Sort dependency group keys when adding new group

However, if earlier keys were not sorted, we just append to avoid churn.

crates/uv-workspace/src/pyproject_mut.rs

@@ -450,6 +450,13 @@ impl PyProjectTomlMut {
             .as_table_like_mut()
             .ok_or(Error::MalformedDependencies)?;
 
+        let was_sorted = dependency_groups
+            .get_values()
+            .iter()
+            .filter_map(|(dotted_ks, _)| dotted_ks.first())
+            .map(|k| k.get())
+            .is_sorted();
+
         let group = dependency_groups
             .entry(group.as_ref())
             .or_insert(Item::Value(Value::Array(Array::new())))
@@ -459,6 +466,12 @@ impl PyProjectTomlMut {
         let name = req.name.clone();
         let added = add_dependency(req, group, source.is_some())?;
 
+        // To avoid churn in pyproject.toml, we only sort new group keys if the
+        // existing keys were sorted.
+        if was_sorted {
+            dependency_groups.sort_values();
+        }
+
         // If `dependency-groups` is an inline table, reformat it.
         //
         // Reformatting can drop comments between keys, but you can't put comments

crates/uv/tests/it/edit.rs

@@ -4826,6 +4826,112 @@ fn add_group() -> Result<()> {
 
     let pyproject_toml = context.read("pyproject.toml");
 
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = []
+
+        [dependency-groups]
+        second = [
+            "anyio==3.7.0",
+        ]
+        test = [
+            "anyio==3.7.0",
+            "requests>=2.31.0",
+        ]
+        "#
+        );
+    });
+
+    uv_snapshot!(context.filters(), context.add().arg("anyio==3.7.0").arg("--group").arg("alpha"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 8 packages in [TIME]
+    Audited 3 packages in [TIME]
+    "###);
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = []
+
+        [dependency-groups]
+        alpha = [
+            "anyio==3.7.0",
+        ]
+        second = [
+            "anyio==3.7.0",
+        ]
+        test = [
+            "anyio==3.7.0",
+            "requests>=2.31.0",
+        ]
+        "#
+        );
+    });
+
+    assert!(context.temp_dir.join("uv.lock").exists());
+
+    Ok(())
+}
+
+/// Add a requirement to a dependency group when existing dependency group
+/// keys are not sorted.
+#[test]
+fn add_group_to_unsorted() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = []
+
+        [dependency-groups]
+        test = [
+            "anyio==3.7.0",
+            "requests>=2.31.0",
+        ]
+        second = [
+            "anyio==3.7.0",
+        ]
+    "#})?;
+
+    uv_snapshot!(context.filters(), context.add().arg("anyio==3.7.0").arg("--group").arg("alpha"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 8 packages in [TIME]
+    Prepared 3 packages in [TIME]
+    Installed 3 packages in [TIME]
+     + anyio==3.7.0
+     + idna==3.6
+     + sniffio==1.3.1
+    "###);
+
+    let pyproject_toml = context.read("pyproject.toml");
+
     insta::with_settings!({
         filters => context.filters(),
     }, {
@@ -4845,6 +4951,9 @@ fn add_group() -> Result<()> {
         second = [
             "anyio==3.7.0",
         ]
+        alpha = [
+            "anyio==3.7.0",
+        ]
         "###
         );
     });