Make uv.sources without --preview non-fatal (#4558)

## Summary

Like other preview usages, this should just warn.

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

@@ -40,8 +40,6 @@ pub enum LoweringError {
     ForbiddenFragment(Url),
     #[error("`workspace = false` is not yet supported")]
     WorkspaceFalse,
-    #[error("`tool.uv.sources` is a preview feature; use `--preview` or set `UV_PREVIEW=1` to enable it")]
-    MissingPreview,
     #[error("Editable must refer to a local directory, not a file: `{0}`")]
     EditableFile(String),
     #[error(transparent)] // Function attaches the context
@@ -95,7 +93,7 @@ pub(crate) fn lower_requirement(
     };
 
     if preview.is_disabled() {
-        return Err(LoweringError::MissingPreview);
+        warn_user_once!("`uv.sources` is experimental and may change without warning.");
     }
 
     let source = match source {

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

@@ -1,19 +1,19 @@
 use anyhow::{Context, Result};
+
+use uv_cache::Cache;
 use uv_client::{BaseClientBuilder, Connectivity, FlatIndexClient, RegistryClientBuilder};
+use uv_configuration::{Concurrency, ExtrasSpecification, PreviewMode, SetupPyStrategy};
 use uv_dispatch::BuildDispatch;
 use uv_distribution::pyproject::{Source, SourceError};
 use uv_distribution::pyproject_mut::PyProjectTomlMut;
+use uv_distribution::{DistributionDatabase, ProjectWorkspace, Workspace};
 use uv_git::GitResolver;
+use uv_normalize::PackageName;
 use uv_requirements::{NamedRequirementsResolver, RequirementsSource, RequirementsSpecification};
 use uv_resolver::{FlatIndex, InMemoryIndex};
 use uv_toolchain::{ToolchainPreference, ToolchainRequest};
 use uv_types::{BuildIsolation, HashStrategy, InFlight};
-
-use uv_cache::Cache;
-use uv_configuration::{Concurrency, ExtrasSpecification, PreviewMode, SetupPyStrategy};
-use uv_distribution::{DistributionDatabase, ProjectWorkspace, Workspace};
-use uv_normalize::PackageName;
-use uv_warnings::warn_user;
+use uv_warnings::warn_user_once;
 
 use crate::commands::pip::operations::Modifications;
 use crate::commands::pip::resolution_environment;
@@ -44,7 +44,7 @@ pub(crate) async fn add(
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv add` is experimental and may change without warning.");
+        warn_user_once!("`uv add` is experimental and may change without warning.");
     }
 
     // Find the project in the workspace.

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

@@ -15,7 +15,7 @@ use uv_resolver::{
 };
 use uv_toolchain::{Interpreter, ToolchainPreference, ToolchainRequest};
 use uv_types::{BuildIsolation, EmptyInstalledPackages, HashStrategy, InFlight};
-use uv_warnings::warn_user;
+use uv_warnings::{warn_user, warn_user_once};
 
 use crate::commands::project::{find_requires_python, ProjectError};
 use crate::commands::{pip, project, ExitStatus};
@@ -36,7 +36,7 @@ pub(crate) async fn lock(
     printer: Printer,
 ) -> anyhow::Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv lock` is experimental and may change without warning.");
+        warn_user_once!("`uv lock` is experimental and may change without warning.");
     }
 
     // Find the project requirements.

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

@@ -7,7 +7,7 @@ use uv_configuration::{Concurrency, ExtrasSpecification, PreviewMode};
 use uv_distribution::pyproject_mut::PyProjectTomlMut;
 use uv_distribution::{ProjectWorkspace, Workspace};
 use uv_toolchain::{ToolchainPreference, ToolchainRequest};
-use uv_warnings::warn_user;
+use uv_warnings::{warn_user, warn_user_once};
 
 use crate::commands::pip::operations::Modifications;
 use crate::commands::{project, ExitStatus};
@@ -30,7 +30,7 @@ pub(crate) async fn remove(
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv remove` is experimental and may change without warning.");
+        warn_user_once!("`uv remove` is experimental and may change without warning.");
     }
 
     // Find the project in the workspace.

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

@@ -18,7 +18,7 @@ use uv_toolchain::{
     EnvironmentPreference, Interpreter, PythonEnvironment, Toolchain, ToolchainPreference,
     ToolchainRequest,
 };
-use uv_warnings::warn_user;
+use uv_warnings::warn_user_once;
 
 use crate::commands::pip::operations::Modifications;
 use crate::commands::{project, ExitStatus};
@@ -45,7 +45,7 @@ pub(crate) async fn run(
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv run` is experimental and may change without warning.");
+        warn_user_once!("`uv run` is experimental and may change without warning.");
     }
 
     // Discover and sync the base environment.

