feat: --expect improvements with upcoming fzf 0.53

Once fzf 0.53 is releases adding fzf prefix for actions will become
much easier due to junegunn/fzf#3810

A few examples below.

Adding a prefix to an already existing action (`alt-q` send to quickfix):
```lua
:FzfLua live_grep keymap.fzf.alt-q=select-all
```

Using a different (or custom) action:
```lua
:lua require("fzf-lua").files({
  actions ={
    ["ctrl-q"] = { fn = require"fzf-lua".actions.file_sel_to_qf, prefix = "select-all+accept" }
  }
})
```

lua/fzf-lua/actions.lua

@@ -8,18 +8,29 @@ local M = {}
 local _default_action = "default"
 
 -- return fzf '--expect=' string from actions keyval tbl
-M.expect = function(actions)
+-- on fzf >= 0.53 add the `prefix` key to the bind flags
+M.expect = function(actions, _)
   if not actions then return nil end
   local keys = {}
+  local binds = {}
   for k, v in pairs(actions) do
-    if k ~= _default_action and v ~= false then
+    local is_default = k == _default_action
+    if not is_default and v ~= false then
       table.insert(keys, k)
     end
+    -- Although this only works in fzf 0.53 we don't need to limit the use of these
+    -- actions as `--expect` precets the bind and thus the extra bind has no effect
+    if type(v) == "table" and type(v.prefix) == "string" then
+      table.insert(binds, string.format("%s:%s%s",
+        is_default and "enter" or k,
+        -- When used with `--expect` "accept" is implied and "+" is erroneous
+        v.prefix:gsub("accept$", ""):gsub("%+$", ""),
+        -- Since default accept bind (enter) is excluded from `--expect`
+        -- we need to add "+accept" to complete the selection and exit fzf
+        is_default and "+accept" or ""))
+    end
   end
-  if #keys > 0 then
-    return table.concat(keys, ",")
-  end
-  return nil
+  return #keys > 0 and keys or nil, #binds > 0 and binds or nil
 end
 
 M.normalize_selected = function(actions, selected)

lua/fzf-lua/core.lua

@@ -592,7 +592,22 @@ M.build_fzf_cli = function(opts)
   end
   opts.fzf_opts["--bind"] = M.create_fzf_binds(opts.keymap.fzf)
   opts.fzf_opts["--color"] = M.create_fzf_colors(opts)
-  opts.fzf_opts["--expect"] = actions.expect(opts.actions)
+  do
+    -- `actions.expect` parses the actions table and returns a list of
+    -- keys that trigger completion (accept) to be added to `--expect`
+    -- If the action contains the prefix key, e.g. `{ fn = ... , prefix = "select-all" }`
+    -- additional binds will be set for the specific action key
+    -- NOTE: requires fzf >= 0.53 (https://github.com/junegunn/fzf/issues/3810)
+    local expect_keys, expect_binds = actions.expect(opts.actions, opts)
+    if expect_keys and #expect_keys > 0 then
+      opts.fzf_opts["--expect"] = table.concat(expect_keys, ",")
+    end
+    if expect_binds and #expect_binds > 0 then
+      local bind = opts.fzf_opts["--bind"]
+      opts.fzf_opts["--bind"] = string.format("%s%s%s",
+        bind, bind and "," or "", table.concat(expect_binds, ","))
+    end
+  end
   if opts.fzf_opts["--preview-window"] == nil then
     opts.fzf_opts["--preview-window"] = M.preview_window(opts)
   end
@@ -878,7 +893,9 @@ M.set_header = function(opts, hdr_tbl)
         if type(opts.regex_filter) == "string" then
           return opts.regex_filter
         elseif type(opts.regex_filter) == "table" and type(opts.regex_filter[1]) == "string" then
-          return string.format("%s%s", opts.regex_filter.exclude and "not " or "", opts.regex_filter[1])
+          return string.format("%s%s",
+            opts.regex_filter.exclude and "not " or "",
+            opts.regex_filter[1])
         elseif type(opts.regex_filter) == "function" then
           return "<function>"
         end