feat!: allocation free errors

examples/caching_dependency_provider.rs

@@ -1,7 +1,6 @@
 // SPDX-License-Identifier: MPL-2.0
 
 use std::cell::RefCell;
-use std::error::Error;
 
 use pubgrub::package::Package;
 use pubgrub::range::Range;
@@ -37,7 +36,7 @@ impl<P: Package, VS: VersionSet, DP: DependencyProvider<P, VS>> DependencyProvid
         &self,
         package: &P,
         version: &VS::V,
-    ) -> Result<Dependencies<P, VS>, Box<dyn Error + Send + Sync>> {
+    ) -> Result<Dependencies<P, VS>, DP::Err> {
         let mut cache = self.cached_dependencies.borrow_mut();
         match cache.get_dependencies(package, version) {
             Ok(Dependencies::Unknown) => {
@@ -55,16 +54,12 @@ impl<P: Package, VS: VersionSet, DP: DependencyProvider<P, VS>> DependencyProvid
                     error @ Err(_) => error,
                 }
             }
-            dependencies @ Ok(_) => dependencies,
-            error @ Err(_) => error,
+            Ok(dependencies) => Ok(dependencies),
+            Err(_) => unreachable!(),
         }
     }
 
-    fn choose_version(
-        &self,
-        package: &P,
-        range: &VS,
-    ) -> Result<Option<VS::V>, Box<dyn Error + Send + Sync>> {
+    fn choose_version(&self, package: &P, range: &VS) -> Result<Option<VS::V>, DP::Err> {
         self.remote_dependencies.choose_version(package, range)
     }
 
@@ -73,6 +68,8 @@ impl<P: Package, VS: VersionSet, DP: DependencyProvider<P, VS>> DependencyProvid
     fn prioritize(&self, package: &P, range: &VS) -> Self::Priority {
         self.remote_dependencies.prioritize(package, range)
     }
+
+    type Err = DP::Err;
 }
 
 fn main() {

src/error.rs

@@ -10,7 +10,7 @@ use crate::version_set::VersionSet;
 
 /// Errors that may occur while solving dependencies.
 #[derive(Error, Debug)]
-pub enum PubGrubError<P: Package, VS: VersionSet> {
+pub enum PubGrubError<P: Package, VS: VersionSet, E: std::error::Error> {
     /// There is no solution for this set of dependencies.
     #[error("No solution")]
     NoSolution(DerivationTree<P, VS>),
@@ -27,7 +27,7 @@ pub enum PubGrubError<P: Package, VS: VersionSet> {
         version: VS::V,
         /// Error raised by the implementer of
         /// [DependencyProvider](crate::solver::DependencyProvider).
-        source: Box<dyn std::error::Error + Send + Sync>,
+        source: E,
     },
 
     /// Error arising when the implementer of
@@ -48,12 +48,12 @@ pub enum PubGrubError<P: Package, VS: VersionSet> {
     /// returned an error in the method
     /// [choose_version](crate::solver::DependencyProvider::choose_version).
     #[error("Decision making failed")]
-    ErrorChoosingPackageVersion(Box<dyn std::error::Error + Send + Sync>),
+    ErrorChoosingPackageVersion(E),
 
     /// Error arising when the implementer of [DependencyProvider](crate::solver::DependencyProvider)
     /// returned an error in the method [should_cancel](crate::solver::DependencyProvider::should_cancel).
     #[error("We should cancel")]
-    ErrorInShouldCancel(Box<dyn std::error::Error + Send + Sync>),
+    ErrorInShouldCancel(E),
 
     /// Something unexpected happened.
     #[error("{0}")]

src/internal/core.rs

@@ -4,6 +4,7 @@
 //! to write a functional PubGrub algorithm.
 
 use std::collections::HashSet as Set;
+use std::error::Error;
 
 use crate::error::PubGrubError;
 use crate::internal::arena::Arena;
@@ -92,7 +93,7 @@ impl<P: Package, VS: VersionSet, Priority: Ord + Clone> State<P, VS, Priority> {
 
