fix(pickers): improve CRLF line splitting support for windows (#3127)

* 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

* fix: handle cross platform line splits

lua/tests/automated/utils_spec.lua

@@ -307,3 +307,87 @@ describe("transform_path", function()
     end, new_relpath "doc/mydoc.md", new_relpath "d/mydoc.md")
   end)
 end)
+
+describe("path_tail", function()
+  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
+
+  if jit and jit.os:lower() == "windows" then
+    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]],
+      }
+
+      assert_tails(paths)
+    end)
+  elseif jit and jit.os:lower() == "linux" then
+    describe("handles linux paths", function()
+      local paths = {
+        [[/home/usuario/documents/archivo.txt]],
+        [[/var/www/html/index.html]],
+        [[/mnt/backup/backup_file.tar.gz]],
+      }
+
+      assert_tails(paths)
+    end)
+  elseif jit and jit.os:lower() == "osx" then
+    describe("handles macos paths", function()
+      local paths = {
+        [[/Users/Usuario/Documents/archivo.txt]],
+        [[/Applications/App.app/Contents/MacOS/app_executable]],
+        [[/Volumes/ExternalDrive/Data/file.xlsx]],
+      }
+
+      assert_tails(paths)
+    end)
+  end
+end)
+
+describe("split_lines", function()
+  local expect = {
+    "",
+    "",
+    "line3 of the file",
+    "",
+    "line5 of the file",
+    "",
+    "",
+    "line8 of the file, last line of file",
+    "",
+  }
+
+  local function get_fake_file(line_ending)
+    return table.concat(expect, line_ending)
+  end
+
+  local newline_file = get_fake_file "\n"
+  local carriage_newline_file = get_fake_file "\r\n"
+
+  if utils.iswin then
+    describe("handles files on Windows", function()
+      it("reads file with newline only", function()
+        assert.are.same(expect, utils.split_lines(newline_file))
+      end)
+      it("reads file with carriage return and newline", function()
+        assert.are.same(expect, utils.split_lines(carriage_newline_file))
+      end)
+    end)
+  else
+    describe("handles files on non Windows environment", function()
+      it("reads file with newline only", function()
+        assert.are.same(expect, utils.split_lines(newline_file))
+      end)
+    end)
+  end
+end)