persistence: Serialize persistent data as JSON instead of Perl code.

Will eventually result in one less `eval`, though this change was
actually mostly instigated from a desire to be able to run jq(1) on the
raw data.

modules/ksb/BuildContext.pm

@@ -14,6 +14,7 @@ use File::Basename; # dirname
 use IO::File;
 use POSIX qw(strftime);
 use Errno qw(:POSIX);
+use JSON::PP;
 
 # We derive from ksb::Module so that BuildContext acts like the 'global'
 # ksb::Module, with some extra functionality.
@@ -766,25 +767,30 @@ sub loadPersistentOptions
 
     return unless $fh;
 
+    # $persistent_data should be a JSON object which we can store directly as a
+    # hash.
     my $persistent_data;
     {
         local $/ = undef; # Read in whole file with <> operator.
         $persistent_data = <$fh>;
     }
 
-    # $persistent_data should be Perl code which, when evaluated will give us
-    # a hash called persistent_options which we can then merge into our
-    # persistent options.
-
     my $persistent_options;
 
-    # eval must appear after declaration of $persistent_options
-    eval $persistent_data;
-    if ($@)
-    {
-        # Failed.
-        error ("Failed to read persistent module data: r[b[$@]");
-        return;
+    eval { $persistent_options = decode_json($persistent_data); };
+    if ($@) {
+        # Apparently wasn't JSON, try falling back to old format for compat.
+        # Previously, this was a Perl code which, when evaluated would give
+        # us a hash called persistent_options which we can then merge into our
+        # persistent options.
+        # TODO: Remove compat code after 2018-06-30
+        eval $persistent_data; # Runs Perl code read from file
+        if ($@)
+        {
+            # Failed.
+            error ("Failed to read persistent module data: r[b[$@]");
+            return;
+        }
     }
 
     # We need to keep persistent data with the context instead of with the
@@ -812,6 +818,7 @@ sub storePersistentOptions
     return if pretending();
 
     my $fh = IO::File->new($self->persistentOptionFileName(), '>');
+    my $json = JSON::PP->new->ascii->pretty;
 
     if (!$fh)
     {
@@ -819,10 +826,9 @@ sub storePersistentOptions
         return;
     }
 
-    print $fh "# AUTOGENERATED BY kdesrc-build $SCRIPT_VERSION\n";
+    my $encodedJSON = $json->encode($self->{persistent_options});
 
-    $Data::Dumper::Indent = 1;
-    print $fh Data::Dumper->Dump([$self->{persistent_options}], ["persistent_options"]);
+    print $fh $encodedJSON;
     undef $fh; # Closes the file
 }