trace2: use system/global config for default trace2 settings

Teach git to read the system and global config files for
default Trace2 settings.  This allows system-wide Trace2 settings to
be installed and inherited to make it easier to manage a collection of
systems.

The original GIT_TR2* environment variables are loaded afterwards and
can be used to override the system settings.

Only the system and global config files are used.  Repo and worktree
local config files are ignored.  Likewise, the "-c" command line
arguments are also ignored.  These limits are for performance reasons.

(1) For users not using Trace2, there should be minimal overhead to
detect that Trace2 is not enabled.  In particular, Trace2 should not
allocate lots of otherwise unused data strucutres.

(2) For accurate performance measurements, Trace2 should be initialized
as early in the git process as possible, and before most of the normal
git process initialization (which involves discovering the .git directory
and reading a hierarchy of config files).

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 37 insertions, 5 deletions

diff --git a/t/t0212-trace2-event.sh b/t/t0212-trace2-event.sh
index 028b6c5671..59adae8123 100755
--- a/t/t0212-trace2-event.sh
+++ b/t/t0212-trace2-event.sh
@@ -3,6 +3,11 @@
 test_description='test trace2 facility'
 . ./test-lib.sh
 
+# Turn off any inherited trace2 settings for this test.
+sane_unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT
+sane_unset GIT_TR2_BARE
+sane_unset GIT_TR2_CONFIG_PARAMS
+
 perl -MJSON::PP -e 0 >/dev/null 2>&1 && test_set_prereq JSON_PP
 
 # Add t/helper directory to PATH so that we can use a relative
@@ -17,11 +22,6 @@ PATH="$TTDIR:$PATH" && export PATH
 # Warning: So you may see extra lines in artifact files when
 # Warning: interactively debugging.
 
-# Turn off any inherited trace2 settings for this test.
-unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT
-unset GIT_TR2_BARE
-unset GIT_TR2_CONFIG_PARAMS
-
 V=$(git version | sed -e 's/^git version //') && export V
 
 # There are multiple trace2 targets: normal, perf, and event.
@@ -233,4 +233,36 @@ test_expect_success JSON_PP 'basic trace2_data' '
 	test_cmp expect actual
 '
 
+# Now test without environment variables and get all Trace2 settings
+# from the global config.
+
+test_expect_success JSON_PP 'using global config, event stream, error event' '
+	test_when_finished "rm trace.event actual expect" &&
+	test_config_global trace2.eventTarget "$(pwd)/trace.event" &&
+	test-tool trace2 003error "hello world" "this is a test" &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "003error",
+	|      "hello world",
+	|      "this is a test"
+	|    ],
+	|    "errors":[
+	|      "%s",
+	|      "%s"
+	|    ],
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
 test_done