Allow virtual packages with --no-build (#12314)

## Summary

Closes #12311.

crates/uv-distribution-types/src/lib.rs

@@ -639,6 +639,7 @@ impl SourceDist {
         }
     }
 
+    /// Returns the [`Version`] of the distribution, if it is known.
     pub fn version(&self) -> Option<&Version> {
         match self {
             Self::Registry(source_dist) => Some(&source_dist.version),
@@ -646,7 +647,7 @@ impl SourceDist {
         }
     }
 
-    /// Return true if the distribution is editable.
+    /// Returns `true` if the distribution is editable.
     pub fn is_editable(&self) -> bool {
         match self {
             Self::Directory(DirectorySourceDist { editable, .. }) => *editable,
@@ -654,7 +655,15 @@ impl SourceDist {
         }
     }
 
-    /// Return true if the distribution refers to a local file or directory.
+    /// Returns `true` if the distribution is virtual.
+    pub fn is_virtual(&self) -> bool {
+        match self {
+            Self::Directory(DirectorySourceDist { r#virtual, .. }) => *r#virtual,
+            _ => false,
+        }
+    }
+
+    /// Returns `true` if the distribution refers to a local file or directory.
     pub fn is_local(&self) -> bool {
         matches!(self, Self::Directory(_) | Self::Path(_))
     }
@@ -668,7 +677,7 @@ impl SourceDist {
         }
     }
 
-    /// Return the source tree of the distribution, if available.
+    /// Returns the source tree of the distribution, if available.
     pub fn source_tree(&self) -> Option<&Path> {
         match self {
             Self::Directory(dist) => Some(&dist.install_path),

crates/uv-resolver/src/lock/mod.rs

@@ -2196,8 +2196,11 @@ impl Package {
             };
         }
 
-        if !no_build {
         if let Some(sdist) = self.to_source_dist(workspace_root)? {
+            // Even with `--no-build`, allow virtual packages. (In the future, we may want to allow
+            // any local source tree, or at least editable source trees, which we allow in
+            // `uv pip`.)
+            if !no_build || sdist.is_virtual() {
                 return Ok(Dist::Source(sdist));
             }
         }

crates/uv/tests/it/lock.rs

@@ -23005,14 +23005,16 @@ fn lock_no_build_static_metadata() -> Result<()> {
     "###);
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync().arg("--no-build").arg("--frozen"), @r###"
-    success: false
-    exit_code: 2
+    uv_snapshot!(context.filters(), context.sync().arg("--no-build").arg("--frozen"), @r"
+    success: true
+    exit_code: 0
     ----- stdout -----
 
     ----- stderr -----
-    error: Distribution `dummy==0.1.0 @ virtual+.` can't be installed because it is marked as `--no-build` but has no binary distribution
-    "###);
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + iniconfig==2.0.0
+    ");
 
     Ok(())
 }

crates/uv/tests/it/sync.rs

@@ -3544,6 +3544,133 @@ fn no_install_project_no_build() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn virtual_no_build() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["anyio==3.7.0"]
+        "#,
+    )?;
+
+    // Generate a lockfile.
+    context.lock().assert().success();
+
+    // Clear the cache.
+    fs_err::remove_dir_all(&context.cache_dir)?;
+
+    // `--no-build` should not raise an error, since we don't install virtual projects.
+    uv_snapshot!(context.filters(), context.sync().arg("--no-build"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    Prepared 3 packages in [TIME]
+    Installed 3 packages in [TIME]
+     + anyio==3.7.0
+     + idna==3.6
+     + sniffio==1.3.1
+    ");
+
+    Ok(())
+}
+
+#[test]
+fn virtual_no_build_dynamic_cached() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dynamic = ["dependencies"]
+
+        [tool.setuptools.dynamic]
+        dependencies = {file = ["requirements.txt"]}
+        "#,
+    )?;
+
+    context
+        .temp_dir
+        .child("requirements.txt")
+        .write_str("anyio==3.7.0")?;
+
+    // Generate a lockfile.
+    context.lock().assert().success();
+
+    // `--no-build` should not raise an error, since we don't build or install the project (given
+    // that it's virtual and the metadata is cached).
+    uv_snapshot!(context.filters(), context.sync().arg("--no-build"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    Prepared 3 packages in [TIME]
+    Installed 3 packages in [TIME]
+     + anyio==3.7.0
+     + idna==3.6
+     + sniffio==1.3.1
+    ");
+
+    Ok(())
+}
+
+#[test]
+fn virtual_no_build_dynamic_no_cache() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dynamic = ["dependencies"]
+
+        [tool.setuptools.dynamic]
+        dependencies = {file = ["requirements.txt"]}
+        "#,
+    )?;
+
+    context
+        .temp_dir
+        .child("requirements.txt")
+        .write_str("anyio==3.7.0")?;
+
+    // Generate a lockfile.
+    context.lock().assert().success();
+
+    // Clear the cache.
+    fs_err::remove_dir_all(&context.cache_dir)?;
+
+    // `--no-build` should raise an error, since we need to build the project.
+    uv_snapshot!(context.filters(), context.sync().arg("--no-build"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Failed to generate package metadata for `project==0.1.0 @ virtual+.`
+      Caused by: Building source distributions for `project` is disabled
+    ");
+
+    Ok(())
+}
+
 /// Convert from a package to a virtual project.
 #[test]
 fn convert_to_virtual() -> Result<()> {
@@ -4815,25 +4942,25 @@ fn no_build_error() -> Result<()> {
     error: Distribution `django-allauth==0.51.0 @ registry+https://pypi.org/simple` can't be installed because it is marked as `--no-build` but has no binary distribution
     "###);
 
-    uv_snapshot!(context.filters(), context.sync().arg("--no-build"), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--no-build"), @r"
     success: false
     exit_code: 2
     ----- stdout -----
 
     ----- stderr -----
     Resolved 19 packages in [TIME]
-    error: Distribution `project==0.1.0 @ virtual+.` can't be installed because it is marked as `--no-build` but has no binary distribution
-    "###);
+    error: Distribution `django-allauth==0.51.0 @ registry+https://pypi.org/simple` can't be installed because it is marked as `--no-build` but has no binary distribution
+    ");
 
-    uv_snapshot!(context.filters(), context.sync().arg("--reinstall").env("UV_NO_BUILD", "1"), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--reinstall").env("UV_NO_BUILD", "1"), @r"
     success: false
     exit_code: 2
     ----- stdout -----
 
     ----- stderr -----
     Resolved 19 packages in [TIME]
-    error: Distribution `project==0.1.0 @ virtual+.` can't be installed because it is marked as `--no-build` but has no binary distribution
-    "###);
+    error: Distribution `django-allauth==0.51.0 @ registry+https://pypi.org/simple` can't be installed because it is marked as `--no-build` but has no binary distribution
+    ");
 
     uv_snapshot!(context.filters(), context.sync().arg("--reinstall").env("UV_NO_BUILD_PACKAGE", "django-allauth"), @r###"
     success: false