feat(snippet): set snippet keymaps permanent instead of dynamic (#31887)

Problem:

Given that `vim.snippet.expand()` sets temporary `<tab>`/`<s-tab>`
keymaps there is no way to build "smart-tab" functionality where `<tab>`
chooses the next completion candidate if the popup menu is visible.

Solution:

Set the keymap permanent in `_defaults`.

The downside of this approach is that users of multiple snippet engine's
need to adapt their keymaps to handle all their engines that are in use.
For example:

    vim.keymap.set({ 'i', 's' }, "<Tab>", function()
      if foreign_snippet.active() then
        return "<Cmd>lua require('foreign_snippet').jump()<CR>"
      elseif vim.snippet.active({ direction = 1 }) then
        return "<Cmd>lua vim.snippet.jump(1)<CR>"
      else
        return key
      end
    end, { expr = true })

Upside is that using `vim.keymap.set` to override keymaps is a well
established pattern and `vim.snippet.expand` calls made by nvim itself
or plugins have working keymaps out of the box.


Co-authored-by: Maria José Solano <majosolano99@gmail.com>

1 files changed, 2 insertions, 73 deletions

diff --git a/runtime/lua/vim/snippet.lua b/runtime/lua/vim/snippet.lua
index bfd439181e..2edea6d5ad 100644
--- a/runtime/lua/vim/snippet.lua
+++ b/runtime/lua/vim/snippet.lua
@@ -2,8 +2,6 @@ local G = vim.lsp._snippet_grammar
 local snippet_group = vim.api.nvim_create_augroup('nvim.snippet', {})
 local snippet_ns = vim.api.nvim_create_namespace('nvim.snippet')
 local hl_group = 'SnippetTabstop'
-local jump_forward_key = '<tab>'
-local jump_backward_key = '<s-tab>'
 
 --- Returns the 0-based cursor position.
 ---
@@ -213,64 +211,9 @@ function Session.new(bufnr, snippet_extmark, tabstop_data)
     end
   end
 
-  self:set_keymaps()
-
   return self
 end
 
---- Sets the snippet navigation keymaps.
----
---- @package
-function Session:set_keymaps()
-  local function maparg(key, mode)
-    local map = vim.fn.maparg(key, mode, false, true) --[[ @as table ]]
-    if not vim.tbl_isempty(map) and map.buffer == 1 then
-      return map
-    else
-      return nil
-    end
-  end
-
-  local function set(jump_key, direction)
-    vim.keymap.set({ 'i', 's' }, jump_key, function()
-      return vim.snippet.active({ direction = direction })
-          and '<cmd>lua vim.snippet.jump(' .. direction .. ')<cr>'
-        or jump_key
-    end, { expr = true, silent = true, buffer = self.bufnr })
-  end
-
-  self.tab_keymaps = {
-    i = maparg(jump_forward_key, 'i'),
-    s = maparg(jump_forward_key, 's'),
-  }
-  self.shift_tab_keymaps = {
-    i = maparg(jump_backward_key, 'i'),
-    s = maparg(jump_backward_key, 's'),
-  }
-  set(jump_forward_key, 1)
-  set(jump_backward_key, -1)
-end
-
---- Restores/deletes the keymaps used for snippet navigation.
----
---- @package
-function Session:restore_keymaps()
-  local function restore(keymap, lhs, mode)
-    if keymap then
-      vim._with({ buf = self.bufnr }, function()
-        vim.fn.mapset(keymap)
-      end)
-    else
-      vim.api.nvim_buf_del_keymap(self.bufnr, mode, lhs)
-    end
-  end
-
-  restore(self.tab_keymaps.i, jump_forward_key, 'i')
-  restore(self.tab_keymaps.s, jump_forward_key, 's')
-  restore(self.shift_tab_keymaps.i, jump_backward_key, 'i')
-  restore(self.shift_tab_keymaps.s, jump_backward_key, 's')
-end
-
 --- Returns the destination tabstop index when jumping in the given direction.
 ---
 --- @package
@@ -604,7 +547,7 @@ end
 
 --- Jumps to the next (or previous) placeholder in the current snippet, if possible.
 ---
---- For example, map `<Tab>` to jump while a snippet is active:
+--- By default `<Tab>` is setup to jump if a snippet is active. The default mapping looks like:
 ---
 --- ```lua
 --- vim.keymap.set({ 'i', 's' }, '<Tab>', function()
@@ -613,7 +556,7 @@ end
 ---    else
 ---      return '<Tab>'
 ---    end
----  end, { expr = true })
+---  end, { descr = '...', expr = true, silent = true })
 --- ```
 ---
 --- @param direction (vim.snippet.Direction) Navigation direction. -1 for previous, 1 for next.
@@ -656,18 +599,6 @@ end
 --- Returns `true` if there's an active snippet in the current buffer,
 --- applying the given filter if provided.
 ---
---- You can use this function to navigate a snippet as follows:
----
---- ```lua
---- vim.keymap.set({ 'i', 's' }, '<Tab>', function()
----    if vim.snippet.active({ direction = 1 }) then
----      return '<Cmd>lua vim.snippet.jump(1)<CR>'
----    else
----      return '<Tab>'
----    end
----  end, { expr = true })
---- ```
----
 --- @param filter? vim.snippet.ActiveFilter Filter to constrain the search with:
 --- - `direction` (vim.snippet.Direction): Navigation direction. Will return `true` if the snippet
 --- can be jumped in the given direction.
@@ -689,8 +620,6 @@ function M.stop()
     return
   end
 
-  M._session:restore_keymaps()
-
   vim.api.nvim_clear_autocmds({ group = snippet_group, buffer = M._session.bufnr })
   vim.api.nvim_buf_clear_namespace(M._session.bufnr, snippet_ns, 0, -1)