uv: add --unstable-uv-lock-file flag to uv pip compile

This flag is hidden, and it is not meant to live forever. Its only
purpose is to provide a way to generate a `uv.lock` using our existing
CLI tooling.

We specifically avoid adding this to persistent configuration to
minimize where it can be used.

crates/uv/Cargo.toml

@@ -58,6 +58,7 @@ tempfile = { workspace = true }
 textwrap = { workspace = true }
 thiserror = { workspace = true }
 tokio = { workspace = true }
+toml = { workspace = true }
 tracing = { workspace = true }
 tracing-durations-export = { workspace = true, features = ["plot"], optional = true }
 tracing-subscriber = { workspace = true, features = ["json"] }

crates/uv/src/cli.rs

@@ -601,6 +601,12 @@ pub(crate) struct PipCompileArgs {
     #[arg(long, overrides_with("emit_index_annotation"), hide = true)]
     pub(crate) no_emit_index_annotation: bool,
 
+    #[arg(long, overrides_with("no_unstable_uv_lock_file"), hide = true)]
+    pub(crate) unstable_uv_lock_file: bool,
+
+    #[arg(long, overrides_with("unstable_uv_lock_file"), hide = true)]
+    pub(crate) no_unstable_uv_lock_file: bool,
+
     #[command(flatten)]
     pub(crate) compat_args: compat::PipCompileCompatArgs,
 }

crates/uv/src/commands/pip_compile.rs

@@ -8,6 +8,7 @@ use std::str::FromStr;
 
 use anstream::{eprint, AutoStream, StripStream};
 use anyhow::{anyhow, Context, Result};
+use fs_err as fs;
 use itertools::Itertools;
 use owo_colors::OwoColorize;
 use tempfile::tempdir_in;
@@ -84,6 +85,7 @@ pub(crate) async fn pip_compile(
     link_mode: LinkMode,
     python: Option<String>,
     system: bool,
+    uv_lock: bool,
     native_tls: bool,
     quiet: bool,
     cache: Cache,
@@ -525,6 +527,12 @@ pub(crate) async fn pip_compile(
         writeln!(writer, "{}", format!("#    {relevant_markers}").green())?;
     }
 
+    if uv_lock {
+        let lock = resolution.lock()?;
+        let encoded = toml::to_string_pretty(&lock)?;
+        fs::tokio::write("uv.lock", encoded.as_bytes()).await?;
+    }
+
     // Write the index locations to the output channel.
     let mut wrote_index = false;
 

crates/uv/src/main.rs

@@ -229,6 +229,7 @@ async fn run() -> Result<ExitStatus> {
                 args.shared.link_mode,
                 args.shared.python,
                 args.shared.system,
+                args.uv_lock,
                 globals.native_tls,
                 globals.quiet,
                 cache,

crates/uv/src/settings.rs

@@ -127,6 +127,7 @@ pub(crate) struct PipCompileSettings {
     pub(crate) r#override: Vec<PathBuf>,
     pub(crate) refresh: Refresh,
     pub(crate) upgrade: Upgrade,
+    pub(crate) uv_lock: bool,
 
     // Shared settings.
     pub(crate) shared: PipSharedSettings,
@@ -194,6 +195,8 @@ impl PipCompileSettings {
             no_emit_marker_expression,
             emit_index_annotation,
             no_emit_index_annotation,
+            unstable_uv_lock_file,
+            no_unstable_uv_lock_file,
             compat_args: _,
         } = args;
 
@@ -207,6 +210,7 @@ impl PipCompileSettings {
             r#override,
             refresh: Refresh::from_args(refresh, refresh_package),
             upgrade: Upgrade::from_args(upgrade, upgrade_package),
+            uv_lock: flag(unstable_uv_lock_file, no_unstable_uv_lock_file).unwrap_or(false),
 
             // Shared settings.
             shared: PipSharedSettings::combine(