Avoid early error for transistive constraints

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

@@ -1,9 +1,9 @@
 use itertools::Itertools;
-use pep440_rs::Version;
 use pubgrub::range::Range;
 use pubgrub::type_aliases::DependencyConstraints;
 use tracing::warn;
 
+use pep440_rs::Version;
 use pep508_rs::{MarkerEnvironment, Requirement, VersionOrUrl};
 use uv_normalize::{ExtraName, PackageName};
 
@@ -62,14 +62,24 @@ impl PubGrubDependencies {
 
                 if let Some(entry) = dependencies.get_key_value(&package) {
                     // Merge the versions.
-                    let version = merge_versions(&package, entry.1, &version)?;
+                    let intersection = entry.1.intersection(&version);
+                    if intersection.is_empty() {
+                        return Err(ResolveError::ConflictingVersions(
+                            package.to_string(),
+                            format!(
+                                "`{package}{left}` does not intersect with `{package}{right}`",
+                                left = entry.1,
+                                right = version
+                            ),
+                        ));
+                    }
 
                     // Merge the package.
                     if let Some(package) = merge_package(entry.0, &package)? {
                         dependencies.remove(&package);
-                        dependencies.insert(package, version);
+                        dependencies.insert(package, intersection);
                     } else {
-                        dependencies.insert(package, version);
+                        dependencies.insert(package, intersection);
                     }
                 } else {
                     dependencies.insert(package.clone(), version.clone());
@@ -117,14 +127,14 @@ impl PubGrubDependencies {
 
                 if let Some(entry) = dependencies.get_key_value(&package) {
                     // Merge the versions.
-                    let version = merge_versions(&package, entry.1, &version)?;
+                    let intersection = entry.1.intersection(&version);
 
                     // Merge the package.
                     if let Some(package) = merge_package(entry.0, &package)? {
                         dependencies.remove(&package);
-                        dependencies.insert(package, version);
+                        dependencies.insert(package, intersection);
                     } else {
-                        dependencies.insert(package, version);
+                        dependencies.insert(package, intersection);
                     }
                 }
             }
@@ -187,23 +197,6 @@ fn to_pubgrub(
     }
 }
 
-/// Merge two [`Version`] ranges.
-fn merge_versions(
-    package: &PubGrubPackage,
-    left: &Range<Version>,
-    right: &Range<Version>,
-) -> Result<Range<Version>, 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.
 fn merge_package(
     left: &PubGrubPackage,

crates/uv/tests/pip_compile.rs

@@ -3540,3 +3540,60 @@ fn compile_constraints_incompatible_url() -> Result<()> {
 
     Ok(())
 }
+
+/// Resolve a package from a `requirements.in` file, with a `constraints.txt` file pinning one of
+/// its transitive dependencies to a specific version.
+#[test]
+fn compile_constraints_compatible_version() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str("virtualenv")?;
+
+    let constraints_txt = context.temp_dir.child("constraints.txt");
+    constraints_txt.write_str("filelock==3.8.0")?;
+
+    uv_snapshot!(context.compile()
+            .arg("requirements.in")
+            .arg("--constraint")
+            .arg("constraints.txt"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × No solution found when resolving dependencies:
+      ╰─▶ Because only anyio>=4 is available and you require anyio<4, we can
+          conclude that the requirements are unsatisfiable.
+    "###
+    );
+
+    Ok(())
+}
+
+/// Resolve a package from a `requirements.in` file, with a `constraints.txt` file pinning one of
+/// its direct dependencies to an incompatible version.
+#[test]
+fn compile_constraints_incompatible_version() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str("filelock==1.0.0")?;
+
+    let constraints_txt = context.temp_dir.child("constraints.txt");
+    constraints_txt.write_str("filelock==3.8.0")?;
+
+    uv_snapshot!(context.compile()
+            .arg("requirements.in")
+            .arg("--constraint")
+            .arg("constraints.txt"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+
+    ----- stderr -----
+      × No solution found when resolving dependencies:
+      ╰─▶ you require ∅
+    "###
+    );
+
+    Ok(())
+}