vim-patch:9.1.0101: upper-case of German sharp s should be U+1E9E (#27449)

Problem:  upper-case of ß should be U+1E9E (CAPITAL LETTER SHARP S)
          (fenuks)
Solution: Make gU, ~ and g~ convert the U+00DF LATIN SMALL LETTER SHARP S (ß)
          to U+1E9E LATIN CAPITAL LETTER SHARP S (ẞ), update tests
          (glepnir)

This is part of Unicode 5.1.0 from April 2008, so should be fairly safe
to use now and since 2017 is part of the German standard orthography,
according to Wikipedia:
https://en.wikipedia.org/wiki/Capital_%E1%BA%9E#cite_note-auto-12

There is however one exception: UnicodeData.txt for U+00DF
LATIN SMALL LETTER SHARP S does NOT define U+1E9E LATIN CAPITAL LETTER
SHARP S as its upper case version. Therefore, toupper() won't be able
to convert from lower sharp s to upper case sharp s (the other way
around however works, since U+00DF is considered the lower case
character of U+1E9E and therefore tolower() works correctly for the
upper case version).

fixes: vim/vim#5573
closes: vim/vim#14018

https://github.com/vim/vim/commit/bd1232a1faf56b614a1e74c4ce51bc6e0650ae00

Co-authored-by: glepnir <glephunter@gmail.com>

6 files changed, 61 insertions, 21 deletions

diff --git a/src/nvim/mbyte.c b/src/nvim/mbyte.c
index fd353d8a67..f8451e62e2 100644
--- a/src/nvim/mbyte.c
+++ b/src/nvim/mbyte.c
@@ -1323,6 +1323,9 @@ int utf_fold(int a)
 // invalid values or can't handle latin1 when the locale is C.
 // Speed is most important here.
 
+// Note: UnicodeData.txt does not define U+1E9E as being the corresponding upper
+// case letter for U+00DF (ß), however it is part of the toLower table
+
 /// Return the upper-case equivalent of "a", which is a UCS-4 character.  Use
 /// simple case folding.
 int mb_toupper(int a)
diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index d785be54e5..f91df49e4f 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -2165,16 +2165,16 @@ bool swapchar(int op_type, pos_T *pos)
     return false;
   }
 
-  if (op_type == OP_UPPER && c == 0xdf) {
+  // ~ is OP_NOP, g~ is OP_TILDE, gU is OP_UPPER
+  if ((op_type == OP_UPPER || op_type == OP_NOP || op_type == OP_TILDE) && c == 0xdf) {
     pos_T sp = curwin->w_cursor;
 
-    // Special handling of German sharp s: change to "SS".
+    // Special handling for lowercase German sharp s (ß): convert to uppercase (ẞ).
     curwin->w_cursor = *pos;
     del_char(false);
-    ins_char('S');
-    ins_char('S');
+    ins_char(0x1E9E);
     curwin->w_cursor = sp;
-    inc(pos);
+    return true;
   }
 
   int nc = c;
diff --git a/test/functional/legacy/039_visual_block_mode_commands_spec.lua b/test/functional/legacy/039_visual_block_mode_commands_spec.lua
index 626035d74c..bc3fea765c 100644
--- a/test/functional/legacy/039_visual_block_mode_commands_spec.lua
+++ b/test/functional/legacy/039_visual_block_mode_commands_spec.lua
@@ -134,7 +134,7 @@ describe('Visual block mode', function()
   end)
 
   it('should make a selected part uppercase', function()
-    -- GUe must uppercase a whole word, also when ß changes to SS.
+    -- GUe must uppercase a whole word, also when ß changes to ẞ.
     feed('Gothe youtußeuu end<ESC>Ypk0wgUe<CR>')
     -- GUfx must uppercase until x, inclusive.
     feed('O- youßtußexu -<ESC>0fogUfx<CR>')
@@ -150,13 +150,13 @@ describe('Visual block mode', function()
 
     expect([[
       
-      the YOUTUSSEUU end
-      - yOUSSTUSSEXu -
-      THE YOUTUSSEUU END
-      111THE YOUTUSSEUU END
+      the YOUTUẞEUU end
+      - yOUẞTUẞEXu -
+      THE YOUTUẞEUU END
+      111THE YOUTUẞEUU END
       BLAH DI
       DOH DUT
-      222the yoUTUSSEUU END
+      222the yoUTUẞEUU END
       333THE YOUTUßeuu end]])
   end)
 
