trace: disable additional trace output for unit tests

Some unit-tests use trace output to verify internal state, and unstable
output such as timestamps and line numbers are not useful there.

Disable additional trace output if GIT_TRACE_BARE is set.

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -109,6 +109,10 @@ export GIT_AUTHOR_EMAIL GIT_AUTHOR_NAME
 export GIT_COMMITTER_EMAIL GIT_COMMITTER_NAME
 export EDITOR
 
+# Tests using GIT_TRACE typically don't want <timestamp> <file>:<line> output
+GIT_TRACE_BARE=1
+export GIT_TRACE_BARE
+
 if test -n "${TEST_GIT_INDEX_VERSION:+isset}"
 then
 	GIT_INDEX_VERSION="$TEST_GIT_INDEX_VERSION"

trace.c

@@ -87,11 +87,17 @@ static const char err_msg[] = "Could not trace into fd given by "
 
 static int prepare_trace_line(struct trace_key *key, struct strbuf *buf)
 {
+	static struct trace_key trace_bare = TRACE_KEY_INIT(BARE);
+
 	if (!trace_want(key))
 		return 0;
 
 	set_try_to_free_routine(NULL);	/* is never reset */
 
+	/* unit tests may want to disable additional trace output */
+	if (trace_want(&trace_bare))
+		return 1;
+
 	/* add line prefix here */
 
 	return 1;