Add --force flag for uv cache prune (#16137)

Matching #15992 

See https://github.com/astral-sh/setup-uv/issues/588

crates/uv-cli/src/lib.rs

@@ -802,6 +802,13 @@ pub struct PruneArgs {
     /// that were built from source.
     #[arg(long)]
     pub ci: bool,
+
+    /// Force removal of the cache, ignoring in-use checks.
+    ///
+    /// By default, `uv cache prune` will block until no process is reading the cache. When
+    /// `--force` is used, `uv cache prune` will proceed without taking a lock.
+    #[arg(long)]
+    pub force: bool,
 }
 
 #[derive(Args)]

crates/uv/src/commands/cache_prune.rs

@@ -2,6 +2,7 @@ use std::fmt::Write;
 
 use anyhow::{Context, Result};
 use owo_colors::OwoColorize;
+use tracing::debug;
 
 use uv_cache::{Cache, Removal};
 use uv_fs::Simplified;
@@ -10,7 +11,12 @@ use crate::commands::{ExitStatus, human_readable_bytes};
 use crate::printer::Printer;
 
 /// Prune all unreachable objects from the cache.
-pub(crate) fn cache_prune(ci: bool, cache: Cache, printer: Printer) -> Result<ExitStatus> {
+pub(crate) fn cache_prune(
+    ci: bool,
+    force: bool,
+    cache: Cache,
+    printer: Printer,
+) -> Result<ExitStatus> {
     if !cache.root().exists() {
         writeln!(
             printer.stderr(),
@@ -19,7 +25,19 @@ pub(crate) fn cache_prune(ci: bool, cache: Cache, printer: Printer) -> Result<Ex
         )?;
         return Ok(ExitStatus::Success);
     }
-    let cache = cache.with_exclusive_lock()?;
+
+    let cache = if force {
+        // If `--force` is used, attempt to acquire the exclusive lock but do not block.
+        match cache.with_exclusive_lock_no_wait() {
+            Ok(cache) => cache,
+            Err(cache) => {
+                debug!("Cache is currently in use, proceeding due to `--force`");
+                cache
+            }
+        }
+    } else {
+        cache.with_exclusive_lock()?
+    };
 
     writeln!(
         printer.stderr(),

crates/uv/src/lib.rs

@@ -1023,7 +1023,7 @@ async fn run(mut cli: Cli) -> Result<ExitStatus> {
             command: CacheCommand::Prune(args),
         }) => {
             show_settings!(args);
-            commands::cache_prune(args.ci, cache, printer)
+            commands::cache_prune(args.ci, args.force, cache, printer)
         }
         Commands::Cache(CacheNamespace {
             command: CacheCommand::Dir,

crates/uv/tests/it/cache_prune.rs

@@ -196,6 +196,57 @@ fn prune_stale_symlink() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn prune_force() -> Result<()> {
+    let context = TestContext::new("3.12").with_filtered_counts();
+
+    let requirements_txt = context.temp_dir.child("requirements.txt");
+    requirements_txt.write_str("typing-extensions\niniconfig")?;
+
+    // Install a requirement, to populate the cache.
+    context
+        .pip_sync()
+        .arg("requirements.txt")
+        .assert()
+        .success();
+
+    // When unlocked, `--force` should still take a lock
+    uv_snapshot!(context.filters(), context.prune().arg("--verbose").arg("--force"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    DEBUG uv [VERSION] ([COMMIT] DATE)
+    DEBUG Acquired lock for `[CACHE_DIR]/`
+    Pruning cache at: [CACHE_DIR]/
+    No unused entries found
+    DEBUG Released lock at `[CACHE_DIR]/.lock`
+    ");
+
+    // Add a stale directory to the cache.
+    let simple = context.cache_dir.child("simple-v4");
+    simple.create_dir_all()?;
+
+    // When locked, `--force` should proceed without blocking
+    let _cache = uv_cache::Cache::from_path(context.cache_dir.path()).with_exclusive_lock();
+    uv_snapshot!(context.filters(), context.prune().arg("--verbose").arg("--force"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    DEBUG uv [VERSION] ([COMMIT] DATE)
+    DEBUG Lock is busy for `[CACHE_DIR]/`
+    DEBUG Cache is currently in use, proceeding due to `--force`
+    Pruning cache at: [CACHE_DIR]/
+    DEBUG Removing dangling cache bucket: [CACHE_DIR]/simple-v4
+    Removed 1 directory
+    ");
+
+    Ok(())
+}
+
 /// `cache prune --ci` should remove all unzipped archives.
 #[test]
 fn prune_unzipped() -> Result<()> {