Use current and requested Python versions in requires-python incompatibility errors (#986)

Closes https://github.com/astral-sh/puffin/issues/806

crates/puffin-resolver/src/error.rs

@@ -108,8 +108,10 @@ impl From<pubgrub::error::PubGrubError<PubGrubPackage, Range<Version>, Infallibl
             pubgrub::error::PubGrubError::NoSolution(derivation_tree) => {
                 ResolveError::NoSolution(NoSolutionError {
                     derivation_tree,
+                    // The following should be populated before display for the best error messages
                     available_versions: FxHashMap::default(),
                     selector: None,
+                    python_requirement: None,
                 })
             }
             pubgrub::error::PubGrubError::SelfDependency { package, version } => {
@@ -128,6 +130,7 @@ pub struct NoSolutionError {
     derivation_tree: DerivationTree<PubGrubPackage, Range<Version>>,
     available_versions: FxHashMap<PubGrubPackage, Vec<Version>>,
     selector: Option<CandidateSelector>,
+    python_requirement: Option<PythonRequirement>,
 }
 
 impl std::error::Error for NoSolutionError {}
@@ -137,6 +140,7 @@ impl std::fmt::Display for NoSolutionError {
         // Write the derivation report.
         let formatter = PubGrubReportFormatter {
             available_versions: &self.available_versions,
+            python_requirement: self.python_requirement.as_ref(),
         };
         let report =
             DefaultStringReporter::report_with_formatter(&self.derivation_tree, &formatter);
@@ -201,4 +205,14 @@ impl NoSolutionError {
         self.selector = Some(selector);
         self
     }
+
+    /// Update the Python requirements attached to the error.
+    #[must_use]
+    pub(crate) fn with_python_requirement(
+        mut self,
+        python_requirement: &PythonRequirement,
+    ) -> Self {
+        self.python_requirement = Some(python_requirement.clone());
+        self
+    }
 }

crates/puffin-resolver/src/pubgrub/report.rs

@@ -13,6 +13,7 @@ use rustc_hash::{FxHashMap, FxHashSet};
 
 use crate::candidate_selector::CandidateSelector;
 use crate::prerelease_mode::PreReleaseStrategy;
+use crate::python_requirement::PythonRequirement;
 
 use super::PubGrubPackage;
 
@@ -20,6 +21,9 @@ use super::PubGrubPackage;
 pub(crate) struct PubGrubReportFormatter<'a> {
     /// The versions that were available for each package
     pub(crate) available_versions: &'a FxHashMap<PubGrubPackage, Vec<Version>>,
+
+    /// The versions that were available for each package
+    pub(crate) python_requirement: Option<&'a PythonRequirement>,
 }
 
 impl ReportFormatter<PubGrubPackage, Range<Version>> for PubGrubReportFormatter<'_> {
@@ -31,6 +35,53 @@ impl ReportFormatter<PubGrubPackage, Range<Version>> for PubGrubReportFormatter<
                 format!("we are solving dependencies of {package} {version}")
             }
             External::NoVersions(package, set) => {
+                if matches!(package, PubGrubPackage::Python(_)) {
+                    if let Some(python) = self.python_requirement {
+                        if python.target().release().iter().eq(python
+                            .installed()
+                            .release()
+                            .iter()
+                            .take(2))
+                        {
+                            // Simple case, the installed version is the same as the target version
+                            // N.B. Usually the target version does not include anything past the
+                            //      minor version mumber so we only compare to part of the installed
+                            //      version. If the target version is longer, we'll do the complex
+                            //      display instead.
+                            return format!(
+                                "the current {package} version ({}) does not satisfy {}",
+                                python.target(),
+                                PackageRange::compatibility(package, set)
+                            );
+                        }
+                        // Complex case, the target was provided and differs from the installed one
+                        // Determine which Python version requirement was not met
+                        if !set.contains(python.target()) {
+                            return format!(
+                                "the requested {package} version ({}) does not satisfy {}",
+                                python.target(),
+                                PackageRange::compatibility(package, set)
+                            );
+                        }
+                        // TODO(zanieb): Explain to the user why the installed version is relevant
+                        //               when they provided a target version; probably via a "hint"
+                        debug_assert!(
+                            !set.contains(python.installed()),
+                            "There should not be an incompatibility where the range is satisfied by both Python requirements"
+                        );
+                        return format!(
+                            "the current {package} version ({}) does not satisfy {}",
+                            python.installed(),
+                            PackageRange::compatibility(package, set)
+                        );
+                    }
+                    // We should always have the required Python versions, if we don't we'll fall back
+                    // to a less helpful message in production
+                    debug_assert!(
+                        false,
+                        "Error reporting should always be provided with Python versions"
+                    );
+                }
                 let set = self.simplify_set(set, package);
                 if set.as_ref() == &Range::full() {
                     format!("there are no versions of {package}")

crates/puffin-resolver/src/python_requirement.rs

@@ -3,30 +3,30 @@ use pep508_rs::MarkerEnvironment;
 use puffin_interpreter::Interpreter;
 
