Issue with Custom_subject Rendering After Update to 6.2.74

[KAZUMA87]

I have been using Sympa's Custom_subject feature with the following configuration:

[% list.name %]:[% list.sequence %]
Previously, emails were sent with subjects like [Sample:1]. However, after updating to version 6.2.74, without making any changes to the configuration, the email subjects have changed to:

[Sample:1][% list.sequence %]
Now, [% list.sequence %] is being displayed literally in the subject line.

I believe this issue is caused by the changes introduced in #1811.

While the sequence number is being correctly incremented and displayed, the [% list.sequence %] placeholder is redundantly appended. I would like the extra [% list.sequence %] to be removed so that the subject returns to the intended format, such as [Sample:1].

Steps to Reproduce:

Configure Custom_subject in Sympa as [% list.name %]:[% list.sequence %].
Send a test email to observe the subject line.
Update Sympa to version 6.2.74.
Send another test email to observe the changed subject line.

Expected Behavior:
The email subject should appear as [Sample:1] without the [% list.sequence %] placeholder.

Actual Behavior: The email subject appears as [Sample:1][% list.sequence %], displaying the placeholder literally.

Additional Information:

Sympa Version: 6.2.74
Suspected Change: #1811

[ikedas]

Hi @KAZUMA87 , thank you for reporting bug!

As a quick fix, could you try this patch?

diff --git a/src/lib/Sympa/Spindle/TransformIncoming.pm b/src/lib/Sympa/Spindle/TransformIncoming.pm
index f88253378..d2ee996bd 100644
--- a/src/lib/Sympa/Spindle/TransformIncoming.pm
+++ b/src/lib/Sympa/Spindle/TransformIncoming.pm
@@ -166,6 +166,7 @@ sub _twist {
             my $subject_field;
             my $re_regexp = Sympa::Regexps::re();
 
+            '' =~ /()/;    # clear $1
             if ($message->{'subject_charset'}) {
                 # Note that Unicode case-ignore match is performed.
                 my $uStem =