Fix handling of UV_NO_SYNC=1 uv run ... (#17391)

Closes #17390

---------

Co-authored-by: Claude <noreply@anthropic.com>

crates/uv/src/settings.rs

@@ -620,6 +620,7 @@ impl RunSettings {
         // Resolve flags from CLI and environment variables.
         let locked = resolve_flag(locked, "locked", environment.locked);
         let frozen = resolve_flag(frozen, "frozen", environment.frozen);
+        let no_sync = resolve_flag(no_sync, "no-sync", environment.no_sync);
 
         // Check for conflicts between locked and frozen.
         check_conflicts(locked, frozen);
@@ -677,7 +678,7 @@ impl RunSettings {
             all_packages,
             package,
             no_project,
-            no_sync,
+            no_sync: no_sync.is_enabled(),
             active: flag(active, no_active, "active"),
             python: python.and_then(Maybe::into_option),
             python_platform,

crates/uv/tests/it/run.rs

@@ -2433,6 +2433,65 @@ fn run_no_sync() -> Result<()> {
     Ok(())
 }
 
+/// Test that `UV_NO_SYNC=1` environment variable works for `uv run`.
+///
+/// See: <https://github.com/astral-sh/uv/issues/17390>
+#[test]
+fn run_no_sync_env_var() -> 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"]
+
+        [build-system]
+        requires = ["setuptools>=42"]
+        build-backend = "setuptools.build_meta"
+        "#,
+    )?;
+
+    // Running with `UV_NO_SYNC=1` should succeed, even if the lockfile isn't present.
+    uv_snapshot!(context.filters(), context.run().env(EnvVars::UV_NO_SYNC, "1").arg("--").arg("python").arg("--version"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Python 3.12.[X]
+
+    ----- stderr -----
+    "###);
+
+    context.lock().assert().success();
+
+    // Running with `UV_NO_SYNC=1` should not install any requirements.
+    uv_snapshot!(context.filters(), context.run().env(EnvVars::UV_NO_SYNC, "1").arg("--").arg("python").arg("--version"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Python 3.12.[X]
+
+    ----- stderr -----
+    "###);
+
+    context.sync().assert().success();
+
+    // But it should have access to the installed packages.
+    uv_snapshot!(context.filters(), context.run().env(EnvVars::UV_NO_SYNC, "1").arg("--").arg("python").arg("-c").arg("import anyio; print(anyio.__name__)"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    anyio
+
+    ----- stderr -----
+    "###);
+
+    Ok(())
+}
+
 #[test]
 fn run_empty_requirements_txt() -> Result<()> {
     let context = TestContext::new("3.12");