Avoid enforcing non-conflicts in `uv export` (#9751)

## Summary

These are already enforced a level above.

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

@@ -4143,11 +4143,6 @@ enum LockErrorKind {
         #[source]
         err: DependencyGroupError,
     },
-    /// An error that occurs when trying to export a `uv.lock` with
-    /// conflicting extras/groups specified to `requirements.txt`.
-    /// (Because `requirements.txt` cannot encode them.)
-    #[error("Cannot represent `uv.lock` with conflicting extras or groups as `requirements.txt`")]
-    ConflictsNotAllowedInRequirementsTxt,
 }
 
 /// An error that occurs when a source string could not be parsed.

crates/uv-resolver/src/lock/requirements_txt.rs

@@ -19,7 +19,7 @@ use uv_pep508::MarkerTree;
 use uv_pypi_types::{ParsedArchiveUrl, ParsedGitUrl};
 
 use crate::graph_ops::marker_reachability;
-use crate::lock::{LockErrorKind, Package, PackageId, Source};
+use crate::lock::{Package, PackageId, Source};
 use crate::universal_marker::UniversalMarker;
 use crate::{InstallTarget, LockError};
 
@@ -41,9 +41,6 @@ impl<'lock> RequirementsTxtExport<'lock> {
         hashes: bool,
         install_options: &'lock InstallOptions,
     ) -> Result<Self, LockError> {
-        if !target.lock().conflicts().is_empty() {
-            return Err(LockErrorKind::ConflictsNotAllowedInRequirementsTxt.into());
-        }
         let size_guess = target.lock().packages.len();
         let mut petgraph = Graph::with_capacity(size_guess, size_guess);
         let mut inverse = FxHashMap::with_capacity_and_hasher(size_guess, FxBuildHasher);

crates/uv/tests/it/export.rs

@@ -1687,3 +1687,100 @@ fn export_group() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn conflicts() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig==1.1.1"]
+
+        [tool.uv]
+        conflicts = [
+            [
+              { extra = "extra1" },
+              { extra = "extra2" },
+            ],
+        ]
+
+        [project.optional-dependencies]
+        extra1 = ["sortedcontainers==2.3.0"]
+        extra2 = ["sortedcontainers==2.4.0"]
+
+        [build-system]
+        requires = ["setuptools>=42"]
+        build-backend = "setuptools.build_meta"
+        "#,
+    )?;
+
+    context.lock().assert().success();
+
+    uv_snapshot!(context.filters(), context.export(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv export --cache-dir [CACHE_DIR]
+    -e .
+    iniconfig==1.1.1 \
+        --hash=sha256:011e24c64b7f47f6ebd835bb12a743f2fbe9a26d4cecaa7f53bc4f35ee9da8b3 \
+        --hash=sha256:bc3af051d7d14b2ee5ef9969666def0cd1a000e121eaea580d4a313df4b37f32
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    "###);
+
+    uv_snapshot!(context.filters(), context.export().arg("--extra").arg("extra1"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv export --cache-dir [CACHE_DIR] --extra extra1
+    -e .
+    iniconfig==1.1.1 \
+        --hash=sha256:011e24c64b7f47f6ebd835bb12a743f2fbe9a26d4cecaa7f53bc4f35ee9da8b3 \
+        --hash=sha256:bc3af051d7d14b2ee5ef9969666def0cd1a000e121eaea580d4a313df4b37f32
+    sortedcontainers==2.3.0 \
+        --hash=sha256:37257a32add0a3ee490bb170b599e93095eed89a55da91fa9f48753ea12fd73f \
+        --hash=sha256:59cc937650cf60d677c16775597c89a960658a09cf7c1a668f86e1e4464b10a1
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    "###);
+
+    uv_snapshot!(context.filters(), context.export().arg("--extra").arg("extra2"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv export --cache-dir [CACHE_DIR] --extra extra2
+    -e .
+    iniconfig==1.1.1 \
+        --hash=sha256:011e24c64b7f47f6ebd835bb12a743f2fbe9a26d4cecaa7f53bc4f35ee9da8b3 \
+        --hash=sha256:bc3af051d7d14b2ee5ef9969666def0cd1a000e121eaea580d4a313df4b37f32
+    sortedcontainers==2.4.0 \
+        --hash=sha256:25caa5a06cc30b6b83d11423433f65d1f9d76c4c6a0c90e3379eaa43b9bfdb88 \
+        --hash=sha256:a163dcaede0f1c021485e957a39245190e74249897e2ae4b2aa38595db237ee0
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    "###);
+
+    uv_snapshot!(context.filters(), context.export().arg("--extra").arg("extra1").arg("--extra").arg("extra2"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    error: Extras `extra1` and `extra2` are incompatible with the declared conflicts: {`project[extra1]`, `project[extra2]`}
+    "###);
+
+    Ok(())
+}