Unify dependency iteration in ResolverState::get_dependencies (#4515)

Upstack PR: #4430

Split out from #4430 according to
https://github.com/astral-sh/uv/pull/4430#discussion_r1650192338.

crates/uv-resolver/src/resolver/availability.rs

@@ -40,8 +40,6 @@ pub(crate) enum UnavailableVersion {
     InvalidStructure,
     /// The wheel metadata was not found in the cache and the network is not available.
     Offline,
-    /// Forward any kind of resolver error.
-    ResolverError(String),
 }
 
 impl Display for UnavailableVersion {
@@ -57,7 +55,6 @@ impl Display for UnavailableVersion {
             UnavailableVersion::Offline => f.write_str(
                 "network connectivity is disabled, but the metadata wasn't found in the cache",
             ),
-            UnavailableVersion::ResolverError(err) => f.write_str(err),
         }
     }
 }

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

@@ -936,7 +936,7 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
         priorities: &mut PubGrubPriorities,
         request_sink: &Sender<Request>,
     ) -> Result<Dependencies, ResolveError> {
-        match &**package {
+        let (dependencies, name) = match &**package {
             PubGrubPackageInner::Root(_) => {
                 // Add the root requirements.
                 let dependencies = PubGrubDependencies::from_requirements(
@@ -953,31 +953,11 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                     self.markers.as_ref(),
                     self.requires_python.as_ref(),
                     markers,
-                );
+                )?;
-
+                (dependencies, None)
-                let dependencies = match dependencies {
-                    Ok(dependencies) => dependencies,
-                    Err(err) => {
-                        return Ok(Dependencies::Unavailable(
-                            UnavailableVersion::ResolverError(uncapitalize(err.to_string())),
-                        ));
-                    }
-                };
-
-                for (package, version) in dependencies.iter() {
-                    debug!("Adding direct dependency: {package}{version}");
-
-                    // Update the package priorities.
-                    priorities.insert(package, version);
-
-                    // Emit a request to fetch the metadata for this package.
-                    self.visit_package(package, request_sink)?;
             }
 
-                Ok(Dependencies::Available(dependencies.into()))
+            PubGrubPackageInner::Python(_) => return Ok(Dependencies::Available(Vec::default())),
-            }
-
-            PubGrubPackageInner::Python(_) => Ok(Dependencies::Available(Vec::default())),
 
             PubGrubPackageInner::Package {
                 name,
@@ -1108,16 +1088,6 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                     markers,
                 )?;
 
-                for (dep_package, dep_version) in dependencies.iter() {
-                    debug!("Adding transitive dependency for {package}=={version}: {dep_package}{dep_version}");
-
-                    // Update the package priorities.
-                    priorities.insert(dep_package, dep_version);
-
-                    // Emit a request to fetch the metadata for this package.
-                    self.visit_package(dep_package, request_sink)?;
-                }
-
                 // If a package has metadata for an enabled dependency group,
                 // add a dependency from it to the same package with the group
                 // enabled.
@@ -1137,11 +1107,12 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                     }
                 }
 
-                Ok(Dependencies::Available(dependencies.into()))
+                (dependencies, Some(name))
             }
 
             // Add a dependency on both the marker and base package.
-            PubGrubPackageInner::Marker { name, marker, url } => Ok(Dependencies::Available(
+            PubGrubPackageInner::Marker { name, marker, url } => {
+                return Ok(Dependencies::Available(
                     [None, Some(marker)]
                         .into_iter()
                         .map(move |marker| {
@@ -1157,7 +1128,8 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                             )
                         })
                         .collect(),
-            )),
+                ))
+            }
 
             // Add a dependency on both the extra and base package, with and without the marker.
             PubGrubPackageInner::Extra {
@@ -1165,7 +1137,8 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                 extra,
                 marker,
                 url,
-            } => Ok(Dependencies::Available(
+            } => {
+                return Ok(Dependencies::Available(
                     [None, marker.as_ref()]
                         .into_iter()
                         .dedup()
@@ -1184,7 +1157,8 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                             })
                         })
                         .collect(),
-            )),
+                ))
+            }
 
             // Add a dependency on both the development dependency group and base package, with and
             // without the marker.
@@ -1193,7 +1167,8 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                 dev,
                 marker,
                 url,
-            } => Ok(Dependencies::Available(
+            } => {
+                return Ok(Dependencies::Available(
                     [None, marker.as_ref()]
                         .into_iter()
                         .dedup()
@@ -1212,8 +1187,25 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                             })
                         })
                         .collect(),
-            )),
+                ))
             }
+        };
+
+        for (dep_package, dep_version) in dependencies.iter() {
+            if let Some(name) = name {
+                debug!("Adding transitive dependency for {name}=={version}: {dep_package}{dep_version}");
+            } else {
+                debug!("Adding direct dependency: {dep_package}{dep_version}");
+            }
+
+            // Update the package priorities.
+            priorities.insert(dep_package, dep_version);
+
+            // Emit a request to fetch the metadata for this package.
+            self.visit_package(dep_package, request_sink)?;
+        }
+
+        Ok(Dependencies::Available(dependencies.into()))
     }
 
     /// Fetch the metadata for a stream of packages and versions.
@@ -2298,11 +2290,3 @@ impl<'a> PossibleFork<'a> {
         false
     }
 }
-
-fn uncapitalize<T: AsRef<str>>(string: T) -> String {
-    let mut chars = string.as_ref().chars();
-    match chars.next() {
-        None => String::new(),
-        Some(first) => first.to_lowercase().chain(chars).collect(),
-    }
-}