Do not require workspace members to sync with --frozen (#6737)

## Summary

Closes https://github.com/astral-sh/uv/issues/6685.

Cargo.lock

@@ -4743,7 +4743,6 @@ dependencies = [
  "uv-auth",
  "uv-cache",
  "uv-normalize",
- "uv-workspace",
 ]
 
 [[package]]

crates/uv-configuration/Cargo.toml

@@ -20,7 +20,6 @@ pypi-types = { workspace = true }
 uv-auth = { workspace = true }
 uv-cache = { workspace = true }
 uv-normalize = { workspace = true }
-uv-workspace = { workspace = true }
 
 clap = { workspace = true, features = ["derive"], optional = true }
 either = { workspace = true }

crates/uv-configuration/src/install_options.rs

@@ -1,9 +1,10 @@
+use std::collections::BTreeSet;
+
 use rustc_hash::FxHashSet;
 use tracing::debug;
 
 use distribution_types::{Name, Resolution};
 use pep508_rs::PackageName;
-use uv_workspace::VirtualProject;
 
 #[derive(Debug, Clone, Default)]
 pub struct InstallOptions {
@@ -28,13 +29,14 @@ impl InstallOptions {
     pub fn filter_resolution(
         &self,
         resolution: Resolution,
-        project: &VirtualProject,
+        project_name: Option<&PackageName>,
+        members: &BTreeSet<PackageName>,
     ) -> Resolution {
         // If `--no-install-project` is set, remove the project itself.
-        let resolution = self.apply_no_install_project(resolution, project);
+        let resolution = self.apply_no_install_project(resolution, project_name);
 
         // If `--no-install-workspace` is set, remove the project and any workspace members.
-        let resolution = self.apply_no_install_workspace(resolution, project);
+        let resolution = self.apply_no_install_workspace(resolution, members);
 
         // If `--no-install-package` is provided, remove the requested packages.
         self.apply_no_install_package(resolution)
@@ -43,13 +45,13 @@ impl InstallOptions {
     fn apply_no_install_project(
         &self,
         resolution: Resolution,
-        project: &VirtualProject,
+        project_name: Option<&PackageName>,
     ) -> Resolution {
         if !self.no_install_project {
             return resolution;
         }
 
-        let Some(project_name) = project.project_name() else {
+        let Some(project_name) = project_name else {
             debug!("Ignoring `--no-install-project` for virtual workspace");
             return resolution;
         };
@@ -60,17 +62,13 @@ impl InstallOptions {
     fn apply_no_install_workspace(
         &self,
         resolution: Resolution,
-        project: &VirtualProject,
+        members: &BTreeSet<PackageName>,
     ) -> Resolution {
         if !self.no_install_workspace {
             return resolution;
         }
 
-        let workspace_packages = project.workspace().packages();
-        resolution.filter(|dist| {
-            !workspace_packages.contains_key(dist.name())
-                && Some(dist.name()) != project.project_name()
-        })
+        resolution.filter(|dist| !members.contains(dist.name()))
     }
 
     fn apply_no_install_package(&self, resolution: Resolution) -> Resolution {

crates/uv-resolver/src/lock.rs

@@ -409,6 +409,11 @@ impl Lock {
         &self.supported_environments
     }
 
+    /// Returns the workspace members that were used to generate this lock.
+    pub fn members(&self) -> &BTreeSet<PackageName> {
+        &self.manifest.members
+    }
+
     /// If this lockfile was built from a forking resolution with non-identical forks, return the
     /// markers of those forks, otherwise `None`.
     pub fn fork_markers(&self) -> &[MarkerTree] {

crates/uv-workspace/src/lib.rs

@@ -1,6 +1,6 @@
 pub use workspace::{
-    check_nested_workspaces, DiscoveryOptions, ProjectWorkspace, VirtualProject, Workspace,
-    WorkspaceError, WorkspaceMember,
+    check_nested_workspaces, DiscoveryOptions, MemberDiscovery, ProjectWorkspace, VirtualProject,
+    Workspace, WorkspaceError, WorkspaceMember,
 };
 
 pub mod pyproject;

crates/uv-workspace/src/workspace.rs

@@ -44,12 +44,23 @@ pub enum WorkspaceError {
     Normalize(#[source] std::io::Error),
 }
 
+#[derive(Debug, Default, Clone)]
+pub enum MemberDiscovery<'a> {
+    /// Discover all workspace members.
+    #[default]
+    All,
+    /// Don't discover any workspace members.
+    None,
+    /// Discover workspace members, but ignore the given paths.
+    Ignore(FxHashSet<&'a Path>),
+}
+
 #[derive(Debug, Default, Clone)]
 pub struct DiscoveryOptions<'a> {
     /// The path to stop discovery at.
     pub stop_discovery_at: Option<&'a Path>,
-    /// The set of member paths to ignore.
-    pub ignore: FxHashSet<&'a Path>,
+    /// The strategy to use when discovering workspace members.
+    pub members: MemberDiscovery<'a>,
 }
 
 /// A workspace, consisting of a root directory and members. See [`ProjectWorkspace`].
@@ -546,7 +557,12 @@ impl Workspace {
                     .clone();
 
