feat: resolve help tags ourselves in cmdline

Closes #631

lua/blink/cmp/lib/async.lua

@@ -151,7 +151,9 @@ end
 --- utils
 
 function task.await_all(tasks)
-  if #tasks == 0 then return task.empty() end
+  if #tasks == 0 then
+    return task.new(function(resolve) resolve({}) end)
+  end
 
   local all_task
   all_task = task.new(function(resolve, reject)

lua/blink/cmp/sources/cmdline/help.lua

@@ -0,0 +1,47 @@
+local async = require('blink.cmp.lib.async')
+
+local help = {}
+
+--- Processes a help file and returns a list of tags asynchronously
+--- @param file string
+--- @return blink.cmp.Task
+--- TODO: rewrite using async lib, shared as a library in lib/fs.lua
+local function read_tags_from_file(file)
+  return async.task.new(function(resolve)
+    vim.uv.fs_open(file, 'r', 438, function(err, fd)
+      if err or fd == nil then return resolve({}) end
+
+      -- Read file content
+      vim.uv.fs_fstat(fd, function(stat_err, stat)
+        if stat_err or stat == nil then
+          vim.uv.fs_close(fd)
+          return resolve({})
+        end
+
+        vim.uv.fs_read(fd, stat.size, 0, function(read_err, data)
+          vim.uv.fs_close(fd)
+
+          if read_err or data == nil then return resolve({}) end
+
+          -- Process the file content
+          local tags = {}
+          for line in data:gmatch('[^\r\n]+') do
+            local tag = line:match('^([^\t]+)')
+            if tag then table.insert(tags, tag) end
+          end
+
+          resolve(tags)
+        end)
+      end)
+    end)
+  end)
+end
+
+function help.get_completions()
+  local help_files = vim.api.nvim_get_runtime_file('doc/tags', true)
+  return async.task
+    .await_all(vim.tbl_map(read_tags_from_file, help_files))
+    :map(function(results) return require('blink.cmp.lib.utils').flatten(results) end)
+end
+
+return help

lua/blink/cmp/sources/cmdline/init.lua

@@ -2,6 +2,8 @@
 -- https://github.com/hrsh7th/cmp-cmdline
 -- License: MIT
 
+local async = require('blink.cmp.lib.async')
+
 --- @class blink.cmp.Source
 local cmdline = {}
 
@@ -31,39 +33,56 @@ function cmdline:get_completions(context, callback)
   )
   local current_arg_prefix = current_arg:sub(1, keyword.start_col - #text_before_cursor - 1)
 
-  local query = (text_before_cursor .. current_arg_prefix):gsub([[\\]], [[\\\\]])
-  local completions = vim.fn.getcompletion(query, 'cmdline')
+  local task = async.task
+    .empty()
+    :map(function()
+      -- Special case for help where we read all the tags ourselves
+      if vim.tbl_contains({ 'h', 'he', 'hel', 'help' }, arguments[1] or '') then
+        return require('blink.cmp.sources.cmdline.help').get_completions()
+      end
+
+      local query = (text_before_cursor .. current_arg_prefix):gsub([[\\]], [[\\\\]])
+      return vim.fn.getcompletion(query, 'cmdline')
+    end)
+    :map(function(completions)
+      local items = {}
+      for _, completion in ipairs(completions) do
+        -- remove prefix from the label
+        if string.find(completion, current_arg_prefix, 1, true) == 1 then
+          completion = completion:sub(#current_arg_prefix + 1)
+        end
 
-  local items = {}
-  for _, completion in ipairs(completions) do
-    -- remove prefix from the label
-    if string.find(completion, current_arg_prefix, 1, true) == 1 then
-      completion = completion:sub(#current_arg_prefix + 1)
-    end
+        -- add prefix to the newText
+        local new_text = completion
+        if string.find(new_text, current_arg_prefix, 1, true) ~= 1 then new_text = current_arg_prefix .. completion end
 
-    -- add prefix to the newText
-    local new_text = completion
-    if string.find(new_text, current_arg_prefix, 1, true) ~= 1 then new_text = current_arg_prefix .. completion end
+        table.insert(items, {
+          label = completion,
+          insertText = completion,
+          sortText = completion,
+          textEdit = {
+            newText = new_text,
+            range = {
+              start = { line = 0, character = #text_before_cursor },
+              ['end'] = { line = 0, character = #text_before_cursor + #current_arg },
+            },
+          },
+          kind = require('blink.cmp.types').CompletionItemKind.Property,
+        })
+      end
 
-    table.insert(items, {
-      label = completion,
-      insertText = completion,
-      textEdit = {
-        newText = new_text,
-        range = {
-          start = { line = 0, character = #text_before_cursor },
-          ['end'] = { line = 0, character = #text_before_cursor + #current_arg },
-        },
-      },
-      kind = require('blink.cmp.types').CompletionItemKind.Property,
-    })
-  end
+      callback({
+        is_incomplete_backward = true,
+        is_incomplete_forward = false,
+        items = items,
+      })
+    end)
+    :catch(function(err)
+      vim.notify('Error while fetching completions: ' .. err, vim.log.levels.ERROR)
+      callback({ is_incomplete_backward = false, is_incomplete_forward = false, items = {} })
+    end)
 
-  callback({
-    is_incomplete_backward = false,
-    is_incomplete_forward = false,
-    items = items,
-  })
+  return function() task:cancel() end
 end
 
 return cmdline