pv_uni_display: Use common fcn; \b mnemonic

This removes the (almost) duplicate code in this function to display
mnemonics for control characters that have them.  The reason the two
pieces of code aren't precisely the same is that the other function also
uses \b as a mnemonic for backspace.  Using all possible mnemonics is
desirable, so a flag is added for pv_uni_display to now use \b.  This is
now by default enabled in double-quoted strings, but not regex patterns
(as \b there means something quite different except in character classes).
B.pm is changed to expect \b.

1 files changed, 7 insertions, 1 deletions

diff --git a/utf8.h b/utf8.h
index fa036f0e05..fb835073b6 100644
--- a/utf8.h
+++ b/utf8.h
@@ -1009,7 +1009,13 @@ Evaluates to 0xFFFD, the code point of the Unicode REPLACEMENT CHARACTER
 
 #define UNI_DISPLAY_ISPRINT	0x0001
 #define UNI_DISPLAY_BACKSLASH	0x0002
-#define UNI_DISPLAY_QQ		(UNI_DISPLAY_ISPRINT|UNI_DISPLAY_BACKSLASH)
+#define UNI_DISPLAY_BACKSPACE	0x0004  /* Allow \b when also
+                                           UNI_DISPLAY_BACKSLASH */
+#define UNI_DISPLAY_QQ		(UNI_DISPLAY_ISPRINT                \
+                                |UNI_DISPLAY_BACKSLASH              \
+                                |UNI_DISPLAY_BACKSPACE)
+
+/* Character classes could also allow \b, but not patterns in general */
 #define UNI_DISPLAY_REGEX	(UNI_DISPLAY_ISPRINT|UNI_DISPLAY_BACKSLASH)
 
 #define ANYOF_FOLD_SHARP_S(node, input, end)	\