Add an UnusableDependencies incompatibility kind and use for conflicting versions

Cargo.toml

@@ -48,7 +48,7 @@ once_cell = { version = "1.18.0" }
 petgraph = { version = "0.6.4" }
 platform-info = { version = "2.0.2" }
 plist = { version = "1.6.0" }
-pubgrub = { git = "https://github.com/zanieb/pubgrub", rev = "46f1214fe6b7886709a35d8d2f2c0e1b56433b26" }
+pubgrub = { git = "https://github.com/zanieb/pubgrub", rev = "efe34571a876831dacac1cbba3ce5bc358f2a6e7" }
 pyproject-toml = { version = "0.8.0" }
 rand = { version = "0.8.5" }
 rayon = { version = "1.8.0" }

crates/puffin-cli/tests/snapshots/pip_compile__compile_unsolvable_requirements.snap

@@ -6,15 +6,16 @@ info:
     - pip-compile
     - pyproject.toml
     - "--cache-dir"
-    - /var/folders/bc/qlsk3t6x7c9fhhbvvcg68k9c0000gp/T/.tmpN531dN
+    - /var/folders/bc/qlsk3t6x7c9fhhbvvcg68k9c0000gp/T/.tmpJ9Dkj3
   env:
-    VIRTUAL_ENV: /var/folders/bc/qlsk3t6x7c9fhhbvvcg68k9c0000gp/T/.tmp99w9dK/.venv
+    VIRTUAL_ENV: /var/folders/bc/qlsk3t6x7c9fhhbvvcg68k9c0000gp/T/.tmpBOyFGn/.venv
 ---
 success: false
 exit_code: 1
 ----- stdout -----
 
 ----- stderr -----
   × No solution found when resolving dependencies:
-  ╰─▶ my-project depends on django∅
+  ╰─▶ my-project dependencies are unusable: Conflicting versions for `django`:
+      `django==5.0b1` does not intersect with `django==5.0a1`
 

crates/puffin-resolver/src/error.rs

@@ -44,6 +44,9 @@ pub enum ResolveError {
     #[error("Conflicting URLs for package `{0}`: {1} and {2}")]
     ConflictingUrls(PackageName, String, String),
 
+    #[error("Conflicting versions for `{0}`: {1}")]
+    ConflictingVersions(String, String),
+
     #[error("Package `{0}` attempted to resolve via URL: {1}. URL dependencies must be expressed as direct requirements or constraints. Consider adding `{0} @ {1}` to your dependencies or constraints file.")]
     DisallowedUrl(PackageName, Url),
 

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

@@ -59,7 +59,7 @@ impl PubGrubDependencies {
 
                 if let Some(entry) = dependencies.get_key_value(&package) {
                     // Merge the versions.
-                    let version = merge_versions(entry.1, &version);
+                    let version = merge_versions(&package, entry.1, &version)?;
 
                     // Merge the package.
                     if let Some(package) = merge_package(entry.0, &package)? {
@@ -107,7 +107,7 @@ impl PubGrubDependencies {
 
                 if let Some(entry) = dependencies.get_key_value(&package) {
                     // Merge the versions.
-                    let version = merge_versions(entry.1, &version);
+                    let version = merge_versions(&package, entry.1, &version)?;
 
                     // Merge the package.
                     if let Some(package) = merge_package(entry.0, &package)? {
@@ -178,10 +178,19 @@ fn to_pubgrub(
 
 /// Merge two [`PubGrubVersion`] ranges.
 fn merge_versions(
+    package: &PubGrubPackage,
     left: &Range<PubGrubVersion>,
     right: &Range<PubGrubVersion>,
-) -> Range<PubGrubVersion> {
-    left.intersection(right)
+) -> Result<Range<PubGrubVersion>, ResolveError> {
+    let result = left.intersection(right);
+    if result.is_empty() {
+        Err(ResolveError::ConflictingVersions(
+            package.to_string(),
+            format!("`{package}{left}` does not intersect with `{package}{right}`"),
+        ))
+    } else {
+        Ok(result)
+    }
 }
 
 /// Merge two [`PubGrubPackage`] instances.

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

@@ -345,6 +345,8 @@ enum PuffinExternal {
     NoVersions(PubGrubPackage, Range<PubGrubVersion>),
     /// Dependencies of the package are unavailable for versions in that set.
     UnavailableDependencies(PubGrubPackage, Range<PubGrubVersion>),
+    /// Dependencies of the package are unusable for versions in that set.
+    UnusableDependencies(PubGrubPackage, Range<PubGrubVersion>, Option<String>),
     /// Incompatibility coming from the dependencies of a given package.
     FromDependencyOf(
         PubGrubPackage,
@@ -362,6 +364,9 @@ impl PuffinExternal {
             External::UnavailableDependencies(p, vs) => {
                 PuffinExternal::UnavailableDependencies(p, vs)
             }
+            External::UnusableDependencies(p, vs, reason) => {
+                PuffinExternal::UnusableDependencies(p, vs, reason)
+            }
             External::FromDependencyOf(p, vs, p_dep, vs_dep) => {
                 PuffinExternal::FromDependencyOf(p, vs, p_dep, vs_dep)
             }
@@ -395,6 +400,25 @@ impl fmt::Display for PuffinExternal {
                     )
                 }
             }
+            Self::UnusableDependencies(package, set, reason) => {
+                if let Some(reason) = reason {
+                    if matches!(package, PubGrubPackage::Root(_)) {
+                        write!(f, "{package} dependencies are unusable: {reason}")
+                    } else {
+                        if set == &Range::full() {
+                            write!(f, "dependencies of {package} are unusable: {reason}")
+                        } else {
+                            write!(f, "dependencies of {package}{set} are unusable: {reason}",)
+                        }
+                    }
+                } else {
+                    if set == &Range::full() {
+                        write!(f, "dependencies of {package} are unusable")
+                    } else {
+                        write!(f, "dependencies of {package}{set} are unusable")
+                    }
+                }
+            }
             Self::FromDependencyOf(package, package_set, dependency, dependency_set) => {
                 if package_set == &Range::full() && dependency_set == &Range::full() {
                     write!(f, "{package} depends on {dependency}")

crates/puffin-resolver/src/resolver.rs

@@ -241,6 +241,14 @@ impl<'a, Context: BuildContext + Sync> Resolver<'a, Context> {
                         ));
                         continue;
                     }
+                    Dependencies::Unusable(reason) => {
+                        state.add_incompatibility(Incompatibility::unusable_dependencies(
+                            package.clone(),
+                            version.clone(),
+                            reason.clone(),
+                        ));
+                        continue;
+                    }
                     Dependencies::Known(constraints) if constraints.contains_key(package) => {
                         return Err(PubGrubError::SelfDependency {
                             package: package.clone(),
@@ -457,7 +465,11 @@ impl<'a, Context: BuildContext + Sync> Resolver<'a, Context> {
                     None,
                     None,
                     self.markers,
-                )?;
+                );
+                if let Err(err @ ResolveError::ConflictingVersions(..)) = constraints {
+                    return Ok(Dependencies::Unusable(Some(err.to_string())));
+                }
+                let constraints = constraints?;
 
                 for (package, version) in constraints.iter() {
                     debug!("Adding direct dependency: {package}{version}");
@@ -862,6 +874,8 @@ impl<'a> FromIterator<&'a Url> for AllowedUrls {
 enum Dependencies {
     /// Package dependencies are unavailable.
     Unknown,
+    /// Package dependencies are not usable
+    Unusable(Option<String>),
     /// Container for all available package versions.
     Known(DependencyConstraints<PubGrubPackage, Range<PubGrubVersion>>),
 }