Don't drop comments between items in TOML tables (#9784)

## Summary

If you look at Ed's reply
[here](toml-rs/toml#818 (comment)),
it sounds like we're being too heavy-handed in applying `.fmt()`. I
think I added this to handle an issue with inline tables whereby we were
inserting a space after a trailing comma? So now I'm just applying
`.fmt()` to inline tables, which don't allow comments between elements
anyway.

Closes #9758.

crates/uv-workspace/src/pyproject_mut.rs

@@ -413,7 +413,17 @@ impl PyProjectTomlMut {
         let name = req.name.clone();
         let added = add_dependency(req, group, source.is_some())?;
 
-        optional_dependencies.fmt();
+        // If `project.optional-dependencies` is an inline table, reformat it.
+        //
+        // Reformatting can drop comments between keys, but you can't put comments
+        // between items in an inline table anyway.
+        if let Some(optional_dependencies) = self
+            .project()?
+            .get_mut("optional-dependencies")
+            .and_then(Item::as_inline_table_mut)
+        {
+            optional_dependencies.fmt();
+        }
 
         if let Some(source) = source {
             self.add_source(&name, source)?;
@@ -448,7 +458,17 @@ impl PyProjectTomlMut {
         let name = req.name.clone();
         let added = add_dependency(req, group, source.is_some())?;
 
-        dependency_groups.fmt();
+        // If `dependency-groups` is an inline table, reformat it.
+        //
+        // Reformatting can drop comments between keys, but you can't put comments
+        // between items in an inline table anyway.
+        if let Some(dependency_groups) = self
+            .doc
+            .get_mut("dependency-groups")
+            .and_then(Item::as_inline_table_mut)
+        {
+            dependency_groups.fmt();
+        }
 
         if let Some(source) = source {
             self.add_source(&name, source)?;

crates/uv/tests/it/edit.rs

@@ -7089,6 +7089,147 @@ fn add_index_credentials() -> Result<()> {
     Ok(())
 }
 
+/// Add a PyPI requirement.
+#[test]
+fn add_group_comment() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [project]
+        name = "myproject"
+        version = "0.1.0"
+        description = "Add your description here"
+        requires-python = ">=3.11"
+        [dependency-groups]
+        # These are our dev dependencies
+        dev = [
+            "typing-extensions",
+        ]
+        # These are our test dependencies
+        test = [
+            "iniconfig"
+        ]
+    "#})?;
+
+    uv_snapshot!(context.filters(), context.add().arg("--group").arg("dev").arg("sniffio"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    Prepared 2 packages in [TIME]
+    Installed 2 packages in [TIME]
+     + sniffio==1.3.1
+     + typing-extensions==4.10.0
+    "###);
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r###"
+        [project]
+        name = "myproject"
+        version = "0.1.0"
+        description = "Add your description here"
+        requires-python = ">=3.11"
+        [dependency-groups]
+        # These are our dev dependencies
+        dev = [
+            "sniffio>=1.3.1",
+            "typing-extensions",
+        ]
+        # These are our test dependencies
+        test = [
+            "iniconfig"
+        ]
+        "###
+        );
+    });
+
+    let lock = context.read("uv.lock");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            lock, @r###"
+        version = 1
+        requires-python = ">=3.11"
+
+        [options]
+        exclude-newer = "2024-03-25T00:00:00Z"
+
+        [[package]]
+        name = "iniconfig"
+        version = "2.0.0"
+        source = { registry = "https://pypi.org/simple" }
+        sdist = { url = "https://files.pythonhosted.org/packages/d7/4b/cbd8e699e64a6f16ca3a8220661b5f83792b3017d0f79807cb8708d33913/iniconfig-2.0.0.tar.gz", hash = "sha256:2d91e135bf72d31a410b17c16da610a82cb55f6b0477d1a902134b24a455b8b3", size = 4646 }
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl", hash = "sha256:b6a85871a79d2e3b22d2d1b94ac2824226a63c6b741c88f7ae975f18b6778374", size = 5892 },
+        ]
+
+        [[package]]
+        name = "myproject"
+        version = "0.1.0"
+        source = { virtual = "." }
+
+        [package.dev-dependencies]
+        dev = [
+            { name = "sniffio" },
+            { name = "typing-extensions" },
+        ]
+        test = [
+            { name = "iniconfig" },
+        ]
+
+        [package.metadata]
+
+        [package.metadata.requires-dev]
+        dev = [
+            { name = "sniffio", specifier = ">=1.3.1" },
+            { name = "typing-extensions" },
+        ]
+        test = [{ name = "iniconfig" }]
+
+        [[package]]
+        name = "sniffio"
+        version = "1.3.1"
+        source = { registry = "https://pypi.org/simple" }
+        sdist = { url = "https://files.pythonhosted.org/packages/a2/87/a6771e1546d97e7e041b6ae58d80074f81b7d5121207425c964ddf5cfdbd/sniffio-1.3.1.tar.gz", hash = "sha256:f4324edc670a0f49750a81b895f35c3adb843cca46f0530f79fc1babb23789dc", size = 20372 }
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/e9/44/75a9c9421471a6c4805dbf2356f7c181a29c1879239abab1ea2cc8f38b40/sniffio-1.3.1-py3-none-any.whl", hash = "sha256:2f6da418d1f1e0fddd844478f41680e794e6051915791a034ff65e5f100525a2", size = 10235 },
+        ]
+
+        [[package]]
+        name = "typing-extensions"
+        version = "4.10.0"
+        source = { registry = "https://pypi.org/simple" }
+        sdist = { url = "https://files.pythonhosted.org/packages/16/3a/0d26ce356c7465a19c9ea8814b960f8a36c3b0d07c323176620b7b483e44/typing_extensions-4.10.0.tar.gz", hash = "sha256:b0abd7c89e8fb96f98db18d86106ff1d90ab692004eb746cf6eda2682f91b3cb", size = 77558 }
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/f9/de/dc04a3ea60b22624b51c703a84bbe0184abcd1d0b9bc8074b5d6b7ab90bb/typing_extensions-4.10.0-py3-none-any.whl", hash = "sha256:69b1a937c3a517342112fb4c6df7e72fc39a38e7891a5730ed4985b5214b5475", size = 33926 },
+        ]
+        "###
+        );
+    });
+
+    // Install from the lockfile.
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Audited 2 packages in [TIME]
+    "###);
+
+    Ok(())
+}
+
 #[test]
 fn add_index_comments() -> Result<()> {
     let context = TestContext::new("3.12");