uv init: Implies --package when using --build-backend (#8593)

## Summary

Closes #8568

Author: j178

crates/uv-cli/src/lib.rs

@@ -2473,7 +2473,7 @@ pub struct InitArgs {
     ///
     /// Defines a `[build-system]` for the project.
     ///
-    /// This is the default behavior when using `--lib`.
+    /// This is the default behavior when using `--lib` or `--build-backend`.
     ///
     /// When using `--app`, this will include a `[project.scripts]` entrypoint and use a `src/`
     /// project structure.
@@ -2485,7 +2485,7 @@ pub struct InitArgs {
     /// Does not include a `[build-system]` for the project.
     ///
     /// This is the default behavior when using `--app`.
-    #[arg(long, overrides_with = "package", conflicts_with = "lib")]
+    #[arg(long, overrides_with = "package", conflicts_with_all = ["lib", "build_backend"])]
     pub r#no_package: bool,
 
     /// Create a project for an application.
@@ -2515,7 +2515,7 @@ pub struct InitArgs {
     ///
     /// By default, adds a requirement on the system Python version; use `--python` to specify an
     /// alternative Python version requirement.
-    #[arg(long, alias="script", conflicts_with_all=["app", "lib", "package"])]
+    #[arg(long, alias="script", conflicts_with_all=["app", "lib", "package", "build_backend"])]
     pub r#script: bool,
 
     /// Initialize a version control system for the project.
@@ -2526,6 +2526,8 @@ pub struct InitArgs {
     pub vcs: Option<VersionControlSystem>,
 
     /// Initialize a build-backend of choice for the project.
+    ///
+    /// Implicitly sets `--package`.
     #[arg(long, value_enum, conflicts_with_all=["script", "no_package"])]
     pub build_backend: Option<ProjectBuildBackend>,
 

crates/uv/src/settings.rs

@@ -202,7 +202,8 @@ impl InitSettings {
             (_, _, _) => unreachable!("`app`, `lib`, and `script` are mutually exclusive"),
         };
 
-        let package = flag(package || r#virtual, no_package).unwrap_or(kind.packaged_by_default());
+        let package = flag(package || build_backend.is_some() || r#virtual, no_package)
+            .unwrap_or(kind.packaged_by_default());
 
         Self {
             path,

crates/uv/tests/it/init.rs

@@ -2536,6 +2536,45 @@ fn init_library_flit() -> Result<()> {
     Ok(())
 }
 
+/// Run `uv init --build-backend flit` should be equivalent to `uv init --package --build-backend flit`.
+#[test]
+fn init_backend_implies_package() {
+    let context = TestContext::new("3.12");
+
+    uv_snapshot!(context.filters(), context.init().arg("project").arg("--build-backend").arg("flit"), @r#"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Initialized project `project` at `[TEMP_DIR]/project`
+    "#);
+
+    let pyproject = context.read("project/pyproject.toml");
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject, @r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        description = "Add your description here"
+        readme = "README.md"
+        requires-python = ">=3.12"
+        dependencies = []
+
+        [project.scripts]
+        project = "project:main"
+
+        [build-system]
+        requires = ["flit_core>=3.2,<4"]
+        build-backend = "flit_core.buildapi"
+        "#
+        );
+    });
+}
+
 /// Run `uv init --app --package --build-backend maturin` to create a packaged application project
 #[test]
 #[cfg(feature = "crates-io")]

docs/reference/cli.md

@@ -489,7 +489,9 @@ uv init [OPTIONS] [PATH]
 
 <li><code>none</code>:  Do not infer the author information</li>
 </ul>
-</dd><dt><code>--build-backend</code> <i>build-backend</i></dt><dd><p>Initialize a build-backend of choice for the project</p>
+</dd><dt><code>--build-backend</code> <i>build-backend</i></dt><dd><p>Initialize a build-backend of choice for the project.</p>
+
+<p>Implicitly sets <code>--package</code>.</p>
 
 <p>Possible values:</p>
 
@@ -589,7 +591,7 @@ uv init [OPTIONS] [PATH]
 
 <p>Defines a <code>[build-system]</code> for the project.</p>
 
-<p>This is the default behavior when using <code>--lib</code>.</p>
+<p>This is the default behavior when using <code>--lib</code> or <code>--build-backend</code>.</p>
 
 <p>When using <code>--app</code>, this will include a <code>[project.scripts]</code> entrypoint and use a <code>src/</code> project structure.</p>