognize the placeholder '.git/HEAD'
written by the reftable backend (its content is specified in the
reftable specs), and then fall back to use 'git symbolic-ref' to get
the name of the current branch.

[1] 3a43c4b5bd (bash prompt: use bash builtins to find out current
    branch, 2011-03-31)

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
 contrib/completion/git-prompt.sh | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
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diff --git a/contrib/completion/git-prompt.sh b/contrib/completion/git-prompt.sh
index 4640a1535d1..2e5a5d80271 100644
--- a/contrib/completion/git-prompt.sh
+++ b/contrib/completion/git-prompt.sh
@@ -478,10 +478,15 @@  __git_ps1 ()
 			if ! __git_eread "$g/HEAD" head; then
 				return $exit
-			# is it a symbolic ref?
 			b="${head#ref: }"
 			if [ "$head" = "$b" ]; then
+			elif [ "$b" = "refs/heads/.invalid" ]; then
+				# Reftable
+				b="$(git symbolic-ref HEAD 2>/dev/null)" ||
+				detached=yes
+			fi
+			if [ "$detached" = yes ]; then
 				case "${GIT_PS1_DESCRIBE_STYLE-}" in