Change backtracking when packages conflict too much (#9843)

Background reading: #8157 Companion PR: astral-sh/pubgrub#36 Requires for test coverage: astral-sh/packse#230 When two packages A and B conflict, we have the option to choose a lower version of A, or a lower version of B. Currently, we determine this by the order we saw a package (assuming equal specificity of the requirement): If we saw A before B, we pin A until all versions of B are exhausted. This can lead to undesirable outcomes, from cases where it's just slow (sentry) to others cases without lower bounds where be backtrack to a very old version of B. This old version may fail to build (terminating the resolution), or it's a version so old that it doesn't depend on A (or the shared conflicting package) anymore - but also is too old for the user's application (fastapi). #8157 collects such cases, and the `wrong-backtracking` packse scenario contains a minimized example. We try to solve this by tracking which packages are "A"s, culprits, and "B"s, affected, and manually interfering with project selection and backtracking. Whenever a version we just chose is rejected, we give the current package a counter for being affected, and the package it conflicted with a counter for being a culprit. If a package accumulates more counts than a threshold, we reprioritize: Undecided after the culprits, after the affected, after packages that only have a single version (URLs, `==<version>`). We then ask pubgrub to backtrack just before the culprit. Due to the changed priorities, we now select package B, the affected, instead of package A, the culprit. To do this efficiently, we ask pubgrub for the incompatibility that caused backtracking, or just the last version to be discarded (due to its dependencies). For backtracking, we use the last incompatibility from unit propagation as a heuristic. When a version is discarded because one of its dependencies conflicts with the partial solution, the incompatibility tells us the package in the partial solution that conflicted. We only backtrack once per package, on the first time it passes the threshold. This prevents backtracking loops in which we make the same decisions over and over again. But we also changed the priority, so that we shouldn't take the same path even after the one time we backtrack (it would defeat the purpose of this change). There are some parameters that can be tweaked: Currently, the threshold is set to 5, which feels not too eager with so me of the conflicts that we want to tolerate but also changes strategies quickly. The relative order of the new priorities can also be changed, as for each (A, B) pair the priority of B is afterwards lower than that for A. Currently, culprits capture conflict for the whole package, but we could limit that to a specific version. We could discard conflict counters after backtracking instead of keeping them eternally as we do now. Note that we're always taking about pairs (A, B), but in practice we track individual packages, not pairs. A case that we wouldn't capture is when B is only introduced to the dependency graph after A, but I think that would require cyclical dependency for A and B to conflict? There may also be cases where looking at the last incompatibility is insufficient. Another example that we can't repair with prioritization is urllib3/boto3/botocore: We actually have to check all the newer versions of boto3 and botocore to identify the version that allows with the older urllib3, no shortcuts allowed. ``` urllib3<1.25.4 boto3 ``` All examples I tested were cases with two packages where we only had to switch the order, so I've abstracted them into a single packse case. This PR changes the resolution for certain paths, and there is the risk for regressions. Fixes #8157 --- All tested examples improved. Input fastapi: ```text starlette<=0.36.0 fastapi<=0.115.2 ``` ``` # BEFORE $ uv pip --no-progress compile -p 3.11 --exclude-newer 2024-10-01 --no-annotate debug/fastapi.txt annotated-types==0.7.0 anyio==4.6.0 fastapi==0.1.17 idna==3.10 pydantic==2.9.2 pydantic-core==2.23.4 sniffio==1.3.1 starlette==0.36.0 typing-extensions==4.12.2 # AFTER $ cargo run --profile fast-build --no-default-features pip compile -p 3.11 --no-progress --exclude-newer 2024-10-01 --no-annotate debug/fastapi.txt annotated-types==0.7.0 anyio==4.6.0 fastapi==0.109.1 idna==3.10 pydantic==2.9.2 pydantic-core==2.23.4 sniffio==1.3.1 starlette==0.35.1 typing-extensions==4.12.2 ``` Input xarray: ```text xarray[accel] ``` ``` # BEFORE $ uv pip --no-progress compile -p 3.11 --exclude-newer 2024-10-01 --no-annotate debug/xarray-accel.txt bottleneck==1.4.0 flox==0.9.13 llvmlite==0.36.0 numba==0.53.1 numbagg==0.8.2 numpy==2.1.1 numpy-groupies==0.11.2 opt-einsum==3.4.0 packaging==24.1 pandas==2.2.3 python-dateutil==2.9.0.post0 pytz==2024.2 scipy==1.14.1 setuptools==75.1.0 six==1.16.0 toolz==0.12.1 tzdata==2024.2 xarray==2024.9.0 # AFTER $ cargo run --profile fast-build --no-default-features pip compile -p 3.11 --no-progress --exclude-newer 2024-10-01 --no-annotate debug/xarray-accel.txt bottleneck==1.4.0 flox==0.9.13 llvmlite==0.43.0 numba==0.60.0 numbagg==0.8.2 numpy==2.0.2 numpy-groupies==0.11.2 opt-einsum==3.4.0 packaging==24.1 pandas==2.2.3 python-dateutil==2.9.0.post0 pytz==2024.2 scipy==1.14.1 six==1.16.0 toolz==0.12.1 tzdata==2024.2 xarray==2024.9.0 ``` Input sentry: The resolution is identical, but arrived at much faster: main tries 69 versions (sentry-kafka-schemas: 63), PR tries 12 versions (sentry-kafka-schemas: 6; 5 times conflicting, then once the right version). ```text python-rapidjson<=1.20,>=1.4 sentry-kafka-schemas<=0.1.113,>=0.1.50 ``` ``` # BEFORE $ uv pip --no-progress compile -p 3.11 --exclude-newer 2024-10-01 --no-annotate debug/sentry.txt fastjsonschema==2.20.0 msgpack==1.1.0 python-rapidjson==1.8 pyyaml==6.0.2 sentry-kafka-schemas==0.1.111 typing-extensions==4.12.2 # AFTER $ cargo run --profile fast-build --no-default-features pip compile -p 3.11 --no-progress --exclude-newer 2024-10-01 --no-annotate debug/sentry.txt fastjsonschema==2.20.0 msgpack==1.1.0 python-rapidjson==1.8 pyyaml==6.0.2 sentry-kafka-schemas==0.1.111 typing-extensions==4.12.2 ``` Input apache-beam ```text # Run on Python 3.10 dill<0.3.9,>=0.2.2 apache-beam<=2.49.0 ``` ``` # BEFORE $ uv pip --no-progress compile -p 3.10 --exclude-newer 2024-10-01 --no-annotate debug/apache-beam.txt × Failed to download and build `apache-beam==2.0.0` ╰─▶ Build backend failed to determine requirements with `build_wheel()` (exit status: 1) # AFTER $ cargo run --profile fast-build --no-default-features pip compile -p 3.10 --no-progress --exclude-newer 2024-10-01 --no-annotate debug/apache-beam.txt apache-beam==2.49.0 certifi==2024.8.30 charset-normalizer==3.3.2 cloudpickle==2.2.1 crcmod==1.7 dill==0.3.1.1 dnspython==2.6.1 docopt==0.6.2 fastavro==1.9.7 fasteners==0.19 grpcio==1.66.2 hdfs==2.7.3 httplib2==0.22.0 idna==3.10 numpy==1.24.4 objsize==0.6.1 orjson==3.10.7 proto-plus==1.24.0 protobuf==4.23.4 pyarrow==11.0.0 pydot==1.4.2 pymongo==4.10.0 pyparsing==3.1.4 python-dateutil==2.9.0.post0 pytz==2024.2 regex==2024.9.11 requests==2.32.3 six==1.16.0 typing-extensions==4.12.2 urllib3==2.2.3 zstandard==0.23.0 ```
astral-sh · Dec 16, 2024 · 431ddc1 · 431ddc1
1 parent 2b61a67
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diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
@@ -130,7 +130,7 @@ petgraph = { version = "0.6.5" }
 platform-info = { version = "2.0.3" }
 proc-macro2 = { version = "1.0.86" }
 procfs = { version = "0.17.0", default-features = false, features = ["flate2"] }
-pubgrub = { git = "https://github.com/astral-sh/pubgrub", rev = "57832d0588fbb7aab824813481104761dc1c7740" }
+pubgrub = { git = "https://github.com/astral-sh/pubgrub", rev = "05e8d12cea8d72c6d2d017900e478d0abd28fef4" }
 quote = { version = "1.0.37" }
 rayon = { version = "1.10.0" }
 reflink-copy = { version = "0.1.19" }
@@ -175,7 +175,7 @@ unicode-width = { version = "0.1.13" }
 unscanny = { version = "0.1.0" }
 url = { version = "2.5.2", features = ["serde"] }
 urlencoding = { version = "2.1.3" }
-version-ranges = { git = "https://github.com/astral-sh/pubgrub", rev = "57832d0588fbb7aab824813481104761dc1c7740" }
+version-ranges = { git = "https://github.com/astral-sh/pubgrub", rev = "05e8d12cea8d72c6d2d017900e478d0abd28fef4" }
 walkdir = { version = "2.5.0" }
 which = { version = "7.0.0", features = ["regex"] }
 windows-registry = { version = "0.3.0" }