 #[derive(Debug, Clone)]
-pub struct PythonRequirement<'a> {
+pub struct PythonRequirement {
     /// The installed version of Python.
-    installed: &'a Version,
+    installed: Version,
     /// The target version of Python; that is, the version of Python for which we are resolving
     /// dependencies. This is typically the same as the installed version, but may be different
     /// when specifying an alternate Python version for the resolution.
-    target: &'a Version,
+    target: Version,
 }
 
-impl<'a> PythonRequirement<'a> {
-    pub fn new(interpreter: &'a Interpreter, markers: &'a MarkerEnvironment) -> Self {
+impl PythonRequirement {
+    pub fn new(interpreter: &Interpreter, markers: &MarkerEnvironment) -> Self {
         Self {
-            installed: interpreter.version(),
-            target: &markers.python_version.version,
+            installed: interpreter.version().clone(),
+            target: markers.python_version.version.clone(),
         }
     }
 
     /// Return the installed version of Python.
-    pub(crate) fn installed(&self) -> &'a Version {
-        self.installed
+    pub(crate) fn installed(&self) -> &Version {
+        &self.installed
     }
 
     /// Return the target version of Python.
-    pub(crate) fn target(&self) -> &'a Version {
-        self.target
+    pub(crate) fn target(&self) -> &Version {
+        &self.target
     }
 }

crates/puffin-resolver/src/resolver/mod.rs

@@ -63,7 +63,7 @@ pub struct Resolver<'a, Provider: ResolverProvider> {
     overrides: Overrides,
     allowed_urls: AllowedUrls,
     markers: &'a MarkerEnvironment,
-    python_requirement: PythonRequirement<'a>,
+    python_requirement: PythonRequirement,
     selector: CandidateSelector,
     index: &'a InMemoryIndex,
     /// A map from [`PackageId`] to the `Requires-Python` version specifiers for that package.
@@ -120,7 +120,7 @@ impl<'a, Provider: ResolverProvider> Resolver<'a, Provider> {
         manifest: Manifest,
         options: ResolutionOptions,
         markers: &'a MarkerEnvironment,
-        python_requirement: PythonRequirement<'a>,
+        python_requirement: PythonRequirement,
         index: &'a InMemoryIndex,
         provider: Provider,
     ) -> Self {
@@ -221,7 +221,12 @@ impl<'a, Provider: ResolverProvider> Resolver<'a, Provider> {
 
                     // Add version information to improve unsat error messages.
                     if let ResolveError::NoSolution(err) = err {
-                        ResolveError::NoSolution(err.with_available_versions(&self.python_requirement, &self.index.packages).with_selector(self.selector.clone()))
+                        ResolveError::NoSolution(
+                            err
+                            .with_available_versions(&self.python_requirement, &self.index.packages)
+                            .with_selector(self.selector.clone())
+                            .with_python_requirement(&self.python_requirement)
+                        )
                     } else {
                         err
                     }

crates/puffin-resolver/src/resolver/provider.rs

@@ -52,7 +52,7 @@ pub struct DefaultResolverProvider<'a, Context: BuildContext + Send + Sync> {
     /// These are the entries from `--find-links` that act as overrides for index responses.
     flat_index: &'a FlatIndex,
     tags: &'a Tags,
-    python_requirement: PythonRequirement<'a>,
+    python_requirement: PythonRequirement,
     exclude_newer: Option<DateTime<Utc>>,
     allowed_yanks: AllowedYanks,
     no_binary: &'a NoBinary,
@@ -66,7 +66,7 @@ impl<'a, Context: BuildContext + Send + Sync> DefaultResolverProvider<'a, Contex
         fetcher: DistributionDatabase<'a, Context>,
         flat_index: &'a FlatIndex,
         tags: &'a Tags,
-        python_requirement: PythonRequirement<'a>,
+        python_requirement: PythonRequirement,
         exclude_newer: Option<DateTime<Utc>>,
         allowed_yanks: AllowedYanks,
         no_binary: &'a NoBinary,

crates/puffin/tests/pip_compile.rs

@@ -687,8 +687,9 @@ fn compile_python_37() -> Result<()> {
 
         ----- stderr -----
           × No solution found when resolving dependencies:
-          ╰─▶ Because only Python<3.8 is available and black==23.10.1 depends on
-              Python>=3.8, we can conclude that black==23.10.1 cannot be used.
+          ╰─▶ Because the requested Python version (3.7.17) does not satisfy
+              Python>=3.8 and black==23.10.1 depends on Python>=3.8, we can conclude
+              that black==23.10.1 cannot be used.
               And because you require black==23.10.1 we can conclude that the
               requirements are unsatisfiable.
         "###);

crates/puffin/tests/pip_install_scenarios.rs

@@ -2554,7 +2554,7 @@ fn requires_python_version_does_not_exist() -> Result<()> {
 
