[PATCH v2 3/5] fsmonitor: update GIT_TEST_FSMONITOR support

[Ben Peart <benpeart@microsoft.com>]

Rename GIT_FSMONITOR_TEST to GIT_TEST_FSMONITOR for consistency with the
other GIT_TEST_ special setups and properly document its use.

Add logic in t/test-lib.sh to give a warning when the old variable is set to
let people know they need to update their environment to use the new
variable.

Signed-off-by: Ben Peart <Ben.Peart@microsoft.com>
---
 config.c                    |  2 +-
 t/README                    |  4 ++++
 t/t1700-split-index.sh      |  2 +-
 t/t7519-status-fsmonitor.sh |  2 +-
 t/test-lib.sh               | 20 ++++++++++++++++++++
 5 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/config.c b/config.c
index 3461993f0a..3555c63f28 100644
--- a/config.c
+++ b/config.c
@@ -2278,7 +2278,7 @@ int git_config_get_max_percent_split_change(void)
 int git_config_get_fsmonitor(void)
 {
 	if (git_config_get_pathname("core.fsmonitor", &core_fsmonitor))
-		core_fsmonitor = getenv("GIT_FSMONITOR_TEST");
+		core_fsmonitor = getenv("GIT_TEST_FSMONITOR");
 
 	if (core_fsmonitor && !*core_fsmonitor)
 		core_fsmonitor = NULL;
diff --git a/t/README b/t/README
index 56a417439c..47165f7eab 100644
--- a/t/README
+++ b/t/README
@@ -319,6 +319,10 @@ GIT_TEST_OE_DELTA_SIZE=<n> exercises the uncommon pack-objects code
 path where deltas larger than this limit require extra memory
 allocation for bookkeeping.
 
+GIT_TEST_FSMONITOR=$PWD/t7519/fsmonitor-all exercises the fsmonitor
+code path for utilizing a file system monitor to speed up detecting
+new or changed files.
+
 Naming Tests
 ------------
 
diff --git a/t/t1700-split-index.sh b/t/t1700-split-index.sh
index b3b4d83eaf..f6a856f24c 100755
--- a/t/t1700-split-index.sh
+++ b/t/t1700-split-index.sh
@@ -6,7 +6,7 @@ test_description='split index mode tests'
 
 # We need total control of index splitting here
 sane_unset GIT_TEST_SPLIT_INDEX
-sane_unset GIT_FSMONITOR_TEST
+sane_unset GIT_TEST_FSMONITOR
 
 test_expect_success 'enable split index' '
 	git config splitIndex.maxPercentChange 100 &&
diff --git a/t/t7519-status-fsmonitor.sh b/t/t7519-status-fsmonitor.sh
index 756beb0d8e..d77012ea6d 100755
--- a/t/t7519-status-fsmonitor.sh
+++ b/t/t7519-status-fsmonitor.sh
@@ -8,7 +8,7 @@ test_description='git status with file system watcher'
 # To run the entire git test suite using fsmonitor:
 #
 # copy t/t7519/fsmonitor-all to a location in your path and then set
-# GIT_FSMONITOR_TEST=fsmonitor-all and run your tests.
+# GIT_TEST_FSMONITOR=fsmonitor-all and run your tests.
 #
 
 # Note, after "git reset --hard HEAD" no extensions exist other than 'TREE'
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 44288cbb59..653688c067 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -140,6 +140,26 @@ then
 	export GIT_INDEX_VERSION
 fi
 
+check_var_migration () {
+	old_name=$1 new_name=$2
+	eval "old_isset=\${${old_name}:+isset}"
+	eval "new_isset=\${${new_name}:+isset}"
+	case "$old_isset,$new_isset" in
+	isset,)
+		echo >&2 "warning: $old_name is now $new_name"
+		echo >&2 "hint: set $new_name too during the transition period"
+		eval "$new_name=\$$old_name"
+		;;
+	isset,isset)
+		# do this later
+		# echo >&2 "warning: $old_name is now $new_name"
+		# echo >&2 "hint: remove $old_name"
+		;;
+	esac
+}
+
+check_var_migration GIT_FSMONITOR_TEST GIT_TEST_FSMONITOR
+
 # Add libc MALLOC and MALLOC_PERTURB test
 # only if we are not executing the test with valgrind
 if expr " $GIT_TEST_OPTS " : ".* --valgrind " >/dev/null ||
-- 
2.18.0.windows.1