diff --git a/test/old/testdir/test_normal.vim b/test/old/testdir/test_normal.vim
index b98547061e..91c058df9e 100644
--- a/test/old/testdir/test_normal.vim
+++ b/test/old/testdir/test_normal.vim
@@ -2353,19 +2353,19 @@ func Test_normal30_changecase()
   norm! 1ggVu
   call assert_equal('this is a simple test: äüöß', getline('.'))
   norm! VU
-  call assert_equal('THIS IS A SIMPLE TEST: ÄÜÖSS', getline('.'))
+  call assert_equal('THIS IS A SIMPLE TEST: ÄÜÖẞ', getline('.'))
   norm! guu
-  call assert_equal('this is a simple test: äüöss', getline('.'))
+  call assert_equal('this is a simple test: äüöß', getline('.'))
   norm! gUgU
-  call assert_equal('THIS IS A SIMPLE TEST: ÄÜÖSS', getline('.'))
+  call assert_equal('THIS IS A SIMPLE TEST: ÄÜÖẞ', getline('.'))
   norm! gugu
-  call assert_equal('this is a simple test: äüöss', getline('.'))
+  call assert_equal('this is a simple test: äüöß', getline('.'))
   norm! gUU
-  call assert_equal('THIS IS A SIMPLE TEST: ÄÜÖSS', getline('.'))
+  call assert_equal('THIS IS A SIMPLE TEST: ÄÜÖẞ', getline('.'))
   norm! 010~
-  call assert_equal('this is a SIMPLE TEST: ÄÜÖSS', getline('.'))
+  call assert_equal('this is a SIMPLE TEST: ÄÜÖẞ', getline('.'))
   norm! V~
-  call assert_equal('THIS IS A simple test: äüöss', getline('.'))
+  call assert_equal('THIS IS A simple test: äüöß', getline('.'))
   call assert_beeps('norm! c~')
   %d
   call assert_beeps('norm! ~')
diff --git a/test/old/testdir/test_utf8_comparisons.vim b/test/old/testdir/test_utf8_comparisons.vim
index f3c86b44fb..20b5762c9d 100644
--- a/test/old/testdir/test_utf8_comparisons.vim
+++ b/test/old/testdir/test_utf8_comparisons.vim
@@ -92,3 +92,40 @@ func Test_gap()
   call feedkeys("gg0g~ap", "tx")
   call assert_equal(["ABCD", "", "defg"], getline(1,3))
 endfunc
+
+" test that g~, ~ and gU correclty upper-cases ß
+func Test_uppercase_sharp_ss()
+  new
+  call setline(1, repeat(['ß'], 4))
+
+  call cursor(1, 1)
+  norm! ~
+  call assert_equal('ẞ', getline(line('.')))
+  norm! ~
+  call assert_equal('ß', getline(line('.')))
+
+  call cursor(2, 1)
+  norm! g~l
+  call assert_equal('ẞ', getline(line('.')))
+  norm! g~l
+  call assert_equal('ß', getline(line('.')))
+
+  call cursor(3, 1)
+  norm! gUl
+  call assert_equal('ẞ', getline(line('.')))
+  norm! vgU
+  call assert_equal('ẞ', getline(line('.')))
+  norm! vgu
+  call assert_equal('ß', getline(line('.')))
+  norm! gul
+  call assert_equal('ß', getline(line('.')))
+
+  call cursor(4, 1)
+  norm! vgU
+  call assert_equal('ẞ', getline(line('.')))
+  norm! vgu
+  call assert_equal('ß', getline(line('.')))
+  bw!
+endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab
diff --git a/test/old/testdir/test_visual.vim b/test/old/testdir/test_visual.vim
index 983f07a375..94b8009534 100644
--- a/test/old/testdir/test_visual.vim
+++ b/test/old/testdir/test_visual.vim
@@ -1022,9 +1022,9 @@ func Test_visual_change_case()
   exe "normal Oblah di\rdoh dut\<Esc>VkUj\r"
   " Uppercase part of two lines
   exe "normal ddppi333\<Esc>k0i222\<Esc>fyllvjfuUk"
-  call assert_equal(['the YOUTUSSEUU end', '- yOUSSTUSSEXu -',
-        \ 'THE YOUTUSSEUU END', '111THE YOUTUSSEUU END', 'BLAH DI', 'DOH DUT',
-        \ '222the yoUTUSSEUU END', '333THE YOUTUßeuu end'], getline(2, '$'))
+  call assert_equal(['the YOUTUẞEUU end', '- yOUẞTUẞEXu -',
+        \ 'THE YOUTUẞEUU END', '111THE YOUTUẞEUU END', 'BLAH DI', 'DOH DUT',
+        \ '222the yoUTUẞEUU END', '333THE YOUTUßeuu end'], getline(2, '$'))
   bwipe!
 endfunc