Rewrite Python interpreter discovery

# Conflicts:
#	crates/uv-interpreter/src/environment/python_environment.rs
#	crates/uv-interpreter/src/find_python.rs
#	crates/uv-interpreter/src/interpreter.rs
#	crates/uv-virtualenv/src/bare.rs

# Conflicts:
#	crates/uv-virtualenv/src/bare.rs

# Conflicts:
#	crates/uv-interpreter/src/find_python.rs
#	crates/uv-interpreter/src/implementation.rs
#	crates/uv-interpreter/src/interpreter.rs
#	crates/uv-interpreter/src/lib.rs
#	crates/uv-interpreter/src/managed/find.rs
#	crates/uv-interpreter/src/py_launcher.rs

# Conflicts:
#	crates/uv-interpreter/src/find_python.rs

# Conflicts:
#	crates/uv/src/commands/run.rs

# Conflicts:
#	crates/uv-interpreter/src/environment.rs
#	crates/uv-interpreter/src/find_python.rs
#	crates/uv-interpreter/src/lib.rs
#	crates/uv-interpreter/src/py_launcher.rs
#	crates/uv-resolver/tests/resolver.rs
#	crates/uv/src/commands/project/run.rs
#	crates/uv/tests/pip_sync.rs

# Conflicts:
#	crates/uv-interpreter/src/find_python.rs
#	crates/uv/src/commands/pip/install.rs
#	crates/uv/src/commands/pip/sync.rs

# Conflicts:
#	crates/uv-interpreter/src/interpreter.rs
#	crates/uv-interpreter/src/lib.rs

# Conflicts:
#	crates/uv-interpreter/src/find_python.rs
#	crates/uv-interpreter/src/py_launcher.rs
#	crates/uv-resolver/tests/resolver.rs
#	crates/uv-virtualenv/src/main.rs

# Conflicts:
#	crates/uv-interpreter/Cargo.toml
#	crates/uv-interpreter/src/environment.rs
#	crates/uv/src/commands/project/mod.rs
#	crates/uv/src/commands/project/run.rs

.github/workflows/ci.yml

@@ -144,6 +144,7 @@ jobs:
 
       - name: "Cargo test"
         run: |
+          export UV_BOOTSTRAP_DIR="$(pwd)/bin"
           cargo nextest run \
             --workspace \
             --status-level skip --failure-output immediate-final --no-fail-fast -j 12 --final-status-level slow

crates/uv-dev/src/fetch_python.rs

@@ -25,11 +25,13 @@ pub(crate) struct FetchPythonArgs {
 pub(crate) async fn fetch_python(args: FetchPythonArgs) -> Result<()> {
     let start = Instant::now();
 
-    let bootstrap_dir = TOOLCHAIN_DIRECTORY
-        .as_ref()
-        .expect("The toolchain directory must exist for bootstrapping");
+    let bootstrap_dir = TOOLCHAIN_DIRECTORY.clone().unwrap_or_else(|| {
+        std::env::current_dir()
+            .expect("Use `UV_BOOTSTRAP_DIR` if the current directory is not usable.")
+            .join("bin")
+    });
 
-    fs_err::create_dir_all(bootstrap_dir)?;
+    fs_err::create_dir_all(&bootstrap_dir)?;
 
     let versions = if args.versions.is_empty() {
         info!("Reading versions from file...");
@@ -59,7 +61,7 @@ pub(crate) async fn fetch_python(args: FetchPythonArgs) -> Result<()> {
     let mut tasks = futures::stream::iter(downloads.iter())
         .map(|download| {
             async {
-                let result = download.fetch(&client, bootstrap_dir).await;
+                let result = download.fetch(&client, &bootstrap_dir).await;
                 (download.python_version(), result)
             }
             .instrument(info_span!("download", key = %download))
@@ -130,6 +132,10 @@ pub(crate) async fn fetch_python(args: FetchPythonArgs) -> Result<()> {
     };
 
     info!("Installed {} versions", requests.len());
+    info!(
+        r#"To enable discovery: export UV_BOOTSTRAP_DIR="{}""#,
+        bootstrap_dir.display()
+    );
 
     Ok(())
 }

crates/uv-interpreter/Cargo.toml

@@ -51,7 +51,9 @@ winapi = { workspace = true }
 
 [dev-dependencies]
 anyhow = { version = "1.0.80" }
+assert_fs = { version = "1.1.1" }
 indoc = { version = "2.0.4" }
-insta = { version = "1.36.1", features = ["filters"] }
 itertools = { version = "0.13.0" }
+temp-env = { version = "0.3.6" }
 tempfile = { version = "3.9.0" }
+test-log = { version = "0.2.15", features = ["trace"], default-features = false }