bug#24603: [RFC 11/18] Implement casing rules for Lithuanian

[Michal Nazarewicz]

In Lithuanian, tittle above lower case i and j are retained even if
there are other diacritics above present.  For that to work, an explicit
combining dot above must be added after i and j or otherwise the
rendering engine will remove the tittle.

* src/casefiddle.c (struct casing_context, prepare_casing_context): Add
lithuanian_tittle member to hold state of Lithuanian rules handling.
(case_lithuanian): New function which implements Lithuanian rules.
(case_characters): Make use of case_lithuanian.

* test/src/casefiddle-tests.el (casefiddle-tests-casing): Add test cases
for Lithuanian rules.
---
 src/casefiddle.c             | 149 +++++++++++++++++++++++++++++++++++++++++--
 test/src/casefiddle-tests.el |  27 +++++++-
 2 files changed, 170 insertions(+), 6 deletions(-)

diff --git a/src/casefiddle.c b/src/casefiddle.c
index 2a7aa64..0377fe6 100644
--- a/src/casefiddle.c
+++ b/src/casefiddle.c
@@ -56,6 +56,16 @@ struct casing_context {
   bool inword;
   /* Whether to apply Azeri/Turkish rules for dotted and dotless i. */
   bool treat_turkic_i;
+
+  /* Whether to use Lithuanian rules for i’s and j’s tittle. */
+  unsigned char lithuanian_tittle;
+#define LT_OFF 0  /* No */
+#define LT_ON 1  /* Yes */
+#define LT_DEL_DOT_ABOVE 2  /* Yes and look out for combining dot above to
+                              delete. */
+#define LT_INS_DOT_ABOVE 3  /* Yes and look out for diacritics combining above
+                              because we may need to inject dot above before
+                              them. */
 };
 
 /* Initialise CTX structure and prepares related global data for casing
@@ -64,7 +74,7 @@ static void
 prepare_casing_context (struct casing_context *ctx,
                        enum case_action flag, bool inbuffer)
 {
-  Lisp_Object lang, l, tr, az;
+  Lisp_Object lang, l, tr, az, lt;
 
   ctx->flag = flag;
   ctx->inbuffer = inbuffer;
@@ -74,6 +84,7 @@ prepare_casing_context (struct casing_context *ctx,
     : Qnil;
 
   ctx->treat_turkic_i = false;
+  ctx->lithuanian_tittle = LT_OFF;
 
   /* If the case table is flagged as modified, rescan it.  */
   if (NILP (XCHAR_TABLE (BVAR (current_buffer, downcase_table))->extras[1]))
@@ -86,6 +97,7 @@ prepare_casing_context (struct casing_context *ctx,
   lang = Vcurrent_iso639_language;
   tr = intern_c_string ("tr");
   az = intern_c_string ("az");
+  lt = intern_c_string ("lt");
   if (SYMBOLP (lang))
     {
       l = lang;
@@ -97,10 +109,9 @@ prepare_casing_context (struct casing_context *ctx,
       lang = XCDR (lang);
     check_language:
       if (EQ (l, tr) || EQ (l, az))
-       {
-         ctx->treat_turkic_i = true;
-         break;
-       }
+       ctx->treat_turkic_i = true;
+      else if (EQ (l, lt))
+       ctx->lithuanian_tittle = LT_ON;
     }
 }
 