     /// Unit propagation is the core mechanism of the solving algorithm.
     /// CF <https://github.com/dart-lang/pub/blob/master/doc/solver.md#unit-propagation>
-    pub fn unit_propagation(&mut self, package: P) -> Result<(), PubGrubError<P, VS>> {
+    pub fn unit_propagation<E: Error>(&mut self, package: P) -> Result<(), PubGrubError<P, VS, E>> {
         self.unit_propagation_buffer.clear();
         self.unit_propagation_buffer.push(package);
         while let Some(current_package) = self.unit_propagation_buffer.pop() {
@@ -154,10 +155,11 @@ impl<P: Package, VS: VersionSet, Priority: Ord + Clone> State<P, VS, Priority> {
 
     /// Return the root cause and the backtracked model.
     /// CF <https://github.com/dart-lang/pub/blob/master/doc/solver.md#unit-propagation>
-    fn conflict_resolution(
+    #[allow(clippy::type_complexity)]
+    fn conflict_resolution<E: Error>(
         &mut self,
         incompatibility: IncompId<P, VS>,
-    ) -> Result<(P, IncompId<P, VS>), PubGrubError<P, VS>> {
+    ) -> Result<(P, IncompId<P, VS>), PubGrubError<P, VS, E>> {
         let mut current_incompat_id = incompatibility;
         let mut current_incompat_changed = false;
         loop {

src/lib.rs

@@ -83,13 +83,14 @@
 //! # use pubgrub::type_aliases::Map;
 //! # use std::error::Error;
 //! # use std::borrow::Borrow;
+//! # use std::convert::Infallible;
 //! #
 //! # struct MyDependencyProvider;
 //! #
 //! type SemVS = Range<SemanticVersion>;
 //!
 //! impl DependencyProvider<String, SemVS> for MyDependencyProvider {
-//!     fn choose_version(&self, package: &String, range: &SemVS) -> Result<Option<SemanticVersion>, Box<dyn Error + Send + Sync>> {
+//!     fn choose_version(&self, package: &String, range: &SemVS) -> Result<Option<SemanticVersion>, Infallible> {
 //!         unimplemented!()
 //!     }
 //!
@@ -102,9 +103,11 @@
 //!         &self,
 //!         package: &String,
 //!         version: &SemanticVersion,
-//!     ) -> Result<Dependencies<String, SemVS>, Box<dyn Error + Send + Sync>> {
+//!     ) -> Result<Dependencies<String, SemVS>, Infallible> {
 //!         unimplemented!()
 //!     }
+//!
+//!     type Err = Infallible;
 //! }
 //! ```
 //!

src/solver.rs

@@ -41,14 +41,15 @@
 //! ## API
 //!
 //! ```
+//! # use std::convert::Infallible;
 //! # use pubgrub::solver::{resolve, OfflineDependencyProvider};
 //! # use pubgrub::version::NumberVersion;
 //! # use pubgrub::error::PubGrubError;
 //! # use pubgrub::range::Range;
 //! #
 //! # type NumVS = Range<NumberVersion>;
 //! #
-//! # fn try_main() -> Result<(), PubGrubError<&'static str, NumVS>> {
+//! # fn try_main() -> Result<(), PubGrubError<&'static str, NumVS, Infallible>> {
 //! #     let dependency_provider = OfflineDependencyProvider::<&str, NumVS>::new();
 //! #     let package = "root";
 //! #     let version = 1;
@@ -70,6 +71,7 @@
 
 use std::cmp::Reverse;
 use std::collections::{BTreeMap, BTreeSet as Set};
+use std::convert::Infallible;
 use std::error::Error;
 
 use crate::error::PubGrubError;
@@ -82,11 +84,12 @@ use log::{debug, info};
 
