MDEV-26102 dgcov: add support for *.gcda.gcov.json.gz files of gcov 9.1+

- Script covers situation for gcov (gcc) < 9 with non-json format of
generated files as well as for gcov (gcc) >=8 with json generated format

Reviewed by: serg@mariadb.com

mysql-test/dgcov.pl

@@ -62,13 +62,16 @@ my $res;
 my $cmd;
 if ($opt_purge)
 {
-  $cmd= "find . -name '*.da' -o -name '*.gcda' -o -name '*.gcov' -o ".
+  $cmd= "find . -name '*.da' -o -name '*.gcda*' -o -name '*.gcov' -o ".
                "-name '*.dgcov' | grep -v 'README\.gcov' | xargs rm -f ''";
   logv "Running: $cmd";
   system($cmd)==0 or die "system($cmd): $? $!";
   exit 0;
 }
 
+my $gcc_version= `gcc -dumpversion`;
+$gcc_version=~ s/(\d).*$/$1/;
+
 find(\&gcov_one_file, $root);
 find(\&write_coverage, $root) if $opt_generate;
 exit 0 if $opt_only_gcov;
@@ -162,6 +165,7 @@ sub gcov_one_file {
   }
 
   # now, read the generated file
+  if ($gcc_version <9){
     for my $gcov_file (<$_*.gcov>) {
       open FH, '<', "$gcov_file" or die "open(<$gcov_file): $!";
       my $fname;
@@ -183,6 +187,20 @@ sub gcov_one_file {
       }
       close(FH);
     }
+  } else {
+    use IO::Uncompress::Gunzip qw(gunzip $GunzipError);
+    use JSON::PP;
+    my $gcov_file_json;
+    my $fname;
+    gunzip "$_.gcov.json.gz" => \$gcov_file_json or die "gunzip($_.gcov.json.gz): $GunzipError";
+    my $obj= decode_json $gcov_file_json;
+    for my $file (@{$obj->{files}}) {
+      $fname= $file->{file};
+      for my $line (@{$file->{lines}}){
+        $cov{$fname}->{$line->{line_number}}+= $line->{count};
+      }
+    }
+  }
 }
 
 sub write_coverage {