fix handling of 'seen' flag wrt placeholders

while we don't want to propagate seeing _from_ the placeholder, we do
want to propagate it _to_ it, and consequently also un-seeing from it.

src/run-tests.pl

@@ -1113,35 +1113,49 @@ test("noop + expunge near side", \@x01, \@X0A, \@O0A);
 my @x20 = (
   0, 0, 0,
   A, "*", "", "",
-  B, "*FP*", "", "",
+  B, "*FPS*", "", "",
-  C, "", "", "*F*",
+  C, "", "", "*FS*",
 );
 
 my @O21 = ("MaxSize 1k\n", "MaxSize 1k\n", "Expunge Near");
 my @X21 = (
   C, 0, B,
-  C, "*?", "*<", "",
+  C, "*S?", "*<S", "",
   A, "", "*", "*",
-  B, "", "*>P", "*P?",
+  B, "", "*>PS", "*PS?",
 );
 test("max size", \@x20, \@X21, \@O21);
 
 my @x22 = (
-  E, 0, V,
+  L, 0, V,
   A, "*", "", "",
   B, "*PR*", "", "",
   V, "*FPR*", "", "",
   C, "*FPR?", "*<DP", "*DP*",
   W, "*FPR?", "*<DP", "*DFP*",
+  M, "*FS?", "*<", "**",
+  N, "*FS?", "*<S", "**",
+  O, "*FS?", "*<S", "*S*",
+  P, "*FS?", "*<", "*S*",
+  Q, "*F?", "*<S", "*S*",
+  R, "*F?", "*<", "*S*",
+  S, "*F?", "*<S", "**",
   D, "*PR?", "*<DP", "*DFP*",
   E, "*PR*", "*>DP", "*DP?",
+  F, "*S*", "*>", "*?",
+  G, "*S*", "*>S", "*?",
+  H, "*S*", "*>S", "*S?",
+  I, "*S*", "*>", "*S?",
+  J, "**", "*>S", "*S?",
+  K, "**", "*>", "*S?",
+  L, "**", "*>S", "*?",
   A, "", "*", "*",
   B, "", "*>DP", "*DFP?",
   V, "", "*>DP", "*DFP?",
 );
 
 my @X22 = (
-  W, 0, V,
+  S, 0, V,
   B, "", ">->D+R", "^PR*",
   B, "", "", "&1/",
   V, "", ">->D+FR", "^FPR*",
@@ -1150,8 +1164,27 @@ my @X22 = (
   C, "&1+T", "^", "&",
   W, "^FPR*", "<-<D+FR", "-D+R",
   W, "&1+T", "^", "&",
+  M, "^*", "<-<", "",
+  M, "&1+T", "^", "&",
+  N, "^*", "<-<S", "",
+  N, "&1+T", "^", "&",
+  O, "^S*", "<-<", "",
+  O, "&1+T", "^", "&",
+  P, "^S*", "<-<+S", "",
+  P, "&1+T", "^", "&",
+  Q, "^*", "<-<S", "-S",
+  Q, "&1+T", "^", "&",
+  R, "^S*", "<-<+S", "",
+  R, "&1+T", "^", "&",
+  S, "^*", "<-<S", "",
+  S, "&1+T", "^", "&",
   D, "", "-D+R", "-D+R",
   E, "", "-D+R", "-D+R",
+  F, "", "+S", "+S",
+  G, "-S", "-S", "",
+  I, "", "+S", "",
+  J, "", "-S", "-S",
+  L, "", "-S", "",
 );
 test("max size + flagging", \@x22, \@X22, \@O21);
 
@@ -1308,8 +1341,8 @@ test("maxuid topping", \@x60, \@X61, \@O61);
 
 my @x90 = (
   C, 0, C,
-  A, "*DRT*", "*>D", "*DFP?",
+  A, "*DRT*", "*>DS", "*DFPS?",
-  B, "*DR*", "*>D", "*DFPT?",
+  B, "*DR*", "*>DS", "*DFPST?",
   C, "*", "*", "*",
   D, "*T", "", "",
 );

src/sync.c

@@ -1054,7 +1054,7 @@ box_loaded( int sts, message_t *msgs, int total_msgs, int recent_msgs, void *aux
 				if ((svars->chan->ops[t] & OP_RENEW) && (srec->status & S_DUMMY(t)) && srec->uid[t^1] && srec->msg[t]) {
 					sflags = srec->msg[t]->flags;
 					if (sflags & F_FLAGGED) {
-						sflags &= ~(F_SEEN | F_FLAGGED);  // As below.
+						sflags &= ~(F_SEEN | F_FLAGGED) | (srec->flags & F_SEEN);  // As below.
 						// We save away the dummy's flags, because after an
 						// interruption it may be already gone.
 						srec->pflags = sflags;
@@ -1136,9 +1136,10 @@ box_loaded( int sts, message_t *msgs, int total_msgs, int recent_msgs, void *aux
 						}
 						if (srec->status & S_DUMMY(t^1)) {
 							// From placeholders, don't propagate:
-							// - Seen, because the real contents were obviously not seen yet
+							// - Seen, because the real contents were obviously not seen yet.
+							//   However, we do propagate un-seeing.
 							// - Flagged, because it's just a request to upgrade
-							sflags &= ~(F_SEEN|F_FLAGGED);
+							sflags &= ~(F_SEEN | F_FLAGGED) | (srec->flags & F_SEEN);
 						} else if (srec->status & S_DUMMY(t)) {
 							// Don't propagate Flagged to placeholders, as that would be
 							// misunderstood as a request to upgrade next time around. We