@@ -199,6 +210,131 @@ case_character_impl (struct casing_str_buf *buf,
 #define CAPITAL_DOTTED_I    0x130
 #define SMALL_DOTLESS_I     0x131
 #define COMBINING_DOT_ABOVE 0x307
+
+/* Lithuanian retains tittle in lower case i and j when there are more
+   accents above those letters. */
+
+#define CAPITAL_I_WITH_GRAVE  0x0CC
+#define CAPITAL_I_WITH_ACUTE  0x0CD
+#define CAPITAL_I_WITH_TILDE  0x128
+#define CAPITAL_I_WITH_OGONEK 0x12E
+#define SMALL_I_WITH_OGONEK   0x12F
+#define COMBINING_GRAVE_ABOVE 0x300
+#define COMBINING_ACUTE_ABOVE 0x301
+#define COMBINING_TILDE_ABOVE 0x303
+#define COMBINING_OGONEK      0x328
+
+/* Attempt to case CH using rules for Lithuanian i and j.  Return true if
+   character has been cased (in which case it’s saved in BUF), false otherwise.
+   If CTX->lithuanian_tittle is LT_OFF, return false. */
+static bool
+case_lithuanian (struct casing_str_buf *buf, struct casing_context *ctx,
+                enum case_action flag, int ch)
+{
+  switch (__builtin_expect(ctx->lithuanian_tittle, LT_OFF)) {
+  case LT_OFF:
+    return false;
+
+  case LT_DEL_DOT_ABOVE:
+    /* When upper-casing i or j, a combining dot above that follows it must be
+       removed.  This is true even if there’s a combining ogonek in between.
+       But, if there’s another character combining above in between, combining
+       dot needs to stay (since the dot will be rendered above the other
+       diacritic). */
+    switch (ch) {
+    case COMBINING_DOT_ABOVE:
+      buf->len_chars = buf->len_bytes = 0;
+      ctx->lithuanian_tittle = LT_ON;
+      return true;
+    case COMBINING_GRAVE_ABOVE:
+    case COMBINING_ACUTE_ABOVE:
+    case COMBINING_TILDE_ABOVE:
+      ctx->lithuanian_tittle = LT_ON;
+      return false;
+    case COMBINING_OGONEK:
+      return false;
+    default:
+      ctx->lithuanian_tittle = LT_ON;
+    }
+    break;
+
+  case LT_INS_DOT_ABOVE:
+    /* When lower-casing I or J, if the letter has any accents above,
+       a combining dot above must be added before them.  If we are here, it
+       means that we have lower cased I or J and we’re now on the lookout for
+       accents combining above. */
+    switch (ch) {
+    case COMBINING_GRAVE_ABOVE:
+    case COMBINING_ACUTE_ABOVE:
+    case COMBINING_TILDE_ABOVE:
+      buf->len_chars = 2;
+      buf->len_bytes = CHAR_STRING (COMBINING_DOT_ABOVE, buf->data);
+      buf->len_bytes += CHAR_STRING (ch, buf->data + buf->len_bytes);
+      ctx->lithuanian_tittle = LT_ON;
+      return true;
+    case COMBINING_OGONEK:
+      return false;
+    default:
+      ctx->lithuanian_tittle = LT_ON;
+    }
+    break;
+  }
+
+  switch (flag) {
+  case CASE_UP:
+  case CASE_CAPITALIZE:
+    if (ch == 'i' || ch == 'j')
+      {
+       buf->data[0] = ch ^ ('i' ^ 'I');
+       buf->len_bytes = 1;
+      }
+    else if (ch == SMALL_I_WITH_OGONEK)
+      buf->len_bytes = CHAR_STRING (CAPITAL_I_WITH_OGONEK, buf->data);
+    else
+      break;
+    buf->len_chars = 1;
+    /* Change the state so we’re on the lookout for combining dot above. */
+    ctx->lithuanian_tittle = LT_DEL_DOT_ABOVE;
+    return true;
+
+  case CASE_DOWN:
+    /* Turning I or J to lower case requires combining dot above to be included
+       IF there are any other characters combining above present.  This is so
+       that the tittle is preserved. */
+    switch (ch) {
+    case CAPITAL_I_WITH_GRAVE:
+      ch = 0x80;  /* U+300, "\xCC\x80", combining grave accent */
+      goto has_accent;
+    case CAPITAL_I_WITH_ACUTE:
+      ch = 0x81;  /* U+301, "\xCC \x81", combining acute accent */
+      goto has_accent;
+    case CAPITAL_I_WITH_TILDE:
+      ch = 0x83;  /* U+303, "\xCC\x83", combining tilde */
+    has_accent:
+      memcpy (buf->data, "i\xCC\x87\xCC", 4);
+      buf->data[4] = ch;
+      buf->len_chars = 3;
+      buf->len_bytes = 5;
+      return true;
+
+    case 'I':
+    case 'J':
+      buf->data[0] = ch ^ ('i' ^ 'I');
+      buf->len_bytes = 1;
+      if (false)
+    case CAPITAL_I_WITH_OGONEK:
+       buf->len_bytes = CHAR_STRING (SMALL_I_WITH_OGONEK, buf->data);
+      buf->len_chars = 1;
+      /* Change the state so we’re on the lookout for diacritics combining
+        above.  If one is found, we need to add combining dot above. */
+      ctx->lithuanian_tittle = LT_INS_DOT_ABOVE;
+      return true;
+    }
+    break;
+  }
+
+  return false;
+}
 