         ----- stderr -----
           × No solution found when resolving dependencies:
-          ╰─▶ Because only Python<4.0 is available and albatross==1.0.0 depends on Python>=4.0, we can conclude that albatross==1.0.0 cannot be used.
+          ╰─▶ Because the current Python version (3.7) does not satisfy Python>=4.0 and albatross==1.0.0 depends on Python>=4.0, we can conclude that albatross==1.0.0 cannot be used.
               And because you require albatross==1.0.0 we can conclude that the requirements are unsatisfiable.
         "###);
     });
@@ -2611,7 +2611,7 @@ fn requires_python_version_less_than_current() -> Result<()> {
 
         ----- stderr -----
           × No solution found when resolving dependencies:
-          ╰─▶ Because only Python>3.8 is available and albatross==1.0.0 depends on Python<=3.8, we can conclude that albatross==1.0.0 cannot be used.
+          ╰─▶ Because the current Python version (3.9) does not satisfy Python<=3.8 and albatross==1.0.0 depends on Python<=3.8, we can conclude that albatross==1.0.0 cannot be used.
               And because you require albatross==1.0.0 we can conclude that the requirements are unsatisfiable.
         "###);
     });
@@ -2668,7 +2668,7 @@ fn requires_python_version_greater_than_current() -> Result<()> {
 
         ----- stderr -----
           × No solution found when resolving dependencies:
-          ╰─▶ Because only Python<3.10 is available and albatross==1.0.0 depends on Python>=3.10, we can conclude that albatross==1.0.0 cannot be used.
+          ╰─▶ Because the current Python version (3.9) does not satisfy Python>=3.10 and albatross==1.0.0 depends on Python>=3.10, we can conclude that albatross==1.0.0 cannot be used.
               And because you require albatross==1.0.0 we can conclude that the requirements are unsatisfiable.
         "###);
     });
@@ -2876,22 +2876,22 @@ fn requires_python_version_greater_than_current_excluded() -> Result<()> {
 
         ----- stderr -----
           × No solution found when resolving dependencies:
-          ╰─▶ Because there are no versions of Python that satisfy Python>=3.10,<3.11 and only Python<3.12 is available, we can conclude that any of:
+          ╰─▶ Because the current Python version (3.9) does not satisfy Python>=3.10,<3.11 and the current Python version (3.9) does not satisfy Python>=3.12, we can conclude that any of:
                   Python>=3.10,<3.11
                   Python>=3.12
                are incompatible.
-              And because there are no versions of Python that satisfy Python>=3.11,<3.12 we can conclude that Python>=3.10 are incompatible.
+              And because the current Python version (3.9) does not satisfy Python>=3.11,<3.12 we can conclude that Python>=3.10 are incompatible.
               And because albatross==2.0.0 depends on Python>=3.10 and there are no versions of albatross that satisfy any of:
                   albatross>2.0.0,<3.0.0
                   albatross>3.0.0,<4.0.0
                   albatross>4.0.0
               we can conclude that albatross>=2.0.0,<3.0.0 cannot be used. (1)
 
-              Because there are no versions of Python that satisfy Python>=3.11,<3.12 and only Python<3.12 is available, we can conclude that Python>=3.11 are incompatible.
+              Because the current Python version (3.9) does not satisfy Python>=3.11,<3.12 and the current Python version (3.9) does not satisfy Python>=3.12, we can conclude that Python>=3.11 are incompatible.
               And because albatross==3.0.0 depends on Python>=3.11 we can conclude that albatross==3.0.0 cannot be used.
               And because we know from (1) that albatross>=2.0.0,<3.0.0 cannot be used, we can conclude that albatross>=2.0.0,<4.0.0 cannot be used. (2)
 
-              Because only Python<3.12 is available and albatross==4.0.0 depends on Python>=3.12, we can conclude that albatross==4.0.0 cannot be used.
+              Because the current Python version (3.9) does not satisfy Python>=3.12 and albatross==4.0.0 depends on Python>=3.12, we can conclude that albatross==4.0.0 cannot be used.
               And because we know from (2) that albatross>=2.0.0,<4.0.0 cannot be used, we can conclude that albatross>=2.0.0 cannot be used.
               And because you require albatross>=2.0.0 we can conclude that the requirements are unsatisfiable.
         "###);