feat(edit): insert an unsimplified key using CTRL-SHIFT-V

This marks the following Vim patches as ported:

vim-patch:8.1.2333: with modifyOtherKeys CTRL-^ doesn't work

Problem:    With modifyOtherKeys CTRL-^ doesn't work.
Solution:   Handle the exception.
https://github.com/vim/vim/commit/828ffd596394f714270a01a55fc3f949a8bd9b35

vim-patch:8.1.2350: other text for CTRL-V in Insert mode with modifyOtherKeys

Problem:    Other text for CTRL-V in Insert mode with modifyOtherKeys.
Solution:   Convert the Escape sequence back to key as if modifyOtherKeys is
            not set, and use CTRL-SHIFT-V to get the Escape sequence itself.
            (closes vim/vim#5254)
https://github.com/vim/vim/commit/fc4ea2a72d36de1196a3ce17352e72f8fe90f4bb

vim-patch:8.2.2084: CTRL-V U doesn't work to enter a Unicode character

Problem:    CTRL-V U doesn't work to enter a Unicode character when
            modifyOtherKeys is effective. (Ken Takata)
Solution:   Add a flag to get_literal() for the shift key. (closes vim/vim#7413)
https://github.com/vim/vim/commit/0684e36a7ee0743f2889698fb8e0e14f7acae423

Omit getcmdkeycmd() change as it depends on Vim patch 8.2.2062, which
may introduce a potential breakage.

8 files changed, 118 insertions, 76 deletions

diff --git a/runtime/doc/cmdline.txt b/runtime/doc/cmdline.txt
index 9fa2034718..6228c9238f 100644
--- a/runtime/doc/cmdline.txt
+++ b/runtime/doc/cmdline.txt
@@ -67,12 +67,19 @@ CTRL-V		Insert next non-digit literally.  Up to three digits form the
 		decimal value of a single byte.  The non-digit and the three
 		digits are not considered for mapping.  This works the same
 		way as in Insert mode (see above, |i_CTRL-V|).
+		For special keys, the CTRL modifier may be included into the
+		key to produce a control character.  If there is no control
+		character for the key then its |key-notation| is inserted.
 		Note: Under Windows CTRL-V is often mapped to paste text.
 		Use CTRL-Q instead then.
 							*c_CTRL-Q*
 CTRL-Q		Same as CTRL-V.  But with some terminals it is used for
 		control flow, it doesn't work then.
 
+CTRL-SHIFT-V				*c_CTRL-SHIFT-V* *c_CTRL-SHIFT-Q*
+CTRL-SHIFT-Q	Works just like CTRL-V, but do not try to include the CTRL
+		modifier into the key.
+
 							*c_<Left>* *c_Left*
 <Left>		cursor left
 							*c_<Right>* *c_Right*
diff --git a/runtime/doc/insert.txt b/runtime/doc/insert.txt
index 9db44eaaa0..7f6662089d 100644
--- a/runtime/doc/insert.txt
+++ b/runtime/doc/insert.txt
@@ -192,12 +192,14 @@ CTRL-D		Delete one shiftwidth of indent at the start of the current
 		label.
 
 						*i_CTRL-V*
-CTRL-V		Insert next non-digit literally.  For special keys, the
-		terminal code is inserted.  It's also possible to enter the
-		decimal, octal or hexadecimal value of a character
+CTRL-V		Insert next non-digit literally.  It's also possible to enter
+		the decimal, octal or hexadecimal value of a character
 		|i_CTRL-V_digit|.
 		The characters typed right after CTRL-V are not considered for
 		mapping.
+		For special keys, the CTRL modifier may be included into the
+		key to produce a control character.  If there is no control
+		character for the key then its |key-notation| is inserted.
 		Note: When CTRL-V is mapped (e.g., to paste text) you can
 		often use CTRL-Q instead |i_CTRL-Q|.
 
@@ -206,6 +208,10 @@ CTRL-Q		Same as CTRL-V.
 		Note: Some terminal connections may eat CTRL-Q, it doesn't
 		work then.  It does work in the GUI.
 