                 // If the directory is explicitly ignored, skip it.
-                if options.ignore.contains(member_root.as_path()) {
+                let skip = match &options.members {
+                    MemberDiscovery::All => false,
+                    MemberDiscovery::None => true,
+                    MemberDiscovery::Ignore(ignore) => ignore.contains(member_root.as_path()),
+                };
+                if skip {
                     debug!(
                         "Ignoring workspace member: `{}`",
                         member_root.simplified_display()

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

@@ -15,7 +15,7 @@ use uv_python::{
 };
 use uv_resolver::RequiresPython;
 use uv_workspace::pyproject_mut::{DependencyTarget, PyProjectTomlMut};
-use uv_workspace::{DiscoveryOptions, Workspace, WorkspaceError};
+use uv_workspace::{DiscoveryOptions, MemberDiscovery, Workspace, WorkspaceError};
 
 use crate::commands::project::find_requires_python;
 use crate::commands::reporters::PythonDownloadReporter;
@@ -141,7 +141,7 @@ async fn init_project(
         match Workspace::discover(
             parent,
             &DiscoveryOptions {
-                ignore: std::iter::once(path).collect(),
+                members: MemberDiscovery::Ignore(std::iter::once(path).collect()),
                 ..DiscoveryOptions::default()
             },
         )

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

@@ -1,7 +1,6 @@
 use anyhow::{Context, Result};
-use itertools::Itertools;
-
 use distribution_types::{Dist, ResolvedDist, SourceDist};
+use itertools::Itertools;
 use pep508_rs::MarkerTree;
 use uv_auth::store_credentials_from_url;
 use uv_cache::Cache;
@@ -14,7 +13,7 @@ use uv_normalize::{PackageName, DEV_DEPENDENCIES};
 use uv_python::{PythonDownloads, PythonEnvironment, PythonPreference, PythonRequest};
 use uv_resolver::{FlatIndex, Lock};
 use uv_types::{BuildIsolation, HashStrategy};
-use uv_workspace::{DiscoveryOptions, VirtualProject, Workspace};
+use uv_workspace::{DiscoveryOptions, MemberDiscovery, VirtualProject, Workspace};
 
 use crate::commands::pip::loggers::{DefaultInstallLogger, DefaultResolveLogger, InstallLogger};
 use crate::commands::pip::operations::Modifications;
@@ -52,6 +51,15 @@ pub(crate) async fn sync(
                 .with_current_project(package.clone())
                 .with_context(|| format!("Package `{package}` not found in workspace"))?,
         )
+    } else if frozen {
+        VirtualProject::discover(
+            &CWD,
+            &DiscoveryOptions {
+                members: MemberDiscovery::None,
+                ..DiscoveryOptions::default()
+            },
+        )
+        .await?
     } else {
         VirtualProject::discover(&CWD, &DiscoveryOptions::default()).await?
     };
@@ -201,7 +209,8 @@ pub(super) async fn do_sync(
     let resolution = apply_no_virtual_project(resolution);
 
     // Filter resolution based on install-specific options.
-    let resolution = install_options.filter_resolution(resolution, project);
+    let resolution =
+        install_options.filter_resolution(resolution, project.project_name(), lock.members());
 
     // Add all authenticated sources to the cache.
     for url in index_locations.urls() {

crates/uv/tests/sync.rs

@@ -1103,10 +1103,30 @@ fn no_install_workspace() -> Result<()> {
      + sniffio==1.3.1
     "###);
 
-    // However, we do require the `pyproject.toml`.
+    // Remove the virtual environment.
+    fs_err::remove_dir_all(&context.venv)?;
+
+    // We don't require the `pyproject.toml` for non-root members, if `--frozen` is provided.
     fs_err::remove_file(child.join("pyproject.toml"))?;
 
-    uv_snapshot!(context.filters(), context.sync().arg("--no-install-workspace"), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--no-install-workspace").arg("--frozen"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Using Python 3.12.[X] interpreter at: [PYTHON-3.12]
+    Creating virtualenv at: .venv
+    Prepared 4 packages in [TIME]
+    Installed 4 packages in [TIME]
+     + anyio==3.7.0
+     + idna==3.6
+     + iniconfig==2.0.0
+     + sniffio==1.3.1
+    "###);
+
+    // Unless `--package` is used.
+    uv_snapshot!(context.filters(), context.sync().arg("--package").arg("child").arg("--no-install-workspace").arg("--frozen"), @r###"
     success: false
     exit_code: 2
     ----- stdout -----
@@ -1115,6 +1135,18 @@ fn no_install_workspace() -> Result<()> {
     error: Workspace member `[TEMP_DIR]/child` is missing a `pyproject.toml` (matches: `child`)
     "###);
 
+    // But we do require the root `pyproject.toml`.
+    fs_err::remove_file(context.temp_dir.join("pyproject.toml"))?;
+
+    uv_snapshot!(context.filters(), context.sync().arg("--no-install-workspace").arg("--frozen"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: No `pyproject.toml` found in current directory or any parent directory
+    "###);
+
     Ok(())
 }