Item14256: implemented {LegacyFormfieldNames} flag

... to prevent data loss when upgrading content from 1.x to 2.x

core/lib/Foswiki.spec

@@ -1482,6 +1482,14 @@ $Foswiki::cfg{Store}{filePermission} = 0644;
 # Settings that control the available form fields types. Extensions may extend
 # the set of available types.
 
+# **BOOLEAN LABEL="Enable Legacy Formfield Naming" EXPERT**
+# Enable legacy naming scheme for formfield names. Starting with Foswiki-2.0 formfield names are
+# allowed to contain unicode characters. Before, formfield names have been normalized
+# by stripping these off. If you are upgrading Foswiki from an engine previous to 2.x
+# and your DataForm definitions do contain unicode characters then 
+# you might strongly consider enabling this flag in order to prevent data loss.
+$Foswiki::cfg{LegacyFormfieldNames} = $FALSE;
+
 # **PERL LABEL="Form Types"**
 # This setting is automatically updated by configure to list all the installed
 # FormField types. If you install an extension that adds new Form Field types,

core/lib/Foswiki/Form.pm

@@ -215,8 +215,13 @@ sub fieldTitle2FieldName {
     my ($text) = @_;
     return '' unless defined($text);
     $text =~ s/!//g;
-    $text =~ s/<nop>//g;     # support <nop> character in title
-    $text =~ s/[^\w\.]//g;
+    $text =~ s/<nop>//g;    # support <nop> character in title
+    if ( $Foswiki::cfg{LegacyFormfieldNames} ) {
+        $text =~ s/[^A-Za-z0-9_\.]//g;
+    }
+    else {
+        $text =~ s/[^\w\.]//g;
+    }
     return $text;
 }