Lockfile-normalized marker representation #5179
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konstin
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ibraheemdev
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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 #5733 and #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 #5660, #5179.
zanieb
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Aug 9, 2024
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 #5733 and #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 #5660, #5179.
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We now markers in a simplified DNF form. Our simplification is not perfect, but it seems to work well in practice. See #5992 for whether we should write as CNF in some cases, but for now I think we're in a good place. |
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Awesome. |
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We need to decide on which normalization we want for markers in the lockfile, and implement the algorithm that performs this normalization. For example, #5163 introduces:
This marker can be (completely) collapsed, in the current form it's not readable.
Since the marker representation changes the lockfile, we need a stable representation.
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