+CTRL-SHIFT-V				*i_CTRL-SHIFT-V* *i_CTRL-SHIFT-Q*
+CTRL-SHIFT-Q	Works just like CTRL-V, but do not try to include the CTRL
+		modifier into the key.
+
 CTRL-X		Enter CTRL-X mode.  This is a sub-mode where commands can
 		be given to complete words or scroll the window.  See
 		|i_CTRL-X| and |ins-completion|.
diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 48436f1115..3e3648e61f 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -1587,7 +1587,8 @@ static void ins_ctrl_v(void)
 
   add_to_showcmd_c(Ctrl_V);
 
-  c = get_literal();
+  // Do not include modifiers into the key for CTRL-SHIFT-V.
+  c = get_literal(mod_mask & MOD_MASK_SHIFT);
   if (did_putchar) {
     // when the line fits in 'columns' the '^' is at the start of the next
     // line and will not removed by the redraw
@@ -5612,13 +5613,13 @@ static unsigned quote_meta(char_u *dest, char_u *src, int len)
   return m;
 }
 
-/*
- * Next character is interpreted literally.
- * A one, two or three digit decimal number is interpreted as its byte value.
- * If one or two digits are entered, the next character is given to vungetc().
- * For Unicode a character > 255 may be returned.
- */
-int get_literal(void)
+/// Next character is interpreted literally.
+/// A one, two or three digit decimal number is interpreted as its byte value.
+/// If one or two digits are entered, the next character is given to vungetc().
+/// For Unicode a character > 255 may be returned.
+///
+/// @param  no_simplify  do not include modifiers into the key
+int get_literal(bool no_simplify)
 {
   int cc;
   int nc;
@@ -5636,6 +5637,9 @@ int get_literal(void)
   i = 0;
   for (;;) {
     nc = plain_vgetc();
+    if (!no_simplify) {
+      nc = merge_modifiers(nc);
+    }
     if ((mod_mask & ~MOD_MASK_SHIFT) != 0) {
       // A character with non-Shift modifiers should not be a valid
       // character for i_CTRL-V_digit.
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index b7d75855d6..ea5bfc9a36 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -2208,7 +2208,11 @@ static int command_line_handle_key(CommandLineState *s)
   case Ctrl_Q:
     s->ignore_drag_release = true;
     putcmdline('^', true);
-    s->c = get_literal();                 // get next (two) character(s)
+
+    // Get next (two) characters.
+    // Do not include modifiers into the key for CTRL-SHIFT-V.
+    s->c = get_literal(mod_mask & MOD_MASK_SHIFT);
+
     s->do_abbr = false;                   // don't do abbreviation now
     ccline.special_char = NUL;
     // may need to remove ^ when composing char was typed
diff --git a/src/nvim/getchar.c b/src/nvim/getchar.c
index b25c59636f..f92aa14c78 100644
--- a/src/nvim/getchar.c
+++ b/src/nvim/getchar.c
@@ -1442,6 +1442,27 @@ static void updatescript(int c)
   }
 }
 
+/// Merge "mod_mask" into "c_arg"
+int merge_modifiers(int c_arg)
+{
+  int c = c_arg;
+
+  if (mod_mask & MOD_MASK_CTRL) {
+    if ((c >= '`' && c <= 0x7f) || (c >= '@' && c <= '_')) {
+      c &= 0x1f;
+      mod_mask &= ~MOD_MASK_CTRL;
+      if (c == 0) {
+        c = K_ZERO;
+      }
+    } else if (c == '6') {
+      // CTRL-6 is equivalent to CTRL-^
+      c = 0x1e;
+      mod_mask &= ~MOD_MASK_CTRL;
+    }
+  }
+  return c;
+}
+
 /// Get the next input character.
 /// Can return a special key or a multi-byte character.
 /// Can return NUL when called recursively, use safe_vgetc() if that's not
@@ -1603,19 +1624,7 @@ int vgetc(void)
 
       // A modifier was not used for a mapping, apply it to ASCII
       // keys.  Shift would already have been applied.
-      if (mod_mask & MOD_MASK_CTRL) {
-        if ((c >= '`' && c <= 0x7f) || (c >= '@' && c <= '_')) {
-          c &= 0x1f;
-          mod_mask &= ~MOD_MASK_CTRL;
-          if (c == 0) {
-            c = K_ZERO;
-          }
-        } else if (c == '6') {
-          // CTRL-6 is equivalent to CTRL-^
-          c = 0x1e;
-          mod_mask &= ~MOD_MASK_CTRL;
-        }
-      }
+      c = merge_modifiers(c);
 
