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[PATCH] t/perf: depend on perl JSON only when using --codespeed

Commit 05eb1c37ed (perf/aggregate: implement codespeed JSON output,
2018-01-05) added a dependency on the perl JSON module to show output
from aggregate.perl, but we only need it when the user asks for
--codespeed output. While the module is pretty common, it's not part of
the base system, and this dependency can get in the way of producing the
default human-readable output.

Let's bump the "use" down to a "require" in the code path that needs it,
which will be interpreted at run-time instead of compile-time. People
not using "--codespeed" won't even load the module, and anybody using it
should see the same results (including the same perl error if they don't
have it).

Note that this skips the importing step, so we'll have to fully qualify
our function call. We could accomplish the same thing in other ways.
E.g., calling JSON->import() ourselves, or wrapping "use JSON" in an
eval. Since there's only one such call, this seems like the
least-magical way of doing it.

Signed-off-by: Jeff King <peff@xxxxxxxx>
This bites me occasionally when running perf tests on many-core work
machines where I can't just "apt-get install libjson-perl". So I finally
decided look into it. :)

 t/perf/aggregate.perl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/t/perf/aggregate.perl b/t/perf/aggregate.perl
index 494907a892..76dd48f890 100755
--- a/t/perf/aggregate.perl
+++ b/t/perf/aggregate.perl
@@ -3,7 +3,6 @@
 use lib '../../perl/build/lib';
 use strict;
 use warnings;
-use JSON;
 use Getopt::Long;
 use Git;
@@ -342,7 +341,8 @@ sub print_codespeed_results {
-	print to_json(\@data, {utf8 => 1, pretty => 1, canonical => 1}), "\n";
+	require JSON;
+	print JSON::to_json(\@data, {utf8 => 1, pretty => 1, canonical => 1}), "\n";
 binmode STDOUT, ":utf8" or die "PANIC on binmode: $!";