Make [:print:] support non-ASCII characters correctly

* src/regex.c (ISPRINT): Call 'printablep' for multibyte characters.
(BIT_PRINT): New bit mask.
(re_wctype_to_bit): Return BIT_PRINT for RECC_PRINT.
* src/character.c (printablep): New function.
* src/character.h (printablep): Add prototype.

* lisp/emacs-lisp/rx.el (rx): Doc fix: document the new behavior
of 'print', 'alnum', and 'alphabetic'.

* doc/lispref/searching.texi (Char Classes): Document the new
behavior of [:print:].

* etc/NEWS: Mention the new behavior of [:print:].

3 files changed, 23 insertions, 3 deletions

diff --git a/src/character.c b/src/character.c
index ad78f512f43..b357dd5a334 100644
--- a/src/character.c
+++ b/src/character.c
@@ -1022,6 +1022,22 @@ decimalnump (int c)
   return gen_cat == UNICODE_CATEGORY_Nd;
 }
 
+/* Return 'true' if C is a printable character as defined by its
+   Unicode properties.  */
+bool
+printablep (int c)
+{
+  Lisp_Object category = CHAR_TABLE_REF (Vunicode_category_table, c);
+  if (! INTEGERP (category))
+    return false;
+  EMACS_INT gen_cat = XINT (category);
+
+  /* See UTS #18.  */
+  return (!(gen_cat == UNICODE_CATEGORY_Cc /* control */
+            || gen_cat == UNICODE_CATEGORY_Cs /* surrogate */
+            || gen_cat == UNICODE_CATEGORY_Cn)); /* unassigned */
+}
+
 void
 syms_of_character (void)
 {
diff --git a/src/character.h b/src/character.h
index 7d902952db6..1a5d2c8a670 100644
--- a/src/character.h
+++ b/src/character.h
@@ -662,6 +662,7 @@ extern Lisp_Object string_escape_byte8 (Lisp_Object);
 
 extern bool alphabeticp (int);
 extern bool decimalnump (int);
+extern bool printablep (int);
 
 /* Return a translation table of id number ID.  */
 #define GET_TRANSLATION_TABLE(id) \
diff --git a/src/regex.c b/src/regex.c
index 1afc5037594..b9d09d02c22 100644
--- a/src/regex.c
+++ b/src/regex.c
@@ -318,7 +318,7 @@ enum syntaxcode { Swhitespace = 0, Sword = 1, Ssymbol = 2 };
 
 # define ISPRINT(c) (SINGLE_BYTE_CHAR_P (c)                             \
                     ? (c) >= ' ' && !((c) >= 0177 && (c) <= 0237)       \
-                    : 1)
+                     : printablep (c))
 
 # define ISALNUM(c) (IS_REAL_ASCII (c)                  \
                     ? (((c) >= 'a' && (c) <= 'z')       \
@@ -1865,7 +1865,8 @@ struct range_table_work_area
 #define RANGE_TABLE_WORK_ELT(work_area, i) ((work_area).table[i])
 
 /* Bits used to implement the multibyte-part of the various character classes
-   such as [:alnum:] in a charset's range table.  */
+   such as [:alnum:] in a charset's range table.  The code currently assumes
+   that only the low 16 bits are used.  */
 #define BIT_WORD        0x1
 #define BIT_LOWER       0x2
 #define BIT_PUNCT       0x4
@@ -1874,6 +1875,7 @@ struct range_table_work_area
 #define BIT_MULTIBYTE   0x20
 #define BIT_ALPHA       0x40
 #define BIT_ALNUM       0x80
+#define BIT_PRINT       0x100
 
 
 /* Set the bit for character C in a list.  */
@@ -2072,7 +2074,7 @@ re_wctype_to_bit (re_wctype_t cc)
 {
   switch (cc)
     {
-    case RECC_NONASCII: case RECC_PRINT: case RECC_GRAPH:
+    case RECC_NONASCII: case RECC_GRAPH:
     case RECC_MULTIBYTE: return BIT_MULTIBYTE;
     case RECC_ALPHA: return BIT_ALPHA;
     case RECC_ALNUM: return BIT_ALNUM;
@@ -2081,6 +2083,7 @@ re_wctype_to_bit (re_wctype_t cc)
     case RECC_UPPER: return BIT_UPPER;
     case RECC_PUNCT: return BIT_PUNCT;
     case RECC_SPACE: return BIT_SPACE;
+    case RECC_PRINT: return BIT_PRINT;
     case RECC_ASCII: case RECC_DIGIT: case RECC_XDIGIT: case RECC_CNTRL:
     case RECC_BLANK: case RECC_UNIBYTE: case RECC_ERROR: return 0;
     default: