Allow `[project]` to be missing from a `pyproject.toml` (#14113)

Closes #8666 
Closes https://github.com/astral-sh/uv/issues/6838

---------

Co-authored-by: Zanie Blue <contact@zanie.dev>

crates/uv-distribution/src/metadata/dependency_groups.rs

@@ -77,6 +77,7 @@ impl SourcedDependencyGroups {
                 SourceStrategy::Enabled => MemberDiscovery::default(),
                 SourceStrategy::Disabled => MemberDiscovery::None,
             },
+            ..DiscoveryOptions::default()
         };
 
         // The subsequent API takes an absolute path to the dir the pyproject is in
@@ -84,7 +85,7 @@ impl SourcedDependencyGroups {
         let absolute_pyproject_path =
             std::path::absolute(pyproject_path).map_err(WorkspaceError::Normalize)?;
         let project_dir = absolute_pyproject_path.parent().unwrap_or(&empty);
-        let project = VirtualProject::discover_defaulted(project_dir, &discovery, cache).await?;
+        let project = VirtualProject::discover(project_dir, &discovery, cache).await?;
 
         // Collect the dependency groups.
         let dependency_groups =

crates/uv-distribution/src/metadata/requires_dist.rs

@@ -61,6 +61,7 @@ impl RequiresDist {
                 SourceStrategy::Enabled => MemberDiscovery::default(),
                 SourceStrategy::Disabled => MemberDiscovery::None,
             },
+            ..DiscoveryOptions::default()
         };
         let Some(project_workspace) =
             ProjectWorkspace::from_maybe_project_root(install_path, &discovery, cache).await?

crates/uv-workspace/src/lib.rs

@@ -1,6 +1,7 @@
 pub use workspace::{
-    DiscoveryOptions, Editability, MemberDiscovery, ProjectWorkspace, RequiresPythonSources,
+    DiscoveryOptions, Editability, MemberDiscovery, ProjectDiscovery, ProjectWorkspace,
-    VirtualProject, Workspace, WorkspaceCache, WorkspaceError, WorkspaceMember,
+    RequiresPythonSources, VirtualProject, Workspace, WorkspaceCache, WorkspaceError,
+    WorkspaceMember,
 };
 
 pub mod dependency_groups;

crates/uv-workspace/src/workspace.rs

@@ -94,12 +94,51 @@ pub enum MemberDiscovery {
     Ignore(BTreeSet<PathBuf>),
 }
 
+/// Whether a "project" must be defined via a `[project]` table.
+#[derive(Debug, Default, Clone, Hash, PartialEq, Eq)]
+pub enum ProjectDiscovery {
+    /// The `[project]` table is optional; when missing, the target is treated as virtual.
+    #[default]
+    Optional,
+    /// A `[project]` table must be defined, unless `[tool.uv.workspace]` is present indicating a
+    /// legacy non-project workspace root.
+    ///
+    /// If neither is defined, discovery will fail.
+    Legacy,
+    /// A `[project]` table must be defined.
+    ///
+    /// If not defined, discovery will fail.
+    Required,
+}
+
+impl ProjectDiscovery {
+    /// Whether a `[project]` table is required.
+    pub fn allows_implicit_workspace(&self) -> bool {
+        match self {
+            Self::Optional => true,
+            Self::Legacy => false,
+            Self::Required => false,
+        }
+    }
+
+    /// Whether a legacy workspace root is allowed.
+    pub fn allows_legacy_workspace(&self) -> bool {
+        match self {
+            Self::Optional => true,
+            Self::Legacy => true,
+            Self::Required => false,
+        }
+    }
+}
+
 #[derive(Debug, Default, Clone, Hash, PartialEq, Eq)]
 pub struct DiscoveryOptions {
     /// The path to stop discovery at.
     pub stop_discovery_at: Option<PathBuf>,
     /// The strategy to use when discovering workspace members.
     pub members: MemberDiscovery,
+    /// The strategy to use when discovering the project.
+    pub project: ProjectDiscovery,
 }
 
 pub type RequiresPythonSources = BTreeMap<(PackageName, Option<GroupName>), VersionSpecifiers>;
@@ -1561,13 +1600,13 @@ fn is_included_in_workspace(
 
