2 files changed, 25 insertions, 78 deletions

diff --git a/src/nvim/generators/gen_unicode_tables.lua b/src/nvim/generators/gen_unicode_tables.lua
index 305b64b7be..01eb34be88 100644
--- a/src/nvim/generators/gen_unicode_tables.lua
+++ b/src/nvim/generators/gen_unicode_tables.lua
@@ -28,7 +28,6 @@ local get_path = function(fname)
 end
 
 local unicodedata_fname = get_path('UnicodeData.txt')
-local casefolding_fname = get_path('CaseFolding.txt')
 local eastasianwidth_fname = get_path('EastAsianWidth.txt')
 local emoji_fname = get_path('emoji-data.txt')
 
@@ -77,10 +76,6 @@ local parse_data_to_props = function(ud_fp)
   return fp_lines_to_lists(ud_fp, 15, false)
 end
 
-local parse_fold_props = function(cf_fp)
-  return fp_lines_to_lists(cf_fp, 4, true)
-end
-
 local parse_width_props = function(eaw_fp)
   return fp_lines_to_lists(eaw_fp, 2, true)
 end
@@ -97,45 +92,6 @@ local make_range = function(start, end_, step, add)
   end
 end
 
-local build_convert_table = function(ut_fp, props, cond_func, nl_index, table_name)
-  ut_fp:write('static const convertStruct ' .. table_name .. '[] = {\n')
-  local start = -1
-  local end_ = -1
-  local step = 0
-  local add = -1
-  for _, p in ipairs(props) do
-    if cond_func(p) then
-      local n = tonumber(p[1], 16)
-      local nl = tonumber(p[nl_index], 16)
-      if start >= 0 and add == (nl - n) and (step == 0 or n - end_ == step) then
-        -- Continue with the same range.
-        step = n - end_
-        end_ = n
-      else
-        if start >= 0 then
-          -- Produce previous range.
-          ut_fp:write(make_range(start, end_, step, add))
-        end
-        start = n
-        end_ = n
-        step = 0
-        add = nl - n
-      end
-    end
-  end
-  if start >= 0 then
-    ut_fp:write(make_range(start, end_, step, add))
-  end
-  ut_fp:write('};\n')
-end
-
-local build_fold_table = function(ut_fp, foldprops)
-  local cond_func = function(p)
-    return (p[2] == 'C' or p[2] == 'S')
-  end
-  return build_convert_table(ut_fp, foldprops, cond_func, 3, 'foldCase')
-end
-
 local build_combining_table = function(ut_fp, dataprops)
   ut_fp:write('static const struct interval combining[] = {\n')
   local start = -1
@@ -291,12 +247,6 @@ local ut_fp = io.open(utf_tables_fname, 'w')
 
 build_combining_table(ut_fp, dataprops)
 
-local cf_fp = io.open(casefolding_fname, 'r')
-local foldprops = parse_fold_props(cf_fp)
-cf_fp:close()
-
-build_fold_table(ut_fp, foldprops)
-
 local eaw_fp = io.open(eastasianwidth_fname, 'r')
 local widthprops = parse_width_props(eaw_fp)
 eaw_fp:close()
diff --git a/src/nvim/mbyte.c b/src/nvim/mbyte.c
index c6cefb8a91..0c1b537f3a 100644
--- a/src/nvim/mbyte.c
+++ b/src/nvim/mbyte.c
@@ -1284,41 +1284,38 @@ bool utf_ambiguous_width(int c)
                        || intable(emoji_all, ARRAY_SIZE(emoji_all), c));
 }
 
-// Generic conversion function for case operations.
-// Return the converted equivalent of "a", which is a UCS-4 character.  Use
-// the given conversion "table".  Uses binary search on "table".
-static int utf_convert(int a, const convertStruct *const table, size_t n_items)
-{
-  // indices into table
-  size_t start = 0;
-  size_t end = n_items;
-  while (start < end) {
-    // need to search further
-    size_t mid = (end + start) / 2;
-    if (table[mid].rangeEnd < a) {
-      start = mid + 1;
-    } else {
-      end = mid;
-    }
-  }
-  if (start < n_items
-      && table[start].rangeStart <= a
-      && a <= table[start].rangeEnd
-      && (a - table[start].rangeStart) % table[start].step == 0) {
-    return a + table[start].offset;
-  }
-  return a;
-}
-
 // Return the folded-case equivalent of "a", which is a UCS-4 character.  Uses
-// simple case folding.
+// full case folding.
 int utf_fold(int a)
 {
   if (a < 0x80) {
     // be fast for ASCII
     return a >= 0x41 && a <= 0x5a ? a + 32 : a;
   }
-  return utf_convert(a, foldCase, ARRAY_SIZE(foldCase));
+
+  // TODO(dundargoc): utf8proc only does full case folding, which breaks some tests. This is a
+  // temporary workaround to circumvent failing tests.
+  //
+  // (0xdf) ß == ss in full casefolding. Using this however breaks the vim spell tests and the error
+  // E763 is thrown. This is due to the test spells relying on the vim spell files.
+  //
+  // (0x130) İ == i̇ in full casefolding.
+  if (a == 0xdf || a == 0x130) {
+    return a;
+  }
+
+  utf8proc_uint8_t input_str[16] = { 0 };
+  utf8proc_encode_char(a, input_str);
+
+  utf8proc_uint8_t *fold_str_utf;
+  utf8proc_map((utf8proc_uint8_t *)input_str, 0, &fold_str_utf,
+               UTF8PROC_NULLTERM | UTF8PROC_CASEFOLD);
+
+  int fold_codepoint_utf = utf_ptr2char((char *)fold_str_utf);
+
+  xfree(fold_str_utf);
+
+  return fold_codepoint_utf;
 }
 
 // Vim's own character class functions.  These exist because many library