fix(keycodes): recognize <Find>, <Select> #28431

PuTTY sets TERM=xterm, but sends ESC[1~ and ESC[4~ for Home/End keys,
which does not match what the 'xterm' terminfo has for khome/kend, so
libtermkeys instead reports them as the original DEC VT220 names.

The VT220 came with a DEC LK201 keyboard which had the following keys in
the area above arrow keys (where PCs now have Ins/Del/Home/End/etc):

  ┌────────┬────────┬────────┐
  │ Find   │ Insert │ Re-    │
  │        │ Here   │ move   │
  ├────────┼────────┼────────┤
  │ Select │ Prev   │ Next   │
  │        │ Screen │ Screen │
  └────────┴────────┴────────┘

These would send ESC[x~ sequences in the expected order:

  ┌────────┬────────┬────────┐
  │ ESC[1~ │ ESC[2~ │ ESC[3~ │
  ├────────┼────────┼────────┤
  │ ESC[4~ │ ESC[5~ │ ESC[6~ │
  └────────┴────────┴────────┘

Modern terminals continue to use the same sequences for Ins/Del as well
as PageUp/PageDn. But the VT220 keyboard apparently had no Home/End, and
PuTTY apparently chose to re-purpose the Find/Select key sequences for
Home/End (even though it claims to emulate Xterm and this doesn't match
what actual Xterm does).

So when Home/End are used in Neovim through PuTTY with TERM=xterm (the
default setting), libtermkey finds no match for the received sequences
in the terminfo database and defaults to reporting them as <Find> and
<Select> respectively.

PuTTY is not unique here -- tmux *also* sends ESC[1~ and ESC[4~ after
its internal translation -- but the difference is that 'tmux' terminfo
correctly maps them to Home/End so Neovim recognizes them as such, while
PuTTY defaults to using 'xterm' which uses a different mapping.

This initial patch only allows Neovim to recognize <Find> and <Select>
key codes as themselves, so that the user could manually map them e.g.
using ":imap <Find> <Home>".

Alternatives:

  - Using TERM=putty(-256color) would of course be the most correct
    solution, but in practice it leads to other minor issues, e.g. the
    need to have different PuTTY config profiles for older or non-Linux
    systems that lack that terminfo, or tmux's insistence on rendering
    italics as reverse.

  - Using Neovim through tmux avoids the problem (as tmux recognizes
    ESC[1~ on input), but is something that needs to be manually run
    every time.

The keycodes.h constants are slightly misnamed because K_SELECT was
already taken for a different purpose.

4 files changed, 10 insertions, 0 deletions

diff --git a/runtime/doc/intro.txt b/runtime/doc/intro.txt
index 0c654b8b30..5cb969a531 100644
--- a/runtime/doc/intro.txt
+++ b/runtime/doc/intro.txt
@@ -272,6 +272,8 @@ notation        meaning             equivalent  decimal value(s)        ~
 <S-F1> - <S-F12> shift-function keys 1 to 12    *<S-F1>*
 <Help>          help key
 <Undo>          undo key
+<Find>          find key
+<Select>        select key
 <Insert>        insert key
 <Home>          home                            *home*
 <End>           end                             *end*
diff --git a/src/nvim/keycodes.c b/src/nvim/keycodes.c
index a9f8c9222a..b6ba73f7c1 100644
--- a/src/nvim/keycodes.c
+++ b/src/nvim/keycodes.c
@@ -261,6 +261,8 @@ static const struct key_name_entry {
 
   { K_HELP,            "Help" },
   { K_UNDO,            "Undo" },
+  { K_FIND,            "Find" },        // DEC key, often used as 'Home'
+  { K_KSELECT,         "Select" },      // DEC key, often used as 'End'
   { K_INS,             "Insert" },
   { K_INS,             "Ins" },         // Alternative name
   { K_KINS,            "kInsert" },
diff --git a/src/nvim/keycodes.h b/src/nvim/keycodes.h
index 5a7ddd4847..e24e30e7d0 100644
--- a/src/nvim/keycodes.h
+++ b/src/nvim/keycodes.h
@@ -352,6 +352,8 @@ enum key_extra {
 
 #define K_HELP          TERMCAP2KEY('%', '1')
 #define K_UNDO          TERMCAP2KEY('&', '8')
+#define K_FIND          TERMCAP2KEY('@', '0')   // DEC key, often used as Home
+#define K_KSELECT       TERMCAP2KEY('*', '6')   // DEC key, often used as End
 
 #define K_BS            TERMCAP2KEY('k', 'b')
 
diff --git a/test/functional/ui/input_spec.lua b/test/functional/ui/input_spec.lua
index 98312c42c9..bc1f3480e1 100644
--- a/test/functional/ui/input_spec.lua
+++ b/test/functional/ui/input_spec.lua
@@ -62,6 +62,8 @@ describe('mappings', function()
     add_mapping('<kenter>', '<kenter>')
     add_mapping('<kcomma>', '<kcomma>')
     add_mapping('<kequal>', '<kequal>')
+    add_mapping('<find>', '<find>')
+    add_mapping('<select>', '<select>')
     add_mapping('<f38>', '<f38>')
     add_mapping('<f63>', '<f63>')
   end)
@@ -130,6 +132,8 @@ describe('mappings', function()
     check_mapping('<KPComma>', '<kcomma>')
     check_mapping('<kequal>', '<kequal>')
     check_mapping('<KPEquals>', '<kequal>')
+    check_mapping('<Find>', '<find>')
+    check_mapping('<Select>', '<select>')
     check_mapping('<f38>', '<f38>')
     check_mapping('<f63>', '<f63>')
   end)