 /// A project that can be discovered.
 ///
-/// The project could be a package within a workspace, a real workspace root, or a (legacy)
+/// The project could be a package within a workspace, a real workspace root, or a non-project
-/// non-project workspace root, which can define its own dev dependencies.
+/// workspace root, which can define its own dev dependencies.
 #[derive(Debug, Clone)]
 pub enum VirtualProject {
     /// A project (which could be a workspace root or member).
     Project(ProjectWorkspace),
-    /// A (legacy) non-project workspace root.
+    /// A non-project workspace root.
     NonProject(Workspace),
 }
 
@@ -1583,33 +1622,6 @@ impl VirtualProject {
         path: &Path,
         options: &DiscoveryOptions,
         cache: &WorkspaceCache,
-    ) -> Result<Self, WorkspaceError> {
-        Self::discover_impl(path, options, cache, false).await
-    }
-
-    /// Equivalent to [`VirtualProject::discover`] but consider it acceptable for
-    /// both `[project]` and `[tool.uv.workspace]` to be missing.
-    ///
-    /// If they are, we act as if an empty `[tool.uv.workspace]` was found.
-    pub async fn discover_defaulted(
-        path: &Path,
-        options: &DiscoveryOptions,
-        cache: &WorkspaceCache,
-    ) -> Result<Self, WorkspaceError> {
-        Self::discover_impl(path, options, cache, true).await
-    }
-
-    /// Find the current project or virtual workspace root, given the current directory.
-    ///
-    /// Similar to calling [`ProjectWorkspace::discover`] with a fallback to [`Workspace::discover`],
-    /// but avoids rereading the `pyproject.toml` (and relying on error-handling as control flow).
-    ///
-    /// This method requires an absolute path and panics otherwise.
-    async fn discover_impl(
-        path: &Path,
-        options: &DiscoveryOptions,
-        cache: &WorkspaceCache,
-        default_missing_workspace: bool,
     ) -> Result<Self, WorkspaceError> {
         assert!(
             path.is_absolute(),
@@ -1656,6 +1668,7 @@ impl VirtualProject {
             .as_ref()
             .and_then(|tool| tool.uv.as_ref())
             .and_then(|uv| uv.workspace.as_ref())
+            .filter(|_| options.project.allows_legacy_workspace())
         {
             // Otherwise, if it contains a `tool.uv.workspace` table, it's a non-project workspace
             // root.
@@ -1674,7 +1687,7 @@ impl VirtualProject {
             .await?;
 
             Ok(Self::NonProject(workspace))
-        } else if default_missing_workspace {
+        } else if options.project.allows_implicit_workspace() {
             // Otherwise it's a pyproject.toml that maybe contains dependency-groups
             // that we want to treat like a project/workspace to handle those uniformly
             let project_path = std::path::absolute(project_root)

crates/uv/src/commands/project/version.rs

@@ -358,7 +358,10 @@ async fn find_target(
         VirtualProject::Project(
             Workspace::discover(
                 project_dir,
-                &DiscoveryOptions::default(),
+                &DiscoveryOptions {
+                    project: uv_workspace::ProjectDiscovery::Required,
+                    ..DiscoveryOptions::default()
+                },
                 &WorkspaceCache::default(),
             )
             .await
@@ -369,7 +372,10 @@ async fn find_target(
     } else {
         VirtualProject::discover(
             project_dir,
-            &DiscoveryOptions::default(),
+            &DiscoveryOptions {
+                project: uv_workspace::ProjectDiscovery::Required,
+                ..DiscoveryOptions::default()
+            },
             &WorkspaceCache::default(),
         )
         .await

crates/uv/tests/it/edit.rs

@@ -4795,6 +4795,306 @@ fn add_non_project() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn add_virtual_empty() -> Result<()> {
+    // testing how `uv add` reacts to a pyproject with no `[project]` and nothing useful to it
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+    "#})?;
+
+    // Add normal dep (doesn't make sense)
+    uv_snapshot!(context.filters(), context.add()
+        .arg("sortedcontainers"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Project is missing a `[project]` table; add a `[project]` table to use production dependencies, or run `uv add --dev` instead
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+        "#
+        );
+    });
+
+    // Add dependency-group (can make sense!)
+    uv_snapshot!(context.filters(), context.add()
+        .arg("sortedcontainers")
+        .arg("--group").arg("dev"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 1 package in [TIME]
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + sortedcontainers==2.4.0
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+
+        [dependency-groups]
+        dev = [
+            "sortedcontainers>=2.4.0",
+        ]
+        "#
+        );
+    });
+
+    Ok(())
+}
+
+#[test]
+fn add_virtual_dependency_group() -> Result<()> {
+    // testing basic `uv add --group` functionality
+    // when the pyproject.toml is fully virtual (no `[project]`)
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+    "#})?;
+
+    // Add to existing group
+    uv_snapshot!(context.filters(), context.add()
+        .arg("sortedcontainers")
+        .arg("--group").arg("dev"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 3 packages in [TIME]
+    Prepared 2 packages in [TIME]
+    Installed 2 packages in [TIME]
+     + sniffio==1.3.1
+     + sortedcontainers==2.4.0
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = [
+            "sniffio",
+            "sortedcontainers>=2.4.0",
+        ]
+        "#
+        );
+    });
+
+    // Add to new group
+    uv_snapshot!(context.filters(), context.add()
+        .arg("sortedcontainers")
+        .arg("--group").arg("baz"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 3 packages in [TIME]
+    Audited 2 packages in [TIME]
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = [
+            "sniffio",
+            "sortedcontainers>=2.4.0",
+        ]
+        baz = [
+            "sortedcontainers>=2.4.0",
+        ]
+        "#
+        );
+    });
+
+    Ok(())
+}
+
+#[test]
+fn remove_virtual_empty() -> Result<()> {
+    // testing how `uv remove` reacts to a pyproject with no `[project]` and nothing useful to it
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+
+        "#,
+    )?;
+
+    // Remove normal dep (doesn't make sense)
+    uv_snapshot!(context.filters(), context.remove()
+        .arg("sortedcontainers"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: The dependency `sortedcontainers` could not be found in `project.dependencies`
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+        "#
+        );
+    });
+
+    // Remove dependency-group (can make sense, but nothing there!)
+    uv_snapshot!(context.filters(), context.remove()
+        .arg("sortedcontainers")
+        .arg("--group").arg("dev"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: The dependency `sortedcontainers` could not be found in `tool.uv.dev-dependencies` or `tool.uv.dependency-groups.dev`
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+        "#
+        );
+    });
+
+    Ok(())
+}
+
+#[test]
+fn remove_virtual_dependency_group() -> Result<()> {
+    // testing basic `uv remove --group` functionality
+    // when the pyproject.toml is fully virtual (no `[project]`)
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+    "#})?;
+
+    // Remove from group
+    uv_snapshot!(context.filters(), context.remove()
+        .arg("sortedcontainers")
+        .arg("--group").arg("foo"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 2 packages in [TIME]
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + sniffio==1.3.1
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [dependency-groups]
+        foo = []
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+        "#
+        );
+    });
+
+    // Remove from non-existent group
+    uv_snapshot!(context.filters(), context.remove()
+        .arg("sortedcontainers")
+        .arg("--group").arg("baz"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: The dependency `sortedcontainers` could not be found in `dependency-groups.baz`
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [dependency-groups]
+        foo = []
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+        "#
+        );
+    });
+
+    Ok(())
+}
+
 /// Add the same requirement multiple times.
 #[test]
 fn add_repeat() -> Result<()> {

crates/uv/tests/it/export.rs

@@ -1145,6 +1145,102 @@ fn requirements_txt_non_project() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn virtual_empty() -> Result<()> {
+    // testing how `uv export` reacts to a pyproject with no `[project]` and nothing useful to it
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+    "#})?;
+
+    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]
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved in [TIME]
+    ");
+
+    Ok(())
+}
+
+#[test]
+fn virtual_dependency_group() -> Result<()> {
+    // testing basic `uv export --group` functionality
+    // when the pyproject.toml is fully virtual (no `[project]`)
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+    "#})?;
+
+    // default groups
+    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]
+    sniffio==1.3.1 \
+        --hash=sha256:2f6da418d1f1e0fddd844478f41680e794e6051915791a034ff65e5f100525a2 \
+        --hash=sha256:f4324edc670a0f49750a81b895f35c3adb843cca46f0530f79fc1babb23789dc
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 3 packages in [TIME]
+    ");
+
+    // explicit --group
+    uv_snapshot!(context.filters(), context.export()
+        .arg("--group").arg("bar"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv export --cache-dir [CACHE_DIR] --group bar
+    iniconfig==2.0.0 \
+        --hash=sha256:2d91e135bf72d31a410b17c16da610a82cb55f6b0477d1a902134b24a455b8b3 \
+        --hash=sha256:b6a85871a79d2e3b22d2d1b94ac2824226a63c6b741c88f7ae975f18b6778374
+    sniffio==1.3.1 \
+        --hash=sha256:2f6da418d1f1e0fddd844478f41680e794e6051915791a034ff65e5f100525a2 \
+        --hash=sha256:f4324edc670a0f49750a81b895f35c3adb843cca46f0530f79fc1babb23789dc
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 3 packages in [TIME]
+    ");
+
+    // explicit --only-group
+    uv_snapshot!(context.filters(), context.export()
+        .arg("--only-group").arg("foo"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv export --cache-dir [CACHE_DIR] --only-group foo
+    sortedcontainers==2.4.0 \
+        --hash=sha256:25caa5a06cc30b6b83d11423433f65d1f9d76c4c6a0c90e3379eaa43b9bfdb88 \
+        --hash=sha256:a163dcaede0f1c021485e957a39245190e74249897e2ae4b2aa38595db237ee0
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 3 packages in [TIME]
+    ");
+
+    Ok(())
+}
+
 #[cfg(feature = "git")]
 #[test]
 fn requirements_txt_https_git_credentials() -> Result<()> {

crates/uv/tests/it/python_find.rs

@@ -413,6 +413,180 @@ fn python_find_project() {
     ");
 }
 
+#[test]
+fn virtual_empty() {
+    // testing how `uv python find` reacts to a pyproject with no `[project]` and nothing useful to it
+    let context = TestContext::new_with_versions(&["3.10", "3.11", "3.12"]);
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml
+        .write_str(indoc! {r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+    "#})
+        .unwrap();
+
+    // Ask for the python
+    uv_snapshot!(context.filters(), context.python_find(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.10]
+
+    ----- stderr -----
+    ");
+
+    // Ask for the python (--no-project)
+    uv_snapshot!(context.filters(), context.python_find()
+        .arg("--no-project"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.10]
+
+    ----- stderr -----
+    ");
+
+    // Ask for specific python (3.11)
+    uv_snapshot!(context.filters(), context.python_find().arg("3.11"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    ");
+
+    // Create a pin
+    uv_snapshot!(context.filters(), context.python_pin().arg("3.12"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Pinned `.python-version` to `3.12`
+
+    ----- stderr -----
+    "###);
+
+    // Ask for the python
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.12]
+
+    ----- stderr -----
+    "###);
+
+    // Ask for specific python (3.11)
+    uv_snapshot!(context.filters(), context.python_find().arg("3.11"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    ");
+
+    // Ask for the python (--no-project)
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.12]
+
+    ----- stderr -----
+    "###);
+}
+
+#[test]
+fn virtual_dependency_group() {
+    // testing basic `uv python find` functionality
+    // when the pyproject.toml is fully virtual (no `[project]`, but `[dependency-groups]` defined,
+    // which really shouldn't matter)
+    let context = TestContext::new_with_versions(&["3.10", "3.11", "3.12"]);
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml
+        .write_str(indoc! {r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+    "#})
+        .unwrap();
+
+    // Ask for the python
+    uv_snapshot!(context.filters(), context.python_find(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.10]
+
+    ----- stderr -----
+    ");
+
+    // Ask for the python (--no-project)
+    uv_snapshot!(context.filters(), context.python_find()
+        .arg("--no-project"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.10]
+
+    ----- stderr -----
+    ");
+
+    // Ask for specific python (3.11)
+    uv_snapshot!(context.filters(), context.python_find().arg("3.11"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    ");
+
+    // Create a pin
+    uv_snapshot!(context.filters(), context.python_pin().arg("3.12"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Pinned `.python-version` to `3.12`
+
+    ----- stderr -----
+    "###);
+
+    // Ask for the python
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.12]
+
+    ----- stderr -----
+    "###);
+
+    // Ask for specific python (3.11)
+    uv_snapshot!(context.filters(), context.python_find().arg("3.11"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    ");
+
+    // Ask for the python (--no-project)
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.12]
+
+    ----- stderr -----
+    "###);
+}
+
 #[test]
 fn python_find_venv() {
     let context: TestContext = TestContext::new_with_versions(&["3.11", "3.12"])

crates/uv/tests/it/run.rs

@@ -3313,9 +3313,9 @@ fn run_module_stdin() {
     "###);
 }
 
-/// When the `pyproject.toml` file is invalid.
+/// Test for how run reacts to a pyproject.toml without a `[project]`
 #[test]
-fn run_project_toml_error() -> Result<()> {
+fn virtual_empty() -> Result<()> {
     let context = TestContext::new("3.12")
         .with_filtered_python_names()
         .with_filtered_virtualenv_bin()
@@ -3331,26 +3331,29 @@ fn run_project_toml_error() -> Result<()> {
     let init = src.child("__init__.py");
     init.touch()?;
 
-    // `run` should fail
+    // `run` should work fine
     uv_snapshot!(context.filters(), context.run().arg("python").arg("-c").arg("import sys; print(sys.executable)"), @r"
-    success: false
-    exit_code: 2
-    ----- stdout -----
-
-    ----- stderr -----
-    error: No `project` table found in: `[TEMP_DIR]/pyproject.toml`
-    ");
-
-    // `run --no-project` should not
-    uv_snapshot!(context.filters(), context.run().arg("--no-project").arg("python").arg("-c").arg("import sys; print(sys.executable)"), @r"
     success: true
     exit_code: 0
     ----- stdout -----
     [VENV]/[BIN]/[PYTHON]
 
     ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved in [TIME]
+    Audited in [TIME]
     ");
 
+    // `run --no-project` should also work fine
+    uv_snapshot!(context.filters(), context.run().arg("--no-project").arg("python").arg("-c").arg("import sys; print(sys.executable)"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [VENV]/[BIN]/[PYTHON]
+
+    ----- stderr -----
+    "###);
+
     Ok(())
 }
 

crates/uv/tests/it/sync.rs

@@ -5616,6 +5616,95 @@ fn virtual_no_build() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn virtual_empty() -> Result<()> {
+    // testing how `uv sync` reacts to a pyproject with no `[project]` and nothing useful to it
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+    "#})?;
+
+    uv_snapshot!(context.filters(), context.sync(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved in [TIME]
+    Audited in [TIME]
+    ");
+
+    Ok(())
+}
+
+#[test]
+fn virtual_dependency_group() -> Result<()> {
+    // testing basic `uv sync --group` functionality
+    // when the pyproject.toml is fully virtual (no `[project]`)
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+    "#})?;
+
+    // default groups
+    uv_snapshot!(context.filters(), context.sync(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 3 packages in [TIME]
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + sniffio==1.3.1
+    ");
+
+    // explicit --group
+    uv_snapshot!(context.filters(), context.sync()
+        .arg("--group").arg("bar"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 3 packages in [TIME]
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + iniconfig==2.0.0
+    ");
+
+    // explicit --only-group
+    uv_snapshot!(context.filters(), context.sync()
+        .arg("--only-group").arg("foo"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: No `requires-python` value found in the workspace. Defaulting to `>=3.12`.
+    Resolved 3 packages in [TIME]
+    Prepared 1 package in [TIME]
+    Uninstalled 2 packages in [TIME]
+    Installed 1 package in [TIME]
+     - iniconfig==2.0.0
+     - sniffio==1.3.1
+     + sortedcontainers==2.4.0
+    ");
+
+    Ok(())
+}
+
 #[test]
 fn virtual_no_build_dynamic_cached() -> Result<()> {
     let context = TestContext::new("3.12");

