casing: don’t assume letters are *either* upper- or lower-case (bug#24603)

A compatibility digraph characters, such as Dž, are neither upper- nor
lower-case.  At the moment however, those are reported as upper-case¹
despite the fact that they change when upper-cased.

Stop checking if a character is upper-case before trying to up-case it
so that title-case characters are handled correctly.  This fixes one of
the issues mentioned in bug#24603.

¹ Because they change when converted to lower-case.  Notice an asymmetry
  in that for a character to be considered lower-case it must not be
  upper-case (plus the usual condition of changing when upper-cased).

* src/buffer.h (upcase1): Delete.
(upcase): Change to upcase character unconditionally just like downcase
does it.  This is what upcase1 was.

* src/casefiddle.c (casify_object, casify_region): Use upcase instead
of upcase1 and don’t check !uppercasep(x) before calling upcase.

* src/keyboard.c (read_key_sequence): Don’t check if uppercase(x), just
downcase(x) and see if it changed.

* test/src/casefiddle-tests.el (casefiddle-tests--characters,
casefiddle-tests-casing): Update test cases which are now passing.

5 files changed, 42 insertions, 37 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 421e5daa3e4..a54c655c36d 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -338,6 +338,12 @@ same as in modes where the character is not whitespace.
 Instead of only checking the modification time, Emacs now also checks
 the file's actual content before prompting the user.
 
+** Title case characters are properly converted to upper case.
+'upcase', 'upcase-region' et al. convert title case characters (such
+as Dz) into their upper case form (such as DZ).  As a downside,
+'capitalize' and 'upcase-initials' produce awkward words where first
+two letters are upper case, e.g. DŽungla (instead of Džungla).
+
 
 * Changes in Specialized Modes and Packages in Emacs 26.1
 
@@ -1028,7 +1034,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
 
 
 Local variables:
-coding: us-ascii
+coding: utf-8
 mode: outline
 paragraph-separate: "[  ]*$"
 end:
diff --git a/src/buffer.h b/src/buffer.h
index 4a23e4fdd2e..f53212e3120 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -1365,28 +1365,28 @@ downcase (int c)
   return NATNUMP (down) ? XFASTINT (down) : c;
 }
 
-/* True if C is upper case.  */
-INLINE bool uppercasep (int c) { return downcase (c) != c; }
-
-/* Upcase a character C known to be not upper case.  */
+/* Upcase a character C, or make no change if that cannot be done. */
 INLINE int
-upcase1 (int c)
+upcase (int c)
 {
   Lisp_Object upcase_table = BVAR (current_buffer, upcase_table);
   Lisp_Object up = CHAR_TABLE_REF (upcase_table, c);
   return NATNUMP (up) ? XFASTINT (up) : c;
 }
 
+/* True if C is upper case.  */
+INLINE bool uppercasep (int c)
+{
+  return downcase (c) != c;
+}
+
 /* True if C is lower case.  */
 INLINE bool
 lowercasep (int c)
 {
-  return !uppercasep (c) && upcase1 (c) != c;
+  return !uppercasep (c) && upcase (c) != c;
 }
 
-/* Upcase a character C, or make no change if that cannot be done.  */
-INLINE int upcase (int c) { return uppercasep (c) ? c : upcase1 (c); }
-
 INLINE_HEADER_END
 
