Allow --count to accept expressions, just like --grep and --map

- One of the reasons this is useful is you can fetch arbitratily nested items from the data section

- Thanks to Avianna for the suggestion

bin/log-defer-viz

@@ -125,20 +125,15 @@ if ($opt->{'data-only'}) {
 }
 
 
-my $count = {};
-
-foreach my $key (@{ $opt->{count} }) {
-  $count->{$key} = {};
-}
-
 
 my $columns = $opt->{'timer-columns'};
 
 my ($term_cols, $term_rows) = Term::Size::chars(*STDOUT{IO});
 $columns = $term_cols if $term_cols;
 
 
-## The _ sub is a shortcut for use in --grep and --map expressions, ie --grep "_->{data}"
+
+## The _ sub is a shortcut for use in --grep, --map, and --count expressions, ie --grep "_->{data}"
 sub _ () { $_ }
 
 if ($opt->{grep}) {
@@ -152,6 +147,24 @@ if ($opt->{map}) {
 }
 
 
+my $count = {};
+my $count_subs = {};
+
+foreach my $key (@{ $opt->{count} }) {
+  if ($key =~ /^\w+$/) {
+    ## The original format for count arguments were keys to the data hash
+    $count_subs->{$key} = sub { $_[0]->{data}->{$key} };
+  } else {
+    ## But the more general way is with an accessor
+    $count_subs->{$key} = eval('sub { local $_ = $_[0]; ' . $key . '}');
+    die "Error compiling --count expression '$key' ($@)" if $@;
+  }
+
+  $count->{$key} = {};
+}
+
+
+
 unshift(@ARGV, '-') unless @ARGV;
 if (@ARGV > 1 && $opt->{follow}) {
   die "You've specified --follow but have also provided multiple files, which doesn't make sense. Did you mean to do this?";
@@ -266,8 +279,10 @@ sub handle_entry {
 
   if (@{ $opt->{count} }) {
     foreach my $key (@{ $opt->{count} }) {
-      if (exists $entry->{data}->{$key}) {
-        $count->{$key}->{$entry->{data}->{$key}} += 1;
+      my $val = $count_subs->{$key}->($entry);
+
+      if (defined $val) {
+        $count->{$key}->{$val} += 1;
       }
     }