fix(help_tags): show help tags on windows (#3126)

On Windows, `builtin.help_tags` picker does not show any help tags.

To fix this, the following changes are needed:

1. `util.path_tail` checks unix separator `/` on Windows and leave the
original implementation intact on unix systems.

2. Line endings should be taken carefully on Windows. `vim.split` with
   only newline `\n` character as separator may result in unexpected
   crash when parsing large files. When splits on lines are needed, call
   it with `\r?\n`, or even set up a wrapper function in utils is more
   prefered.

Fixes #3126

lua/telescope/builtin/__internal.lua

@@ -729,7 +729,7 @@ internal.help_tags = function(opts)
   local delimiter = string.char(9)
   for _, lang in ipairs(langs) do
     for _, file in ipairs(tag_files[lang] or {}) do
-      local lines = vim.split(Path:new(file):read(), "\n", true)
+      local lines = vim.split(Path:new(file):read(), "\r?\n", { trimempty = true })
       for _, line in ipairs(lines) do
         -- TODO: also ignore tagComment starting with ';'
         if not line:match "^!_TAG_" then

lua/telescope/utils.lua

@@ -213,16 +213,30 @@ utils.path_smart = (function()
   end
 end)()
 
+-- vim.fn.fnamemodify(path, ":p:t") may replace util.path_tail(path),
+-- but the former may be slower and has dependency on neovim
 utils.path_tail = (function()
   local os_sep = utils.get_separator()
 
-  return function(path)
-    for i = #path, 1, -1 do
-      if path:sub(i, i) == os_sep then
-        return path:sub(i + 1, -1)
+  if os_sep == "/" then
+    return function(path)
+      for i = #path, 1, -1 do
+        if path:sub(i, i) == os_sep then
+          return path:sub(i + 1, -1)
+        end
       end
+      return path
+    end
+  else
+    return function(path)
+      for i = #path, 1, -1 do
+        local c = path:sub(i, i)
+        if c == os_sep or c == "/" then
+          return path:sub(i + 1, -1)
+        end
+      end
+      return path
     end
-    return path
   end
 end)()
 

lua/tests/automated/utils_spec.lua

@@ -307,3 +307,64 @@ describe("transform_path", function()
     end, new_relpath "doc/mydoc.md", new_relpath "d/mydoc.md")
   end)
 end)
+
+describe("path_tail", function()
+  local Path = require "plenary.path"
+  local old_sep = Path.path.sep
+
+  before_each(function()
+    Path.path.sep = old_sep
+  end)
+
+  local function setup_windows_sep()
+    Path.path.sep = [[\]]
+  end
+  local function setup_unix_sep()
+    Path.path.sep = "/"
+  end
+
+  local function assert_tails(paths)
+    for _, path in ipairs(paths) do
+      it("gets the tail of " .. path, function()
+        local tail = vim.fn.fnamemodify(path, ":p:t")
+        eq(tail, utils.path_tail(path))
+      end)
+    end
+  end
+
+  describe("handles windows paths", function()
+    local paths = {
+      [[C:\Users\username\AppData\Local\nvim-data\log]],
+      [[D:\Projects\project_folder\source_code.py]],
+      [[E:\Music\song.mp3]],
+      [[/home/usuario/documents/archivo.txt]],
+      [[/var/www/html/index.html]],
+      [[/mnt/backup/backup_file.tar.gz]],
+    }
+
+    setup_windows_sep()
+    assert_tails(paths)
+  end)
+
+  describe("handles linux paths", function()
+    local paths = {
+      [[/home/usuario/documents/archivo.txt]],
+      [[/var/www/html/index.html]],
+      [[/mnt/backup/backup_file.tar.gz]],
+    }
+
+    setup_unix_sep()
+    assert_tails(paths)
+  end)
+
+  describe("handles macos paths", function()
+    local paths = {
+      [[/Users/Usuario/Documents/archivo.txt]],
+      [[/Applications/App.app/Contents/MacOS/app_executable]],
+      [[/Volumes/ExternalDrive/Data/file.xlsx]],
+    }
+
+    setup_unix_sep()
+    assert_tails(paths)
+  end)
+end)