       // If mappings are enabled (i.e., not Ctrl-v) and the user directly typed
       // something with a meta- or alt- modifier that was not mapped, interpret
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index ed5f13d00a..73ea995d8f 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -5154,7 +5154,7 @@ static void nv_replace(cmdarg_T *cap)
   // get another character
   if (cap->nchar == Ctrl_V) {
     had_ctrl_v = Ctrl_V;
-    cap->nchar = get_literal();
+    cap->nchar = get_literal(false);
     // Don't redo a multibyte character with CTRL-V.
     if (cap->nchar > DEL) {
       had_ctrl_v = NUL;
@@ -5369,7 +5369,7 @@ static void nv_vreplace(cmdarg_T *cap)
       emsg(_(e_modifiable));
     } else {
       if (cap->extra_char == Ctrl_V) {          // get another character
-        cap->extra_char = get_literal();
+        cap->extra_char = get_literal(false);
       }
       stuffcharReadbuff(cap->extra_char);
       stuffcharReadbuff(ESC);
diff --git a/test/functional/editor/mode_cmdline_spec.lua b/test/functional/editor/mode_cmdline_spec.lua
index 0f7d821bb5..50cc5e17ee 100644
--- a/test/functional/editor/mode_cmdline_spec.lua
+++ b/test/functional/editor/mode_cmdline_spec.lua
@@ -3,67 +3,74 @@
 local helpers = require('test.functional.helpers')(after_each)
 local clear, insert, funcs, eq, feed =
   helpers.clear, helpers.insert, helpers.funcs, helpers.eq, helpers.feed
+local eval = helpers.eval
 local meths = helpers.meths
 
-describe('cmdline CTRL-R', function()
+describe('cmdline', function()
   before_each(clear)
 
-  it('pasting non-special register inserts <CR> *between* lines', function()
-    insert([[
-    line1abc
-    line2somemoretext
-    ]])
-    -- Yank 2 lines linewise, then paste to cmdline.
-    feed([[<C-\><C-N>gg0yj:<C-R>0]])
-    -- <CR> inserted between lines, NOT after the final line.
-    eq('line1abc\rline2somemoretext', funcs.getcmdline())
+  describe('Ctrl-R', function()
+    it('pasting non-special register inserts <CR> *between* lines', function()
+      insert([[
+      line1abc
+      line2somemoretext
+      ]])
+      -- Yank 2 lines linewise, then paste to cmdline.
+      feed([[<C-\><C-N>gg0yj:<C-R>0]])
+      -- <CR> inserted between lines, NOT after the final line.
+      eq('line1abc\rline2somemoretext', funcs.getcmdline())
 
-    -- Yank 2 lines charwise, then paste to cmdline.
-    feed([[<C-\><C-N>gg05lyvj:<C-R>0]])
-    -- <CR> inserted between lines, NOT after the final line.
-    eq('abc\rline2', funcs.getcmdline())
+      -- Yank 2 lines charwise, then paste to cmdline.
+      feed([[<C-\><C-N>gg05lyvj:<C-R>0]])
+      -- <CR> inserted between lines, NOT after the final line.
+      eq('abc\rline2', funcs.getcmdline())
 
-    -- Yank 1 line linewise, then paste to cmdline.
-    feed([[<C-\><C-N>ggyy:<C-R>0]])
-    -- No <CR> inserted.
-    eq('line1abc', funcs.getcmdline())
-  end)
+      -- Yank 1 line linewise, then paste to cmdline.
+      feed([[<C-\><C-N>ggyy:<C-R>0]])
+      -- No <CR> inserted.
+      eq('line1abc', funcs.getcmdline())
+    end)
 
