Avoid dropping pip-sync requirements with markers

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

@@ -968,7 +968,21 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                         .wait_blocking(&version_id)
                         .ok_or(ResolveError::Unregistered)?;
 
-                    return Ok(Dependencies::Available(Vec::default()));
+                    // If a package has a marker, add a dependency from it to the
+                    // same package without markers.
+                    return Ok(Dependencies::Available(if marker.is_some() {
+                        vec![(
+                            PubGrubPackage::from(PubGrubPackageInner::Package {
+                                name: name.clone(),
+                                extra: extra.clone(),
+                                marker: None,
+                                url: url.clone(),
+                            }),
+                            Range::singleton(version.clone()),
+                        )]
+                    } else {
+                        vec![]
+                    }));
                 }
 
                 // Determine the distribution to lookup.

crates/uv/tests/pip_sync.rs

@@ -5164,3 +5164,28 @@ fn target_no_build_isolation() -> Result<()> {
 
     Ok(())
 }
+
+/// Ensure that we install packages with markers on them.
+#[test]
+fn preserve_markers() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let requirements_txt = context.temp_dir.child("requirements.txt");
+    requirements_txt.write_str("anyio ; python_version > '3.7'")?;
+
+    uv_snapshot!(sync_without_exclude_newer(&context)
+        .arg("requirements.txt"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    Downloaded 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + anyio==4.4.0
+    "###
+    );
+
+    Ok(())
+}