From b949215732ea8a1f0f61f85a9b0d49425321bd25 Mon Sep 17 00:00:00 2001
From: Steve Hancock <perltidy@users.sourceforge.net>
Date: Tue, 10 Aug 2021 08:41:42 -0700
Subject: [PATCH] Fix formatting instability, b1192

---
 dev-bin/run_convergence_tests.pl.data | 18 ++++++++++++++++++
 lib/Perl/Tidy/Formatter.pm            | 13 +++++++++++--
 local-docs/BugLog.pod                 | 22 ++++++++++++++++++++++
 3 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/dev-bin/run_convergence_tests.pl.data b/dev-bin/run_convergence_tests.pl.data
index fc38ffa3..46e7d511 100644
--- a/dev-bin/run_convergence_tests.pl.data
+++ b/dev-bin/run_convergence_tests.pl.data
@@ -7121,6 +7121,24 @@ print
 --paren-vertical-tightness=1
 --weld-nested-containers
 
+==> b1192.in <==
+# S1
+          @EXPORT =
+              ( @{$EXPORT_TAGS{standard}}, );
+
+# S2
+          @EXPORT = (
+                      @{$EXPORT_TAGS{standard}},
+          );
+
+==> b1192.par <==
+--brace-tightness=2
+--continuation-indentation=4
+--ignore-old-breakpoints
+--indent-columns=10
+--line-up-parentheses
+--maximum-line-length=48
+
 ==> b120.in <==
 # Same as bug96
 # State 1
diff --git a/lib/Perl/Tidy/Formatter.pm b/lib/Perl/Tidy/Formatter.pm
index c49060b0..71e36532 100644
--- a/lib/Perl/Tidy/Formatter.pm
+++ b/lib/Perl/Tidy/Formatter.pm
@@ -16029,6 +16029,13 @@ sub set_continuation_breaks {
         my $bp_count           = 0;
         my $do_not_break_apart = 0;
 
+        # Do not break a list unless there are some non-line-ending commas.
+        # This avoids getting different results with only non-essential commas,
+        # and fixes b1192.
+        my $seqno = $type_sequence_stack[$dd];
+        my $real_comma_count =
+          $seqno ? $self->[_rtype_count_by_seqno_]->{$seqno}->{','} : 1;
+
         # anything to do?
         if ( $item_count_stack[$dd] ) {
 
@@ -16038,7 +16045,7 @@ sub set_continuation_breaks {
             }
 
             # handle commas within containers...
-            else {
+            elsif ($real_comma_count) {
                 my $fbc = get_forced_breakpoint_count();
 
                 # always open comma lists not preceded by keywords,
@@ -16289,7 +16296,9 @@ sub set_continuation_breaks {
         my $i_line_start = -1;
         my $i_last_colon = -1;
 
-        # loop over all tokens in this batch
+        #########################################
+        # Main loop over all tokens in this batch
+        #########################################
         while ( ++$i <= $max_index_to_go ) {
             if ( $type ne 'b' ) {
                 $i_last_nonblank_token    = $i - 1;
diff --git a/local-docs/BugLog.pod b/local-docs/BugLog.pod
index 46aad0d3..989c0585 100644
--- a/local-docs/BugLog.pod
+++ b/local-docs/BugLog.pod
@@ -2,6 +2,28 @@
 
 =over 4
 
+=item B<Fix formatting instability, b1192>
+
+Testing with random parameters produced unstable formatting with the
+following snippet when run with some unusual parameters:
+
+          @EXPORT =
+              ( @{$EXPORT_TAGS{standard}}, );
+
+It was also be formatted as
+
+          @EXPORT = (
+                      @{$EXPORT_TAGS{standard}},
+          );
+
+The problem was that a list formatting style was turning on and off due to the
+the needless terminal comma within the parens.  A patch was made to ignore
+commas like this when deciding if list formatting should be used.
+
+This fixes case b1192.
+
+10 Aug 2021.
+
 =item B<Fix formatting instability, b1191>
 
 Random testing produced an instability involving an unusual parameter
-- 
2.39.5