diff --git a/crates/uv-resolver/src/dependency_provider.rs b/crates/uv-resolver/src/dependency_provider.rs
@@ -1,6 +1,6 @@
 use std::convert::Infallible;
 
-use pubgrub::{Dependencies, DependencyProvider, Range};
+use pubgrub::{Dependencies, DependencyProvider, PackageResolutionStatistics, Range};
 
 use uv_pep440::Version;
 
@@ -17,13 +17,17 @@ impl DependencyProvider for UvDependencyProvider {
     type V = Version;
     type VS = Range<Version>;
     type M = UnavailableReason;
+    type Priority = Option<PubGrubPriority>;
+    type Err = Infallible;
 
-    fn prioritize(&self, _package: &Self::P, _range: &Self::VS) -> Self::Priority {
+    fn prioritize(
+        &self,
+        _package: &Self::P,
+        _range: &Self::VS,
+        _stats: &PackageResolutionStatistics,
+    ) -> Self::Priority {
         unimplemented!()
     }
-    type Priority = Option<PubGrubPriority>;
-
-    type Err = Infallible;
 
     fn choose_version(
         &self,

diff --git a/crates/uv-resolver/src/pubgrub/priority.rs b/crates/uv-resolver/src/pubgrub/priority.rs
@@ -1,7 +1,7 @@
-use std::cmp::Reverse;
-
 use pubgrub::Range;
 use rustc_hash::FxHashMap;
+use std::cmp::Reverse;
+use std::collections::hash_map::OccupiedEntry;
 
 use crate::fork_urls::ForkUrls;
 use uv_normalize::PackageName;
@@ -40,19 +40,22 @@ impl PubGrubPriorities {
         match self.0.entry(name.clone()) {
             std::collections::hash_map::Entry::Occupied(mut entry) => {
                 // Preserve the original index.
-                let index = match entry.get() {
-                    PubGrubPriority::Unspecified(Reverse(index)) => *index,
-                    PubGrubPriority::Singleton(Reverse(index)) => *index,
-                    PubGrubPriority::DirectUrl(Reverse(index)) => *index,
-                    PubGrubPriority::Root => next,
-                };
+                let index = Self::get_index(&entry).unwrap_or(next);
 
                 // Compute the priority.
                 let priority = if urls.get(name).is_some() {
                     PubGrubPriority::DirectUrl(Reverse(index))
                 } else if version.as_singleton().is_some() {
                     PubGrubPriority::Singleton(Reverse(index))
                 } else {
+                    // Keep the conflict-causing packages to avoid loops where we seesaw between
+                    // `Unspecified` and `Conflict*`.
+                    if matches!(
+                        entry.get(),
+                        PubGrubPriority::ConflictEarly(_) | PubGrubPriority::ConflictLate(_)
+                    ) {
+                        return;
+                    }
                     PubGrubPriority::Unspecified(Reverse(index))
                 };
 
