feat(lsp): allow passing custom list handler to LSP functions that return lists (#19213)

Currently LSP allows only using loclist or quickfix list window. I
normally prefer to review all quickfix items without opening quickfix
window. This fix allows passing `on_list` option which allows full
control what to do with list.

Here is example how to use it with quick fix list:

```lua
local function on_list(options)
  vim.fn.setqflist({}, ' ', options)
  vim.api.nvim_command('cfirst')
end

local bufopts = { noremap=true, silent=true, buffer=bufnr }
vim.keymap.set('n', '<leader>ad', function() vim.lsp.buf.declaration{on_list=on_list} end, bufopts)
vim.keymap.set('n', '<leader>d', function() vim.lsp.buf.definition{on_list=on_list} end, bufopts)
vim.keymap.set('n', '<leader>ai', function() vim.lsp.buf.implementation{on_list=on_list} end, bufopts)
vim.keymap.set('n', '<leader>at', function() vim.lsp.buf.type_definition{on_list=on_list} end, bufopts)
vim.keymap.set('n', '<leader>af', function() vim.lsp.buf.references(nil, {on_list=on_list}) end, bufopts)
```

If you prefer loclist do something like this:

```lua
local function on_list(options)
  vim.fn.setloclist(0, {}, ' ', options)
  vim.api.nvim_command('lopen')
end
```

close #19182

Co-authored-by: Mathias Fußenegger <mfussenegger@users.noreply.github.com>

1 files changed, 26 insertions, 25 deletions

diff --git a/runtime/lua/vim/lsp/handlers.lua b/runtime/lua/vim/lsp/handlers.lua
index 3b869d8f5c..cfc35f0b51 100644
--- a/runtime/lua/vim/lsp/handlers.lua
+++ b/runtime/lua/vim/lsp/handlers.lua
@@ -189,19 +189,17 @@ M['textDocument/references'] = function(_, result, ctx, config)
   else
     local client = vim.lsp.get_client_by_id(ctx.client_id)
     config = config or {}
+    local title = 'References'
+    local items = util.locations_to_items(result, client.offset_encoding)
+
     if config.loclist then
-      vim.fn.setloclist(0, {}, ' ', {
-        title = 'References',
-        items = util.locations_to_items(result, client.offset_encoding),
-        context = ctx,
-      })
+      vim.fn.setloclist(0, {}, ' ', { title = title, items = items, context = ctx })
       api.nvim_command('lopen')
+    elseif config.on_list then
+      assert(type(config.on_list) == 'function', 'on_list is not a function')
+      config.on_list({ title = title, items = items, context = ctx })
     else
-      vim.fn.setqflist({}, ' ', {
-        title = 'References',
-        items = util.locations_to_items(result, client.offset_encoding),
-        context = ctx,
-      })
+      vim.fn.setqflist({}, ' ', { title = title, items = items, context = ctx })
       api.nvim_command('botright copen')
     end
   end
@@ -224,19 +222,17 @@ local function response_to_list(map_result, entity, title_fn)
       vim.notify('No ' .. entity .. ' found')
     else
       config = config or {}
+      local title = title_fn(ctx)
+      local items = map_result(result, ctx.bufnr)
+
       if config.loclist then
-        vim.fn.setloclist(0, {}, ' ', {
-          title = title_fn(ctx),
-          items = map_result(result, ctx.bufnr),
-          context = ctx,
-        })
+        vim.fn.setloclist(0, {}, ' ', { title = title, items = items, context = ctx })
         api.nvim_command('lopen')
+      elseif config.on_list then
+        assert(type(config.on_list) == 'function', 'on_list is not a function')
+        config.on_list({ title = title, items = items, context = ctx })
       else
-        vim.fn.setqflist({}, ' ', {
-          title = title_fn(ctx),
-          items = map_result(result, ctx.bufnr),
-          context = ctx,
-        })
+        vim.fn.setqflist({}, ' ', { title = title, items = items, context = ctx })
         api.nvim_command('botright copen')
       end
     end
@@ -354,11 +350,16 @@ local function location_handler(_, result, ctx, config)
     util.jump_to_location(result[1], client.offset_encoding, config.reuse_win)
 
     if #result > 1 then
-      vim.fn.setqflist({}, ' ', {
-        title = 'LSP locations',
-        items = util.locations_to_items(result, client.offset_encoding),
-      })
-      api.nvim_command('botright copen')
+      local title = 'LSP locations'
+      local items = util.locations_to_items(result, client.offset_encoding)
+
+      if config.on_list then
+        assert(type(config.on_list) == 'function', 'on_list is not a function')
+        config.on_list({ title = title, items = items })
+      else
+        vim.fn.setqflist({}, ' ', { title = title, items = items })
+        api.nvim_command('botright copen')
+      end
     end
   else
     util.jump_to_location(result, client.offset_encoding, config.reuse_win)