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## Summary This PR rewrites the `MarkerTree` type to use algebraic decision diagrams (ADD). This has many benefits: - The diagram is canonical for a given marker function. It is impossible to create two functionally equivalent marker trees that don't refer to the same underlying ADD. This also means that any trivially true or unsatisfiable markers are represented by the same constants. - The diagram can handle complex operations (conjunction/disjunction) in polynomial time, as well as constant-time negation. - The diagram can be converted to a simplified DNF form for user-facing output. The new representation gives us a lot more confidence in our marker operations and simplification, which is proving to be very important (see https://github.com/astral-sh/uv/pull/5733 and https://github.com/astral-sh/uv/pull/5163). Unfortunately, it is not easy to split this PR into multiple commits because it is a large rewrite of the `marker` module. I'd suggest reading through the `marker/algebra.rs`, `marker/simplify.rs`, and `marker/tree.rs` files for the new implementation, as well as the updated snapshots to verify how the new simplification rules work in practice. However, a few other things were changed: - [We now use release-only comparisons for `python_full_version`, where we previously only did for `python_version`](https://github.com/astral-sh/uv/blob/ibraheem/canonical-markers/crates/pep508-rs/src/marker/algebra.rs#L522). I'm unsure how marker operations should work in the presence of pre-release versions if we decide that this is incorrect. - [Meaningless marker expressions are now ignored](https://github.com/astral-sh/uv/blob/ibraheem/canonical-markers/crates/pep508-rs/src/marker/parse.rs#L502). This means that a marker such as `'x' == 'x'` will always evaluate to `true` (as if the expression did not exist), whereas we previously treated this as always `false`. It's negation however, remains `false`. - [Unsatisfiable markers are written as `python_version < '0'`](https://github.com/astral-sh/uv/blob/ibraheem/canonical-markers/crates/pep508-rs/src/marker/tree.rs#L1329). - The `PubGrubSpecifier` type has been moved to the new `uv-pubgrub` crate, shared by `pep508-rs` and `uv-resolver`. `pep508-rs` also depends on the `pubgrub` crate for the `Range` type, we probably want to move `pubgrub::Range` into a separate crate to break this, but I don't think that should block this PR (cc @konstin). There is still some remaining work here that I decided to leave for now for the sake of unblocking some of the related work on the resolver. - We still use `Option<MarkerTree>` throughout uv, which is unnecessary now that `MarkerTree::TRUE` is canonical. - The `MarkerTree` type is now interned globally and can potentially implement `Copy`. However, it's unclear if we want to add more information to marker trees that would make it `!Copy`. For example, we may wish to attach extra and requires-python environment information to avoid simplifying after construction. - We don't currently combine `python_full_version` and `python_version` markers. - I also have not spent too much time investigating performance and there is probably some low-hanging fruit. Many of the test cases I did run actually saw large performance improvements due to the markers being simplified internally, reducing the stress on the old `normalize` routine, especially for the extremely large markers seen in `transformers` and other projects. Resolves https://github.com/astral-sh/uv/issues/5660, https://github.com/astral-sh/uv/issues/5179. |
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| Readme.md | ||
Dependency specifiers (PEP 508) in Rust
A library for python dependency specifiers, better known as PEP 508.
Usage
In Rust
use std::str::FromStr;
use pep508_rs::Requirement;
let marker = r#"requests [security,tests] >= 2.8.1, == 2.8.* ; python_version > "3.8""#;
let dependency_specification = Requirement::from_str(marker).unwrap();
assert_eq!(dependency_specification.name, "requests");
assert_eq!(dependency_specification.extras, Some(vec!["security".to_string(), "tests".to_string()]));
In Python
from pep508_rs import Requirement
requests = Requirement(
'requests [security,tests] >= 2.8.1, == 2.8.* ; python_version > "3.8"'
)
assert requests.name == "requests"
assert requests.extras == ["security", "tests"]
assert [str(i) for i in requests.version_or_url] == [">= 2.8.1", "== 2.8.*"]
Python bindings are built with maturin, but you can also use the
normal pip install .
Version and VersionSpecifier from pep440_rs are
reexported to avoid type mismatches.
Markers
Markers allow you to install dependencies only in specific environments (python version, operating
system, architecture, etc.) or when a specific feature is activated. E.g. you can say
importlib-metadata ; python_version < "3.8" or itsdangerous (>=1.1.0) ; extra == 'security'.
Unfortunately, the marker grammar has some oversights (e.g.
https://github.com/pypa/packaging.python.org/pull/1181) and the design of comparisons (PEP 440
comparisons with lexicographic fallback) leads to confusing outcomes. This implementation tries to
carefully validate everything and emit warnings whenever bogus comparisons with unintended semantics
are made.
In python, warnings are by default sent to the normal python logging infrastructure:
from pep508_rs import Requirement, MarkerEnvironment
env = MarkerEnvironment.current()
assert not Requirement("numpy; extra == 'science'").evaluate_markers(env, [])
assert Requirement("numpy; extra == 'science'").evaluate_markers(env, ["science"])
assert not Requirement(
"numpy; extra == 'science' and extra == 'arrays'"
).evaluate_markers(env, ["science"])
assert Requirement(
"numpy; extra == 'science' or extra == 'arrays'"
).evaluate_markers(env, ["science"])
from pep508_rs import Requirement, MarkerEnvironment
env = MarkerEnvironment.current()
Requirement("numpy; python_version >= '3.9.'").evaluate_markers(env, [])
# This will log:
# "Expected PEP 440 version to compare with python_version, found '3.9.', "
# "evaluating to false: Version `3.9.` doesn't match PEP 440 rules"