 /// Main function of the library.
 /// Finds a set of packages satisfying dependency bounds for a given package + version pair.
-pub fn resolve<P: Package, VS: VersionSet>(
-    dependency_provider: &impl DependencyProvider<P, VS>,
+#[allow(clippy::type_complexity)]
+pub fn resolve<P: Package, VS: VersionSet, DP: DependencyProvider<P, VS>>(
+    dependency_provider: &DP,
     package: P,
     version: impl Into<VS::V>,
-) -> Result<SelectedDependencies<P, VS::V>, PubGrubError<P, VS>> {
+) -> Result<SelectedDependencies<P, VS::V>, PubGrubError<P, VS, DP::Err>> {
     let mut state = State::init(package.clone(), version.into());
     let mut added_dependencies: Map<P, Set<VS::V>> = Map::default();
     let mut next = package;
@@ -133,7 +136,7 @@ pub fn resolve<P: Package, VS: VersionSet>(
         };
 
         if !term_intersection.contains(&v) {
-            return Err(PubGrubError::ErrorChoosingPackageVersion(
+            return Err(PubGrubError::Failure(
                 "choose_package_version picked an incompatible version".into(),
             ));
         }
@@ -240,29 +243,30 @@ pub trait DependencyProvider<P: Package, VS: VersionSet> {
     /// the fewest versions that match the outstanding constraint.
     type Priority: Ord + Clone;
 
+    /// The kind of error returned from these methods.
+    ///
+    /// Returning this signals that resolution should fail with this error.
+    type Err: Error;
+
     /// Once the resolver has found the highest `Priority` package from all potential valid
     /// packages, it needs to know what vertion of that package to use. The most common pattern
     /// is to select the largest vertion that the range contains.
-    fn choose_version(
-        &self,
-        package: &P,
-        range: &VS,
-    ) -> Result<Option<VS::V>, Box<dyn Error + Send + Sync>>;
+    fn choose_version(&self, package: &P, range: &VS) -> Result<Option<VS::V>, Self::Err>;
 
     /// Retrieves the package dependencies.
     /// Return [Dependencies::Unknown] if its dependencies are unknown.
     fn get_dependencies(
         &self,
         package: &P,
         version: &VS::V,
-    ) -> Result<Dependencies<P, VS>, Box<dyn Error + Send + Sync>>;
+    ) -> Result<Dependencies<P, VS>, Self::Err>;
 
     /// This is called fairly regularly during the resolution,
     /// if it returns an Err then resolution will be terminated.
     /// This is helpful if you want to add some form of early termination like a timeout,
     /// or you want to add some form of user feedback if things are taking a while.
     /// If not provided the resolver will run as long as needed.
-    fn should_cancel(&self) -> Result<(), Box<dyn Error + Send + Sync>> {
+    fn should_cancel(&self) -> Result<(), Self::Err> {
         Ok(())
     }
 }
@@ -340,11 +344,9 @@ impl<P: Package, VS: VersionSet> OfflineDependencyProvider<P, VS> {
 /// But, that may change in new versions if better heuristics are found.
 /// Versions are picked with the newest versions first.
 impl<P: Package, VS: VersionSet> DependencyProvider<P, VS> for OfflineDependencyProvider<P, VS> {
-    fn choose_version(
-        &self,
-        package: &P,
-        range: &VS,
-    ) -> Result<Option<VS::V>, Box<dyn Error + Send + Sync>> {
+    type Err = Infallible;
+
+    fn choose_version(&self, package: &P, range: &VS) -> Result<Option<VS::V>, Infallible> {
         Ok(self
             .dependencies
             .get(package)
@@ -365,7 +367,7 @@ impl<P: Package, VS: VersionSet> DependencyProvider<P, VS> for OfflineDependency
         &self,
         package: &P,
         version: &VS::V,
-    ) -> Result<Dependencies<P, VS>, Box<dyn Error + Send + Sync>> {
+    ) -> Result<Dependencies<P, VS>, Infallible> {
         Ok(match self.dependencies(package, version) {
             None => Dependencies::Unknown,
             Some(dependencies) => Dependencies::Known(dependencies),

tests/proptest.rs

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
-use std::{collections::BTreeSet as Set, error::Error};
+use std::collections::BTreeSet as Set;
+use std::convert::Infallible;
 
 use pubgrub::error::PubGrubError;
 use pubgrub::package::Package;
@@ -30,19 +31,11 @@ struct OldestVersionsDependencyProvider<P: Package, VS: VersionSet>(
 impl<P: Package, VS: VersionSet> DependencyProvider<P, VS>
     for OldestVersionsDependencyProvider<P, VS>
 {
-    fn get_dependencies(
-        &self,
-        p: &P,
-        v: &VS::V,
-    ) -> Result<Dependencies<P, VS>, Box<dyn Error + Send + Sync>> {
+    fn get_dependencies(&self, p: &P, v: &VS::V) -> Result<Dependencies<P, VS>, Infallible> {
         self.0.get_dependencies(p, v)
     }
 
