PATCH: [perl #134059] panic outputting a warning

This was due to a logic error on my part.  We need to save and restore a
value.  Instead, it was getting restored to the wrong value.

This particular instance of the bug was outputting a fatal error
message, so that the only harm is not giving the user the correct info,
and creating unnecessary work for them and us when it gets reported.
But this bug could manifest itself when trying to output just a warning
that the program otherwise would carry on from.

Author: khwilliamson

regcomp.c

@@ -131,6 +131,8 @@ struct RExC_state_t {
     char	*parse;			/* Input-scan pointer. */
     char        *copy_start;            /* start of copy of input within
                                            constructed parse string */
+    char        *save_copy_start;       /* Provides one level of saving
+                                           and restoring 'copy_start' */
     char        *copy_start_in_input;   /* Position in input string
                                            corresponding to copy_start */
     SSize_t	whilem_seen;		/* number of WHILEM in this expr */
@@ -229,6 +231,7 @@ struct RExC_state_t {
 #define RExC_precomp	(pRExC_state->precomp)
 #define RExC_copy_start_in_input (pRExC_state->copy_start_in_input)
 #define RExC_copy_start_in_constructed  (pRExC_state->copy_start)
+#define RExC_save_copy_start_in_constructed  (pRExC_state->save_copy_start)
 #define RExC_precomp_end (pRExC_state->precomp_end)
 #define RExC_rx_sv	(pRExC_state->rx_sv)
 #define RExC_rx		(pRExC_state->rx)
@@ -821,8 +824,13 @@ static const scan_data_t zero_scan_data = {
 } STMT_END
 
 /* Setting this to NULL is a signal to not output warnings */
-#define TURN_OFF_WARNINGS_IN_SUBSTITUTE_PARSE RExC_copy_start_in_constructed = NULL
-#define RESTORE_WARNINGS RExC_copy_start_in_constructed = RExC_precomp
+#define TURN_OFF_WARNINGS_IN_SUBSTITUTE_PARSE                               \
+    STMT_START {                                                            \
+      RExC_save_copy_start_in_constructed  = RExC_copy_start_in_constructed;\
+      RExC_copy_start_in_constructed = NULL;                                \
+    } STMT_END
+#define RESTORE_WARNINGS                                                    \
+    RExC_copy_start_in_constructed = RExC_save_copy_start_in_constructed
 
 /* Since a warning can be generated multiple times as the input is reparsed, we
  * output it the first time we come to that point in the parse, but suppress it

t/re/reg_mesg.t

@@ -318,6 +318,7 @@ my @death =
  '/\p{Is_Other_Alphabetic=F}/ ' => 'Can\'t find Unicode property definition "Is_Other_Alphabetic=F" {#} m/\p{Is_Other_Alphabetic=F}{#}/',
  '/\x{100}(?(/' => 'Unknown switch condition (?(...)) {#} m/\\x{100}(?({#}/', # [perl #133896]
  '/(?[\N{KEYCAP DIGIT NINE}/' => '\N{} in inverted character class or as a range end-point is restricted to one character {#} m/(?[\\N{U+39.FE0F.20E3{#}}/', # [perl #133988]
+ '/0000000000000000[\N{U+0.00}0000/' => 'Unmatched [ {#} m/0000000000000000[{#}\N{U+0.00}0000/', # [perl #134059]
 );
 
 # These are messages that are death under 'use re "strict"', and may or may