build-sys: fix update-potfiles script

Now are using "git ls-files" to avoid finding non-project
files or autoheaders which could break the dist tarball.

For non-git source dirs we assume that any existing POTFILES.in is
up-todate (build from tarball) or we provide at least an empty list
to not be a show-stopper for builds from poor "git archive".

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>

po/update-potfiles

@@ -3,16 +3,38 @@
 # Copyright (C) 2009 Karel Zak <kzak@redhat.com>
 #
 
-# find all *.c files, 
+# find all git-tracked and existing *.c and *.h files
+# exclude some (sub)directories
 # sort the list
-# exclude /samples/ subdirectories
-# exclude ./tests/ from the list 
-#         and remove "./" prefix
 
-[ ! -f "po/Makevars" ] && \
-	echo "You must run this script in the top-level directory"
+if [ ! -f "po/Makevars" ]; then
+	echo "error: update-potfiles must run in the top-level directory" >&2
+	exit 1
+fi
 
-find -name "*.c" -or -name "*.h" | \
-  sort | \
-  sed '/samples/d; /config\.h/d; /util-linux-.*/d; /\.\/tests/d; s/^\.\///' \
-  > po/POTFILES.in
+# find all git-tracked files
+source_files=$(git ls-files . 2>/dev/null)
+if [ $? -ne 0 ] || [ -z "$source_files" ]; then
+	echo "$0: warning: update-potfiles requires git" >&2
+	# we still go through the rest of this script to provide at least an empty
+	# list or remove non-existing (deleted) files
+	source_files=$(cat po/POTFILES.in 2>/dev/null)
+fi
+
+# apply include/exclude patterns
+source_files=$(
+	echo "$source_files" \
+	| sed \
+		-e '/\(\.h\|\.c\)$/!d' \
+		-e '/^tests\//d' \
+		-e '/\/samples\//d' \
+)
+
+# throw away non-existing files (dirty git repo)
+echo "$source_files" \
+	| xargs -r find 2>/dev/null \
+	| sort \
+	> po/POTFILES.in
+
+# if this script is broken then we have probably an empty list
+[ -s po/POTFILES.in ] || echo "$0: warning: po/POTFILES.in is empty" >&2