 #endif /* EMACS_BUFFER_H */
diff --git a/src/casefiddle.c b/src/casefiddle.c
index 28ffcb298ff..b2b87e7a858 100644
--- a/src/casefiddle.c
+++ b/src/casefiddle.c
@@ -64,13 +64,9 @@ casify_object (enum case_action flag, Lisp_Object obj)
         multibyte = 1;
       if (! multibyte)
         MAKE_CHAR_MULTIBYTE (c1);
-      c = downcase (c1);
-      if (inword)
-        XSETFASTINT (obj, c | flags);
-      else if (c == (XFASTINT (obj) & ~flagbits))
+      c = flag == CASE_DOWN ? downcase (c1) : upcase (c1);
+      if (c != c1)
         {
-          if (! inword)
-            c = upcase1 (c1);
           if (! multibyte)
             MAKE_CHAR_UNIBYTE (c);
           XSETFASTINT (obj, c | flags);
@@ -95,7 +91,7 @@ casify_object (enum case_action flag, Lisp_Object obj)
             c = downcase (c);
           else if (!uppercasep (c)
                    && (!inword || flag != CASE_CAPITALIZE_UP))
-            c = upcase1 (c1);
+            c = upcase (c1);
           if ((int) flag >= (int) CASE_CAPITALIZE)
             inword = (SYNTAX (c) == Sword);
           if (c != c1)
@@ -127,9 +123,8 @@ casify_object (enum case_action flag, Lisp_Object obj)
           c = STRING_CHAR_AND_LENGTH (SDATA (obj) + i_byte, len);
           if (inword && flag != CASE_CAPITALIZE_UP)
             c = downcase (c);
-          else if (!uppercasep (c)
-                   && (!inword || flag != CASE_CAPITALIZE_UP))
-            c = upcase1 (c);
+          else if (!inword || flag != CASE_CAPITALIZE_UP)
+            c = upcase (c);
           if ((int) flag >= (int) CASE_CAPITALIZE)
             inword = (SYNTAX (c) == Sword);
           o += CHAR_STRING (c, o);
@@ -236,9 +231,8 @@ casify_region (enum case_action flag, Lisp_Object b, Lisp_Object e)
       c2 = c;
       if (inword && flag != CASE_CAPITALIZE_UP)
         c = downcase (c);
-      else if (!uppercasep (c)
-               && (!inword || flag != CASE_CAPITALIZE_UP))
-        c = upcase1 (c);
+      else if (!inword || flag != CASE_CAPITALIZE_UP)
+        c = upcase (c);
       if ((int) flag >= (int) CASE_CAPITALIZE)
         inword = ((SYNTAX (c) == Sword)
                   && (inword || !syntax_prefix_flag_p (c)));
diff --git a/src/keyboard.c b/src/keyboard.c
index ed8e71fd0a7..0fad633581d 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -9642,22 +9642,26 @@ read_key_sequence (Lisp_Object *keybuf, int bufsize, Lisp_Object prompt,
          use the corresponding lower-case letter instead.  */
       if (NILP (current_binding)
           && /* indec.start >= t && fkey.start >= t && */ keytran.start >= t
-          && INTEGERP (key)
-          && ((CHARACTERP (make_number (XINT (key) & ~CHAR_MODIFIER_MASK))
-               && uppercasep (XINT (key) & ~CHAR_MODIFIER_MASK))
-              || (XINT (key) & shift_modifier)))
+          && INTEGERP (key))
         {
           Lisp_Object new_key;
+          int k = XINT (key);
+
+          if (k & shift_modifier)
+            XSETINT (new_key, k & ~shift_modifier);
+          else if (CHARACTERP (make_number (k & ~CHAR_MODIFIER_MASK)))
+            {
+              int dc = downcase(k & ~CHAR_MODIFIER_MASK);
+              if (dc == (k & ~CHAR_MODIFIER_MASK))
+                goto not_upcase;
+              XSETINT (new_key, dc | (k & CHAR_MODIFIER_MASK));
+            }
+          else
+            goto not_upcase;
 
           original_uppercase = key;
           original_uppercase_position = t - 1;
 
-          if (XINT (key) & shift_modifier)
-            XSETINT (new_key, XINT (key) & ~shift_modifier);
-          else
-            XSETINT (new_key, (downcase (XINT (key) & ~CHAR_MODIFIER_MASK)
-                               | (XINT (key) & CHAR_MODIFIER_MASK)));
-
           /* We have to do this unconditionally, regardless of whether
              the lower-case char is defined in the keymaps, because they
              might get translated through function-key-map.  */
@@ -9668,6 +9672,7 @@ read_key_sequence (Lisp_Object *keybuf, int bufsize, Lisp_Object prompt,
           goto replay_sequence;
         }
 
+    not_upcase:
       if (NILP (current_binding)
           && help_char_p (EVENT_HEAD (key)) && t > 1)
             {
diff --git a/test/src/casefiddle-tests.el b/test/src/casefiddle-tests.el
index c752bb09172..152d85de006 100644
--- a/test/src/casefiddle-tests.el
+++ b/test/src/casefiddle-tests.el
@@ -63,13 +63,13 @@
     (?Ł ?Ł ?ł ?Ł)
     (?ł ?Ł ?ł ?Ł)
 
-    ;; FIXME(bug#24603): We should have:
+    ;; FIXME(bug#24603): Commented ones are what we want.
     ;;(?DŽ ?DŽ ?dž ?Dž)
-    ;; but instead we have:
     (?DŽ ?DŽ ?dž ?DŽ)
-    ;; FIXME(bug#24603): Those two are broken at the moment:
     ;;(?Dž ?DŽ ?dž ?Dž)
+    (?Dž ?DŽ ?dž ?DŽ)
     ;;(?dž ?DŽ ?dž ?Dž)
+    (?dž ?DŽ ?dž ?DŽ)
 
     (?Σ ?Σ ?σ ?Σ)
     (?σ ?Σ ?σ ?Σ)
@@ -197,7 +197,7 @@
         ;;("ΌΣΟΣ" "ΌΣΟΣ" "όσος" "Όσος" "Όσος")
         ;; And here’s what is actually happening:
         ("DŽUNGLA" "DŽUNGLA" "džungla" "DŽungla" "DŽUNGLA")
-        ("Džungla" "��UNGLA" "džungla" "��ungla" "��ungla")
+        ("Džungla" "��UNGLA" "džungla" "��ungla" "��ungla")
         ("džungla" "DŽUNGLA" "džungla" "DŽungla" "DŽungla")
         ("define" "DEfiNE" "define" "Define" "Define")
         ("fish" "fiSH" "fish" "fish" "fish")