[PATCH] git-prompt.sh: Omit prompt for ignored directories

[Jess Austin <jess.austin@gmail.com>]

Introduce a new environmental variable, GIT_PS1_OMITIGNORED, which
tells __git_ps1 to display nothing when the current directory is
set (e.g. via .gitignore) to be ignored by git. In the absence of
GIT_PS1_OMITIGNORED this change has no effect.

Many people manage e.g. dotfiles in their home directory with git.
This causes the prompt generated by __git_ps1 to refer to that "top
level" repo while working in any descendant directory. That can be
distracting, so this patch helps one shut off that noise.

Signed-off-by: Jess Austin <jess.austin@gmail.com>
---
 contrib/completion/git-prompt.sh |  9 +++++++++
 t/t9903-bash-prompt.sh           | 21 +++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/contrib/completion/git-prompt.sh b/contrib/completion/git-prompt.sh
index c5473dc..6a26cb4 100644
--- a/contrib/completion/git-prompt.sh
+++ b/contrib/completion/git-prompt.sh
@@ -84,6 +84,10 @@
 # GIT_PS1_SHOWCOLORHINTS to a nonempty value. The colors are based on
 # the colored output of "git status -sb" and are available only when
 # using __git_ps1 for PROMPT_COMMAND or precmd.
+#
+# If you would like __git_ps1 to do nothing in the case when the current
+# directory is set up to be ignored by git, then set GIT_PS1_OMITIGNORED
+# to a nonempty value.
 
 # check whether printf supports -v
 __git_printf_supports_v=
@@ -501,6 +505,11 @@ __git_ps1 ()
 	local f="$w$i$s$u"
 	local gitstring="$c$b${f:+$z$f}$r$p"
 
+	if [ -n "$(git check-ignore .)" ] && [ -n "${GIT_PS1_OMITIGNORED}" ]
+	then
+		printf_format=""
+	fi
+
 	if [ $pcmode = yes ]; then
 		if [ "${__git_printf_supports_v-}" != yes ]; then
 			gitstring=$(printf -- "$printf_format" "$gitstring")
diff --git a/t/t9903-bash-prompt.sh b/t/t9903-bash-prompt.sh
index 9150984..55bcb6b 100755
--- a/t/t9903-bash-prompt.sh
+++ b/t/t9903-bash-prompt.sh
@@ -35,6 +35,8 @@ test_expect_success 'setup for prompt tests' '
 	git commit -m "another b2" file &&
 	echo 000 >file &&
 	git commit -m "yet another b2" file &&
+	mkdir ignored_dir &&
+	echo "ignored_dir/" >> .gitignore &&
 	git checkout master
 '
 
@@ -588,4 +590,23 @@ test_expect_success 'prompt - zsh color pc mode' '
 	test_cmp expected "$actual"
 '
 
+test_expect_success 'prompt - prompt omitted in ignored directory' '
+	printf "" >expected &&
+	(
+		cd ignored_dir &&
+		GIT_PS1_OMITIGNORED=y &&
+		__git_ps1 >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
+test_expect_success 'prompt - prompt not omitted without GIT_PS1_OMITIGNORED' '
+	printf " (master)" >expected &&
+	(
+		cd ignored_dir &&
+		__git_ps1 >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
 test_done
-- 
1.9.1