-    fn choose_version(
-        &self,
-        package: &P,
-        range: &VS,
-    ) -> Result<Option<VS::V>, Box<dyn Error + Send + Sync>> {
+    fn choose_version(&self, package: &P, range: &VS) -> Result<Option<VS::V>, Infallible> {
         Ok(self
             .0
             .versions(package)
@@ -57,6 +50,8 @@ impl<P: Package, VS: VersionSet> DependencyProvider<P, VS>
     fn prioritize(&self, package: &P, range: &VS) -> Self::Priority {
         self.0.prioritize(package, range)
     }
+
+    type Err = Infallible;
 }
 
 /// The same as DP but it has a timeout.
@@ -82,27 +77,19 @@ impl<DP> TimeoutDependencyProvider<DP> {
 impl<P: Package, VS: VersionSet, DP: DependencyProvider<P, VS>> DependencyProvider<P, VS>
     for TimeoutDependencyProvider<DP>
 {
-    fn get_dependencies(
-        &self,
-        p: &P,
-        v: &VS::V,
-    ) -> Result<Dependencies<P, VS>, Box<dyn Error + Send + Sync>> {
+    fn get_dependencies(&self, p: &P, v: &VS::V) -> Result<Dependencies<P, VS>, DP::Err> {
         self.dp.get_dependencies(p, v)
     }
 
-    fn should_cancel(&self) -> Result<(), Box<dyn Error + Send + Sync>> {
+    fn should_cancel(&self) -> Result<(), DP::Err> {
         assert!(self.start_time.elapsed().as_secs() < 60);
         let calls = self.call_count.get();
         assert!(calls < self.max_calls);
         self.call_count.set(calls + 1);
         Ok(())
     }
 
-    fn choose_version(
-        &self,
-        package: &P,
-        range: &VS,
-    ) -> Result<Option<VS::V>, Box<dyn Error + Send + Sync>> {
+    fn choose_version(&self, package: &P, range: &VS) -> Result<Option<VS::V>, DP::Err> {
         self.dp.choose_version(package, range)
     }
 
@@ -111,13 +98,15 @@ impl<P: Package, VS: VersionSet, DP: DependencyProvider<P, VS>> DependencyProvid
     fn prioritize(&self, package: &P, range: &VS) -> Self::Priority {
         self.dp.prioritize(package, range)
     }
+
+    type Err = DP::Err;
 }
 
 fn timeout_resolve<P: Package, VS: VersionSet, DP: DependencyProvider<P, VS>>(
     dependency_provider: DP,
     name: P,
     version: impl Into<VS::V>,
-) -> Result<SelectedDependencies<P, VS::V>, PubGrubError<P, VS>> {
+) -> Result<SelectedDependencies<P, VS::V>, PubGrubError<P, VS, DP::Err>> {
     resolve(
         &TimeoutDependencyProvider::new(dependency_provider, 50_000),
         name,

tests/sat_dependency_provider.rs

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
+use std::convert::Infallible;
+
 use pubgrub::error::PubGrubError;
 use pubgrub::package::Package;
 use pubgrub::solver::{Dependencies, DependencyProvider, OfflineDependencyProvider};
@@ -135,7 +137,7 @@ impl<P: Package, VS: VersionSet> SatResolve<P, VS> {
 
     pub fn check_resolve(
         &mut self,
-        res: &Result<SelectedDependencies<P, VS::V>, PubGrubError<P, VS>>,
+        res: &Result<SelectedDependencies<P, VS::V>, PubGrubError<P, VS, Infallible>>,
         p: &P,
         v: &VS::V,
     ) {