-  it('pasting special register inserts <CR>, <NL>', function()
-    feed([[:<C-R>="foo\nbar\rbaz"<CR>]])
-    eq('foo\nbar\rbaz', funcs.getcmdline())
+    it('pasting special register inserts <CR>, <NL>', function()
+      feed([[:<C-R>="foo\nbar\rbaz"<CR>]])
+      eq('foo\nbar\rbaz', funcs.getcmdline())
+    end)
   end)
-end)
 
-describe('cmdline history', function()
-  before_each(clear)
+  it('Ctrl-Shift-V supports entering unsimplified key notations', function()
+    feed(':"<C-S-V><C-J><C-S-V><C-@><C-S-V><C-[><C-S-V><C-S-M><C-S-V><M-C-I><C-S-V><C-D-J><CR>')
 
-  it('correctly clears start of the history', function()
-    -- Regression test: check absence of the memory leak when clearing start of
-    -- the history using ex_getln.c/clr_history().
-    eq(1, funcs.histadd(':', 'foo'))
-    eq(1, funcs.histdel(':'))
-    eq('', funcs.histget(':', -1))
+    eq('"<C-J><C-@><C-[><C-S-M><M-C-I><C-D-J>', eval('@:'))
   end)
 
-  it('correctly clears end of the history', function()
-    -- Regression test: check absence of the memory leak when clearing end of
-    -- the history using ex_getln.c/clr_history().
-    meths.set_option('history', 1)
-    eq(1, funcs.histadd(':', 'foo'))
-    eq(1, funcs.histdel(':'))
-    eq('', funcs.histget(':', -1))
-  end)
+  describe('history', function()
+    it('correctly clears start of the history', function()
+      -- Regression test: check absence of the memory leak when clearing start of
+      -- the history using ex_getln.c/clr_history().
+      eq(1, funcs.histadd(':', 'foo'))
+      eq(1, funcs.histdel(':'))
+      eq('', funcs.histget(':', -1))
+    end)
+
+    it('correctly clears end of the history', function()
+      -- Regression test: check absence of the memory leak when clearing end of
+      -- the history using ex_getln.c/clr_history().
+      meths.set_option('history', 1)
+      eq(1, funcs.histadd(':', 'foo'))
+      eq(1, funcs.histdel(':'))
+      eq('', funcs.histget(':', -1))
+    end)
 
-  it('correctly removes item from history', function()
-    -- Regression test: check that ex_getln.c/del_history_idx() correctly clears
-    -- history index after removing history entry. If it does not then deleting
-    -- history will result in a double free.
-    eq(1, funcs.histadd(':', 'foo'))
-    eq(1, funcs.histadd(':', 'bar'))
-    eq(1, funcs.histadd(':', 'baz'))
-    eq(1, funcs.histdel(':', -2))
-    eq(1, funcs.histdel(':'))
-    eq('', funcs.histget(':', -1))
+    it('correctly removes item from history', function()
+      -- Regression test: check that ex_getln.c/del_history_idx() correctly clears
+      -- history index after removing history entry. If it does not then deleting
+      -- history will result in a double free.
+      eq(1, funcs.histadd(':', 'foo'))
+      eq(1, funcs.histadd(':', 'bar'))
+      eq(1, funcs.histadd(':', 'baz'))
+      eq(1, funcs.histdel(':', -2))
+      eq(1, funcs.histdel(':'))
+      eq('', funcs.histget(':', -1))
+    end)
   end)
 end)
diff --git a/test/functional/editor/mode_insert_spec.lua b/test/functional/editor/mode_insert_spec.lua
index c38acbe96a..684dee69db 100644
--- a/test/functional/editor/mode_insert_spec.lua
+++ b/test/functional/editor/mode_insert_spec.lua
@@ -131,6 +131,11 @@ describe('insert-mode', function()
     end)
   end)
 
+  it('Ctrl-Shift-V supports entering unsimplified key notations', function()
+    feed('i<C-S-V><C-J><C-S-V><C-@><C-S-V><C-[><C-S-V><C-S-M><C-S-V><M-C-I><C-S-V><C-D-J><Esc>')
+    expect('<C-J><C-@><C-[><C-S-M><M-C-I><C-D-J>')
+  end)
+
   describe([[With 'insertmode', Insert mode is not re-entered immediately after <C-L>]], function()
     before_each(function()
       command('set insertmode')