crates/uv/tests/it/venv.rs

@@ -210,6 +210,61 @@ fn create_venv_project_environment() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn virtual_empty() -> Result<()> {
+    // testing how `uv venv` reacts to a pyproject with no `[project]` and nothing useful to it
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+    "#})?;
+
+    uv_snapshot!(context.filters(), context.venv(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
+    Creating virtual environment at: .venv
+    warning: A virtual environment already exists at `.venv`. In the future, uv will require `--clear` to replace it
+    Activate with: source .venv/[BIN]/activate
+    ");
+
+    Ok(())
+}
+
+#[test]
+fn virtual_dependency_group() -> Result<()> {
+    // testing basic `uv venv` functionality
+    // when the pyproject.toml is fully virtual (no `[project]`, but `[dependency-groups]` defined)
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+    "#})?;
+
+    uv_snapshot!(context.filters(), context.venv(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
+    Creating virtual environment at: .venv
+    warning: A virtual environment already exists at `.venv`. In the future, uv will require `--clear` to replace it
+    Activate with: source .venv/[BIN]/activate
+    ");
+
+    Ok(())
+}
+
 #[test]
 fn create_venv_defaults_to_cwd() {
     let context = TestContext::new_with_versions(&["3.12"]);

crates/uv/tests/it/version.rs

@@ -1867,7 +1867,7 @@ fn version_get_workspace() -> Result<()> {
     ----- stdout -----
 
     ----- stderr -----
-    error: Missing `project.name` field in: pyproject.toml
+    error: No `project` table found in: `[TEMP_DIR]/pyproject.toml`
     ");
 
     Ok(())
@@ -2462,6 +2462,137 @@ fn version_set_evil_constraints() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn virtual_empty() -> Result<()> {
+    // testing how `uv version` reacts to a pyproject with no `[project]` and nothing useful to it
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+    "#})?;
+
+    // Get version (doesn't make sense)
+    uv_snapshot!(context.filters(), context.version()
+        .arg("sortedcontainers"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: No `project` table found in: `[TEMP_DIR]/pyproject.toml`
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+        "#
+        );
+    });
+
+    // Set version (can make sense, but we should still refuse?)
+    uv_snapshot!(context.filters(), context.version()
+        .arg("1.0.0"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: No `project` table found in: `[TEMP_DIR]/pyproject.toml`
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [tool.mycooltool]
+        wow = "someconfig"
+        "#
+        );
+    });
+
+    Ok(())
+}
+
+#[test]
+fn add_virtual_dependency_group() -> Result<()> {
+    // testing basic `uv version` functionality
+    // when the pyproject.toml is fully virtual (no `[project]`)
+    // But at least has some dependency-group tables (shouldn't matter to this command)
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+    "#})?;
+
+    // Get the version (doesn't make sense)
+    uv_snapshot!(context.filters(), context.version(), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: No `project` table found in: `[TEMP_DIR]/pyproject.toml`
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+        "#
+        );
+    });
+
+    // Set the version (can make sense, we should refuse?)
+    uv_snapshot!(context.filters(), context.version()
+        .arg("1.0.0"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: No `project` table found in: `[TEMP_DIR]/pyproject.toml`
+    ");
+
+    let pyproject_toml = context.read("pyproject.toml");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r#"
+        [dependency-groups]
+        foo = ["sortedcontainers"]
+        bar = ["iniconfig"]
+        dev = ["sniffio"]
+        "#
+        );
+    });
+
+    Ok(())
+}
+
 /// Bump the version with conflicting extras, to ensure we're activating the correct subset of
 /// extras during the resolve.
 #[test]