docs: Rewrite Handling Paths chapter (pathlib vs utils) (#6116)

## Description

Updates the docs chapter "Handling Paths" describing how to modernise
old code and intentionally includes historical details. Examples should
further guide contributors while refactoring. 

Also moved the guide from the contribution guide into the dev docs.

CONTRIBUTING.rst

@@ -286,31 +286,6 @@ according to the specifications required by the project.
 Similarly, run ``poe format-docs`` and ``poe lint-docs`` to ensure consistent
 documentation formatting and check for any issues.
 
-Handling Paths
-~~~~~~~~~~~~~~
-
-A great deal of convention deals with the handling of **paths**. Paths are
-stored internally—in the database, for instance—as byte strings (i.e., ``bytes``
-instead of ``str`` in Python 3). This is because POSIX operating systems’ path
-names are only reliably usable as byte strings—operating systems typically
-recommend but do not require that filenames use a given encoding, so violations
-of any reported encoding are inevitable. On Windows, the strings are always
-encoded with UTF-8; on Unix, the encoding is controlled by the filesystem. Here
-are some guidelines to follow:
-
-- If you have a Unicode path or you’re not sure whether something is Unicode or
-  not, pass it through ``bytestring_path`` function in the ``beets.util`` module
-  to convert it to bytes.
-- Pass every path name through the ``syspath`` function (also in ``beets.util``)
-  before sending it to any *operating system* file operation (``open``, for
-  example). This is necessary to use long filenames (which, maddeningly, must be
-  Unicode) on Windows. This allows us to consistently store bytes in the
-  database but use the native encoding rule on both POSIX and Windows.
-- Similarly, the ``displayable_path`` utility function converts bytestring paths
-  to a Unicode string for displaying to the user. Every time you want to print
-  out a string to the terminal or log it with the ``logging`` module, feed it
-  through this function.
-
 Editor Settings
 ~~~~~~~~~~~~~~~
 

docs/changelog.rst

@@ -26,6 +26,10 @@ For packagers:
 
 Other changes:
 
+- The documentation chapter :doc:`dev/paths` has been moved to the "For
+  Developers" section and revised to reflect current best practices (pathlib
+  usage).
+
 2.5.1 (October 14, 2025)
 ------------------------
 

docs/dev/index.rst

@@ -18,6 +18,7 @@ configuration files, respectively.
 
     plugins/index
     library
+    paths
     importer
     cli
     ../api/index

docs/dev/paths.rst

@@ -0,0 +1,64 @@
+Handling Paths
+==============
+
+``pathlib`` provides a clean, cross-platform API for working with filesystem
+paths.
+
+Use the ``.filepath`` property on ``Item`` and ``Album`` library objects to
+access paths as ``pathlib.Path`` objects. This produces a readable, native
+representation suitable for printing, logging, or further processing.
+
+Normalize paths using ``Path(...).expanduser().resolve()``, which expands ``~``
+and resolves symlinks.
+
+Cross-platform differences—such as path separators, Unicode handling, and
+long-path support (Windows) are automatically managed by ``pathlib``.
+
+When storing paths in the database, however, convert them to bytes with
+``bytestring_path()``. Paths in Beets are currently stored as bytes, although
+there are plans to eventually store ``pathlib.Path`` objects directly. To access
+media file paths in their stored form, use the ``.path`` property on ``Item``
+and ``Album``.
+
+Legacy utilities
+----------------
+
+Historically, Beets used custom utilities to ensure consistent behavior across
+Linux, macOS, and Windows before ``pathlib`` became reliable:
+
+- ``syspath()``: worked around Windows Unicode and long-path limitations by
+  converting to a system-safe string (adding the ``\\?\`` prefix where needed).
+- ``normpath()``: normalized slashes and removed ``./`` or ``..`` parts but did
+  not expand ``~``.
+- ``bytestring_path()``: converted paths to bytes for database storage (still
+  used for that purpose today).
+- ``displayable_path()``: converted byte paths to Unicode for display or
+  logging.
+
+These functions remain safe to use in legacy code, but new code should rely
+solely on ``pathlib.Path``.
+
+Examples
+--------
+
+Old style
+
+.. code-block:: python
+
+    displayable_path(item.path)
+    normpath("~/Music/../Artist")
+    syspath(path)
+
+New style
+
+.. code-block:: python
+
+    item.filepath
+    Path("~/Music/../Artist").expanduser().resolve()
+    Path(path)
+
+When storing paths in the database
+
+.. code-block:: python
+
+    path_bytes = bytestring_path(Path("/some/path/to/file.mp3"))