 /* Based on CTX, case character CH accordingly.  Update CTX as necessary.
    Return cased character.
@@ -234,6 +370,9 @@ case_characters (struct casing_str_buf *buf, struct 
casing_context *ctx,
 {
   enum case_action flag = normalise_flag (ctx);
 
+  if (case_lithuanian (buf, ctx, flag, ch))
+    return 0;
+
   if (flag != CASE_NO_ACTION && __builtin_expect(ctx->treat_turkic_i, false))
     {
       bool dot_above = false;
diff --git a/test/src/casefiddle-tests.el b/test/src/casefiddle-tests.el
index 9f5e43f..bae4242 100644
--- a/test/src/casefiddle-tests.el
+++ b/test/src/casefiddle-tests.el
@@ -185,7 +185,32 @@ casefiddle-tests--characters
               ("I\u0307si\u0307s" "I\u0307Sİ\u0307S" "isi\u0307s"
                                   "I\u0307si\u0307s" "I\u0307si\u0307s" 'tr)
               ("I\u0307sI\u0307s" "I\u0307SI\u0307S" "isis"
-                                  "I\u0307sis" "I\u0307sI\u0307s" 'tr))
+                                  "I\u0307sis" "I\u0307sI\u0307s" 'tr)
+
+              ;; Test combining dot above in inserted when needed when lower
+              ;; casing I or J.
+              ("I\u0328\u0300"          ; I + ogonek + grave
+               "I\u0328\u0300" "i\u0328\u0307\u0300"
+               "I\u0328\u0300" "I\u0328\u0300" 'lt)
+
+              ("J\u0328\u0300"          ; J + ogonek + grave
+               "J\u0328\u0300" "j\u0328\u0307\u0300"
+               "J\u0328\u0300" "J\u0328\u0300" 'lt)
+
+              ("Į\u0300"          ; I-ogonek + grave
+               "Į\u0300" "į\u0307\u0300" "Į\u0300" "Į\u0300" 'lt)
+
+              ("Ì Í Ĩ"
+               "Ì Í Ĩ" "i\u0307\u0300 i\u0307\u0301 i\u0307\u0303"
+               "Ì Í Ĩ" "Ì Í Ĩ" 'lt)
+
+              ;; Test combining dot above in removed when upper casing i or j.
+              ("i\u0328\u0307"          ; i + ogonek + dot above
+               "I\u0328" "i\u0328\u0307" "I\u0328" "I\u0328" 'lt)
+              ("j\u0328\u0307"          ; j + ogonek + dot above
+               "J\u0328" "j\u0328\u0307" "J\u0328" "J\u0328" 'lt)
+              ("į\u0307"                ; i-ogonek + dot above
+               "Į" "į\u0307" "Į" "Į" 'lt))
             (nreverse errors))
          (let* ((input (string-to-multibyte (car test)))
                 (expected (cdr test))
-- 
2.8.0.rc3.226.g39d4020