@@ -77,6 +80,17 @@ impl PubGrubPriorities {
         }
     }
 
+    fn get_index(entry: &OccupiedEntry<PackageName, PubGrubPriority>) -> Option<usize> {
+        match entry.get() {
+            PubGrubPriority::ConflictLate(Reverse(index))
+            | PubGrubPriority::Unspecified(Reverse(index))
+            | PubGrubPriority::ConflictEarly(Reverse(index))
+            | PubGrubPriority::Singleton(Reverse(index))
+            | PubGrubPriority::DirectUrl(Reverse(index)) => Some(*index),
+            PubGrubPriority::Root => None,
+        }
+    }
+
     /// Return the [`PubGrubPriority`] of the given package, if it exists.
     pub(crate) fn get(&self, package: &PubGrubPackage) -> Option<PubGrubPriority> {
         match &**package {
@@ -88,6 +102,79 @@ impl PubGrubPriorities {
             PubGrubPackageInner::Package { name, .. } => self.0.get(name).copied(),
         }
     }
+
+    /// Mark a package as prioritized by setting it to [`PubGrubPriority::ConflictEarly`], if it
+    /// doesn't have a higher priority already.
+    ///
+    /// Returns whether the priority was changed, i.e., it's the first time we hit this condition
+    /// for the package.
+    pub(crate) fn mark_conflict_early(&mut self, package: &PubGrubPackage) -> bool {
+        let next = self.0.len();
+        let Some(name) = package.name_no_root() else {
+            // Not a correctness bug
+            if cfg!(debug_assertions) {
+                panic!("URL packages must not be involved in conflict handling")
+            } else {
+                return false;
+            }
+        };
+        match self.0.entry(name.clone()) {
+            std::collections::hash_map::Entry::Occupied(mut entry) => {
+                if matches!(
+                    entry.get(),
+                    PubGrubPriority::ConflictEarly(_) | PubGrubPriority::Singleton(_)
+                ) {
+                    // Already in the right category
+                    return false;
+                };
+                let index = Self::get_index(&entry).unwrap_or(next);
+                entry.insert(PubGrubPriority::ConflictEarly(Reverse(index)));
+                true
+            }
+            std::collections::hash_map::Entry::Vacant(entry) => {
+                entry.insert(PubGrubPriority::ConflictEarly(Reverse(next)));
+                true
+            }
+        }
+    }
+
+    /// Mark a package as prioritized by setting it to [`PubGrubPriority::ConflictLate`], if it
+    /// doesn't have a higher priority already.
+    ///
+    /// Returns whether the priority was changed, i.e., it's the first time this package was
+    /// marked as conflicting above the threshold.
+    pub(crate) fn mark_conflict_late(&mut self, package: &PubGrubPackage) -> bool {
+        let next = self.0.len();
+        let Some(name) = package.name_no_root() else {
+            // Not a correctness bug
+            if cfg!(debug_assertions) {
+                panic!("URL packages must not be involved in conflict handling")
+            } else {
+                return false;
+            }
+        };
+        match self.0.entry(name.clone()) {
+            std::collections::hash_map::Entry::Occupied(mut entry) => {
+                // The ConflictEarly` match avoids infinite loops.
+                if matches!(
+                    entry.get(),
+                    PubGrubPriority::ConflictLate(_)
+                        | PubGrubPriority::ConflictEarly(_)
+                        | PubGrubPriority::Singleton(_)
+                ) {
+                    // Already in the right category
+                    return false;
+                };
+                let index = Self::get_index(&entry).unwrap_or(next);
+                entry.insert(PubGrubPriority::ConflictLate(Reverse(index)));
+                true
+            }
+            std::collections::hash_map::Entry::Vacant(entry) => {
+                entry.insert(PubGrubPriority::ConflictLate(Reverse(next)));
+                true
+            }
+        }
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
@@ -101,6 +188,15 @@ pub(crate) enum PubGrubPriority {
     /// in the dependency graph.
     Unspecified(Reverse<usize>),
 
+    /// Selected version of this package were often the culprit of rejecting another package, so
+    /// it's deprioritized behind `ConflictEarly`. It's still the higher than `Unspecified` to
+    /// conflict before selecting unrelated packages.
+    ConflictLate(Reverse<usize>),
+
+    /// Selected version of this package were often rejected, so it's prioritized over
+    /// `ConflictLate`.
+    ConflictEarly(Reverse<usize>),
+
     /// The version range is constrained to a single version (e.g., with the `==` operator).
     Singleton(Reverse<usize>),