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

@@ -13,7 +13,7 @@ use uv_normalize::PackageName;
 use uv_resolver::{FlatIndex, InMemoryIndex, Lock};
 use uv_toolchain::{PythonEnvironment, ToolchainPreference, ToolchainRequest};
 use uv_types::{BuildIsolation, HashStrategy, InFlight};
-use uv_warnings::warn_user;
+use uv_warnings::warn_user_once;
 
 use crate::commands::pip::operations::Modifications;
 use crate::commands::project::ProjectError;
@@ -38,7 +38,7 @@ pub(crate) async fn sync(
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv sync` is experimental and may change without warning.");
+        warn_user_once!("`uv sync` is experimental and may change without warning.");
     }
 
     // Find the project requirements.

crates/uv/src/commands/tool/install.rs

@@ -15,7 +15,7 @@ use uv_installer::SitePackages;
 use uv_requirements::RequirementsSource;
 use uv_tool::{entrypoint_paths, find_executable_directory, InstalledTools, Tool};
 use uv_toolchain::{EnvironmentPreference, Toolchain, ToolchainPreference, ToolchainRequest};
-use uv_warnings::warn_user;
+use uv_warnings::warn_user_once;
 
 use crate::commands::project::update_environment;
 use crate::commands::ExitStatus;
@@ -39,7 +39,7 @@ pub(crate) async fn install(
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv tool install` is experimental and may change without warning.");
+        warn_user_once!("`uv tool install` is experimental and may change without warning.");
     }
 
     let installed_tools = InstalledTools::from_settings()?;

crates/uv/src/commands/tool/run.rs

@@ -13,7 +13,7 @@ use uv_requirements::RequirementsSource;
 use uv_toolchain::{
     EnvironmentPreference, PythonEnvironment, Toolchain, ToolchainPreference, ToolchainRequest,
 };
-use uv_warnings::warn_user;
+use uv_warnings::warn_user_once;
 
 use crate::commands::project::update_environment;
 use crate::commands::ExitStatus;
@@ -38,7 +38,7 @@ pub(crate) async fn run(
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv tool run` is experimental and may change without warning.");
+        warn_user_once!("`uv tool run` is experimental and may change without warning.");
     }
 
     let (target, args) = command.split();

crates/uv/src/commands/toolchain/find.rs

@@ -5,7 +5,7 @@ use uv_cache::Cache;
 use uv_configuration::PreviewMode;
 use uv_fs::Simplified;
 use uv_toolchain::{EnvironmentPreference, Toolchain, ToolchainPreference, ToolchainRequest};
-use uv_warnings::warn_user;
+use uv_warnings::warn_user_once;
 
 use crate::commands::ExitStatus;
 use crate::printer::Printer;
@@ -19,7 +19,7 @@ pub(crate) async fn find(
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv toolchain find` is experimental and may change without warning.");
+        warn_user_once!("`uv toolchain find` is experimental and may change without warning.");
     }
 
     let request = match request {

crates/uv/src/commands/toolchain/install.rs

@@ -9,7 +9,7 @@ use uv_fs::Simplified;
 use uv_toolchain::downloads::{self, DownloadResult, PythonDownload, PythonDownloadRequest};
 use uv_toolchain::managed::{InstalledToolchain, InstalledToolchains};
 use uv_toolchain::{requests_from_version_file, ToolchainRequest};
-use uv_warnings::warn_user;
+use uv_warnings::warn_user_once;
 
 use crate::commands::ExitStatus;
 use crate::printer::Printer;
@@ -25,7 +25,7 @@ pub(crate) async fn install(
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv toolchain install` is experimental and may change without warning.");
+        warn_user_once!("`uv toolchain install` is experimental and may change without warning.");
     }
 
     let start = std::time::Instant::now();

crates/uv/src/commands/toolchain/list.rs

@@ -11,7 +11,7 @@ use uv_toolchain::{
     find_toolchains, DiscoveryError, EnvironmentPreference, Toolchain, ToolchainNotFound,
     ToolchainPreference, ToolchainRequest, ToolchainSource,
 };
-use uv_warnings::warn_user;
+use uv_warnings::warn_user_once;
 
 use crate::commands::ExitStatus;
 use crate::printer::Printer;
@@ -35,7 +35,7 @@ pub(crate) async fn list(
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
-        warn_user!("`uv toolchain list` is experimental and may change without warning.");
+        warn_user_once!("`uv toolchain list` is experimental and may change without warning.");
     }
 
     let download_request = match kinds {

crates/uv/tests/pip_install.rs

@@ -5485,26 +5485,27 @@ fn tool_uv_sources_is_in_preview() -> Result<()> {
         name = "foo"
         version = "0.0.0"
         dependencies = [
-          "tqdm>4,<=5",
+          "iniconfig>1,<=2",
         ]
 
         [tool.uv.sources]
-        tqdm = { url = "https://files.pythonhosted.org/packages/a5/d6/502a859bac4ad5e274255576cd3e15ca273cdb91731bc39fb840dd422ee9/tqdm-4.66.0-py3-none-any.whl" }
+        iniconfig = { url = "https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl" }
     "#})?;
 
     // Install the editable packages.
-    uv_snapshot!(context.filters(), windows_filters=false, context.pip_install()
+    uv_snapshot!(context.filters(), context.pip_install()
         .arg("-r")
-        .arg("pyproject.toml")
-        .arg("--extra")
-        .arg("utils"), @r###"
-    success: false
-    exit_code: 2
+        .arg("pyproject.toml"), @r###"
+    success: true
+    exit_code: 0
     ----- stdout -----
 
     ----- stderr -----
-    error: Failed to parse entry for: `tqdm`
-      Caused by: `tool.uv.sources` is a preview feature; use `--preview` or set `UV_PREVIEW=1` to enable it
+    warning: `uv.sources` is experimental and may change without warning.
+    Resolved 1 package in [TIME]
+    Prepared 1 package in [TIME]
+    Installed 1 package in [TIME]
+     + iniconfig==2.0.0 (from https://files.pythonhosted.org/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl)
     "###
     );