Add doc on picking resolvers

Also bump cache up: on `bench` the `basic` resolver high water marks
as:

- 40MB with no cache, averaging 455µs/line
- 40.7MB with a 200 entries s3fifo, averaging 324µs/line
- 42.4MB with a 2000 entries s3fifo, averaging 191µs/line
- 44.2MB with a 5000 entries s3fifo, averaging 155µs/line
- 47.2MB with a 10000 entries s3fifo, averaging 134µs/line
- 53MB with a 2000 entries s3fifo, averaging 123µs/line

Either 2000 or 5000 seem like pretty good defaults, the gains taper
afterwards as memory use increases sharply. Bump to 2000 to stay on
the conservative side.

README.rst

@@ -30,17 +30,20 @@ Just add ``ua-parser`` to your project's dependencies, or run
 
 to install in the current environment.
 
-Installing `google-re2 <https://pypi.org/project/google-re2/>`_ is
-*strongly* recommended as it leads to *significantly* better
-performances. This can be done directly via the ``re2`` optional
-dependency:
+Installing `ua-parser-rs <https://pypi.org/project/ua-parser-rs>`_ or
+`google-re2 <https://pypi.org/project/google-re2/>`_ is *strongly*
+recommended as they yield *significantly* better performances. This
+can be done directly via the ``regex`` and ``re2`` optional
+dependencies respectively:
 
 .. code-block:: sh
 
+    $ pip install 'ua_parser[regex]'
     $ pip install 'ua_parser[re2]'
 
-If ``re2`` is available, ``ua-parser`` will simply use it by default
-instead of the pure-python resolver.
+If either dependency is already available (e.g. because the software
+makes use of re2 for other reasons) ``ua-parser`` will use the
+corresponding resolver automatically.
 
 Quick Start
 -----------

doc/api.rst

@@ -75,6 +75,19 @@ from user agent strings.
 
    .. warning:: Only available if |re2|_ is installed.
 
+.. class::ua_parser.regex.Resolver(Matchers)
+
+   An advanced resolver based on |regex|_ and a bespoke implementation
+   of regex prefiltering, by the sibling project `ua-rust
+   <https://github.com/ua-parser/uap-rust`_.
+
+   Sufficiently fast that a cache may not be necessary, and may even
+   be detrimental at smaller cache sizes
+
+   .. warning:: Only available if `ua-parser-rs
+                <https://pypi.org/project/ua-parser-rs/`>_ is
+                installed.
+
 Eager Matchers
 ''''''''''''''
 

doc/guides.rst

@@ -129,6 +129,103 @@ from here on::
    :class:`~ua_parser.caching.Local`, which is also caching-related,
    and serves to use thread-local caches rather than a shared cache.
 
+Builtin Resolvers
+=================
+
+.. list-table::
+   :header-rows: 1
+   :stub-columns: 1
+
+   * -
+     - speed
+     - portability
+     - memory use
+     - safety
+   * - ``regex``
+     - great
+     - good
+     - bad
+     - great
+   * - ``re2``
+     - good
+     - bad
+     - good
+     - good
+   * - ``basic``
+     - terrible
+     - great
+     - great
+     - great
+
+``regex``
+---------
+
+The ``regex`` resolver is a bespoke effort as part of the `uap-rust
+<https://github.com/ua-parser/uap-rust>`_ sibling project, built on
+`rust-regex <https://github.com/rust-lang/regex>`_ and `a bespoke
+regex-prefiltering implementation
+<https://github.com/ua-parser/uap-rust/tree/main/regex-filtered>`_,
+it:
+
+- Is the fastest available resolver, usually edging out ``re2`` by a
+  significant margin (when that is even available).
+- Is fully controlled by the project, and thus can be built for all
+  interpreters and platforms supported by pyo3 (currently: cpython,
+  pypy, and graalpy, on linux, macos and linux, intel and arm). It is
+  also built as a cpython abi3 wheel and should thus suffer from no
+  compatibility issues with new release.
+- Built entirely out of safe rust code, its safety risks are entirely
+  in ``regex`` and ``pyo3``.
+- Its biggest drawback is that it is a lot more memory intensive than
+  the other resolvers, because ``regex`` tends to trade memory for
+  speed (~155MB high water mark on a real-world dataset).
+
+If available, it is the default resolver, without a cache.
+
+``re2``
+-------
+
+The ``re2`` resolver is built atop the widely used `google-re2
+<https://github.com/google/re2>`_ via its built-in Python bindings.
+It:
+
+- Is extremely fast, though around 80% slower than ``regex`` on
+  real-world data.
+- Is only compatible with CPython, and uses pure API wheels, so needs
+  a different release for each cpython version, for each OS, for each
+  architecture.
+- Is built entirely in C++, but by experienced Google developers.
+- Is more memory intensive than the pure-python ``basic`` resolver,
+  but quite slim all things considered (~55MB high water mark on a
+  real-world dataset).
+
+If available, it is the second-preferred resolver, without a cache.
+
+``basic``
+---------
+
+The ``basic`` resolver is a naive linear traversal of all rules, using
+the standard library's ``re``. It:
+
+- Is *extremely* slow, about 10x slower than ``re2`` in cpython, and
+  pypy and graal's regex implementations do *not* like the workload
+  and behind cpython by a factor of 3~4.
+- Has perfect compatibility, with the caveat above, by virtue of being
+  built entirely out of standard library code.
+- Is basically as safe as Python software can be by virtue of being
+  just Python, with the native code being the standard library's.
+- Is the slimmest resolver at about 40MB.
+
+This is caveated by a hard requirement to use caches which makes it
+workably faster on real-world datasets (if still nowhere near
+*uncached* ``re2`` or ``regex``) but increases its memory requirement
+significantly e.g. using "sieve" and a cache size of 20000 on a
+real-world dataset, it is about 4x slower than ``re2`` for about the
+same memory requirements.
+
+It is the fallback and least preferred resolver, with a medium
+(currently 2000 entries) cache by default.
+
 Writing Custom Resolvers
 ========================
 

doc/installation.rst

@@ -35,3 +35,9 @@ if installed, but can also be installed via and alongside ua-parser:
    $ pip install 'ua-parser[yaml]'
    $ pip install 'ua-parser[regex,yaml]'
 
+``yaml`` simply enables the ability to :func:`load yaml rulesets
+<ua_parser.loaders.load_yaml>`.
+
+The other two dependencies enable more efficient resolvers. By
+default, ``ua-parser`` will select the fastest resolver it finds out
+of the available set. For more, see :ref:`builtin resolvers`.

src/ua_parser/__init__.py

@@ -72,7 +72,7 @@
         (
             RegexResolver,
             Re2Resolver,
-            lambda m: CachingResolver(BasicResolver(m), Cache(200)),
+            lambda m: CachingResolver(BasicResolver(m), Cache(2000)),
         ),
     )
 )