1 files changed, 35 insertions, 16 deletions

diff --git a/src/nvim/spell.c b/src/nvim/spell.c
index d1428b0117..10cc410e81 100644
--- a/src/nvim/spell.c
+++ b/src/nvim/spell.c
@@ -441,7 +441,8 @@ size_t spell_check(
     MB_PTR_ADV(mi.mi_fend);
   }
 
-  (void)spell_casefold(ptr, (int)(mi.mi_fend - ptr), mi.mi_fword, MAXWLEN + 1);
+  (void)spell_casefold(wp, ptr, (int)(mi.mi_fend - ptr), mi.mi_fword,
+                       MAXWLEN + 1);
   mi.mi_fwordlen = (int)STRLEN(mi.mi_fword);
 
   if (camel_case) {
@@ -869,10 +870,11 @@ static void find_word(matchinf_T *mip, int mode)
 
           if (slang->sl_compsylmax < MAXWLEN) {
             // "fword" is only needed for checking syllables.
-            if (ptr == mip->mi_word)
-              (void)spell_casefold(ptr, wlen, fword, MAXWLEN);
-            else
+            if (ptr == mip->mi_word) {
+              (void)spell_casefold(mip->mi_win, ptr, wlen, fword, MAXWLEN);
+            } else {
               STRLCPY(fword, ptr, endlen[endidxcnt] + 1);
+            }
           }
           if (!can_compound(slang, fword, mip->mi_compflags))
             continue;
@@ -1315,9 +1317,9 @@ static int fold_more(matchinf_T *mip)
     MB_PTR_ADV(mip->mi_fend);
   }
 
-  (void)spell_casefold(p, (int)(mip->mi_fend - p),
-      mip->mi_fword + mip->mi_fwordlen,
-      MAXWLEN - mip->mi_fwordlen);
+  (void)spell_casefold(mip->mi_win, p, (int)(mip->mi_fend - p),
+                       mip->mi_fword + mip->mi_fwordlen,
+                       MAXWLEN - mip->mi_fwordlen);
   flen = (int)STRLEN(mip->mi_fword + mip->mi_fwordlen);
   mip->mi_fwordlen += flen;
   return flen;
@@ -2655,7 +2657,9 @@ static bool spell_iswordp_w(const int *p, const win_T *wp)
 // Uses the character definitions from the .spl file.
 // When using a multi-byte 'encoding' the length may change!
 // Returns FAIL when something wrong.
-int spell_casefold(char_u *str, int len, char_u *buf, int buflen)
+int spell_casefold(const win_T *wp, char_u *str, int len, char_u *buf,
+                   int buflen)
+  FUNC_ATTR_NONNULL_ALL
 {
   if (len >= buflen) {
     buf[0] = NUL;
@@ -2670,8 +2674,22 @@ int spell_casefold(char_u *str, int len, char_u *buf, int buflen)
       buf[outi] = NUL;
       return FAIL;
     }
-    const int c = mb_cptr2char_adv((const char_u **)&p);
-    outi += utf_char2bytes(SPELL_TOFOLD(c), buf + outi);
+    int c = mb_cptr2char_adv((const char_u **)&p);
+
+    // Exception: greek capital sigma 0x03A3 folds to 0x03C3, except
+    // when it is the last character in a word, then it folds to
+    // 0x03C2.
+    if (c == 0x03a3 || c == 0x03c2) {
+      if (p == str + len || !spell_iswordp(p, wp)) {
+        c = 0x03c2;
+      } else {
+        c = 0x03c3;
+      }
+    } else {
+      c = SPELL_TOFOLD(c);
+    }
+
+    outi += utf_char2bytes(c, buf + outi);
   }
   buf[outi] = NUL;
 
@@ -3155,7 +3173,8 @@ spell_find_suggest (
   if (su->su_badlen >= MAXWLEN)
     su->su_badlen = MAXWLEN - 1;        // just in case
   STRLCPY(su->su_badword, su->su_badptr, su->su_badlen + 1);
-  (void)spell_casefold(su->su_badptr, su->su_badlen, su->su_fbadword, MAXWLEN);
+  (void)spell_casefold(curwin, su->su_badptr, su->su_badlen, su->su_fbadword,
+                       MAXWLEN);
 
   // TODO(vim): make this work if the case-folded text is longer than the
   // original text. Currently an illegal byte causes wrong pointer
@@ -3535,7 +3554,7 @@ static void suggest_try_change(suginfo_T *su)
   STRCPY(fword, su->su_fbadword);
   n = (int)STRLEN(fword);
   p = su->su_badptr + su->su_badlen;
-  (void)spell_casefold(p, (int)STRLEN(p), fword + n, MAXWLEN - n);
+  (void)spell_casefold(curwin, p, (int)STRLEN(p), fword + n, MAXWLEN - n);
 
   for (int lpi = 0; lpi < curwin->w_s->b_langp.ga_len; ++lpi) {
     lp = LANGP_ENTRY(curwin->w_s->b_langp, lpi);
@@ -5087,7 +5106,7 @@ stp_sal_score (
     pbad = badsound;
   else {
     // soundfold the bad word with more characters following
-    (void)spell_casefold(su->su_badptr, stp->st_orglen, fword, MAXWLEN);
+    (void)spell_casefold(curwin, su->su_badptr, stp->st_orglen, fword, MAXWLEN);
 
     // When joining two words the sound often changes a lot.  E.g., "t he"
     // sounds like "t h" while "the" sounds like "@".  Avoid that by
@@ -5800,10 +5819,10 @@ void spell_soundfold(slang_T *slang, char_u *inword, bool folded, char_u *res)
     spell_soundfold_sofo(slang, inword, res);
   else {
     // SAL items used.  Requires the word to be case-folded.
-    if (folded)
+    if (folded) {
       word = inword;
-    else {
-      (void)spell_casefold(inword, (int)STRLEN(inword), fword, MAXWLEN);
+    } else {
+      (void)spell_casefold(curwin, inword, (int)STRLEN(inword), fword, MAXWLEN);
       word = fword;
     }