fsmonitor: update GIT_TEST_FSMONITOR support

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.

Remove the outdated instructions on how to run the test suite utilizing
fsmonitor now that it is properly documented in t/README.

Signed-off-by: Ben Peart <Ben.Peart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

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;

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
 ------------
 

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 &&

t/t7519-status-fsmonitor.sh

@@ -4,13 +4,6 @@ test_description='git status with file system watcher'
 
 . ./test-lib.sh
 
-#
-# 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.
-#
-
 # Note, after "git reset --hard HEAD" no extensions exist other than 'TREE'
 # "git update-index --fsmonitor" can be used to get the extension written
 # before testing the results.

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 ||