Set UV to the uv executable path (#11326)

crates/uv-static/src/env_vars.rs

@@ -5,6 +5,17 @@ pub struct EnvVars;
 
 #[attribute_env_vars_metadata]
 impl EnvVars {
+    /// The path to the binary that was used to invoke uv.
+    ///
+    /// This is propagated to all subprocesses spawned by uv.
+    ///
+    /// If the executable was invoked through a symbolic link, some platforms will return the path
+    /// of the symbolic link and other platforms will return the path of the symbolic link’s target.
+    ///
+    /// See <https://doc.rust-lang.org/std/env/fn.current_exe.html#security> for security
+    /// considerations.
+    pub const UV: &'static str = "UV";
+
     /// Equivalent to the `--offline` command-line argument. If set, uv will disable network access.
     pub const UV_OFFLINE: &'static str = "UV_OFFLINE";
 

crates/uv/src/bin/uv.rs

@@ -7,6 +7,8 @@ use std::process::ExitCode;
 
 use uv::main as uv_main;
 
+#[allow(unsafe_code)]
 fn main() -> ExitCode {
-    uv_main(std::env::args_os())
+    // SAFETY: This is safe because we are running it early in `main` before spawning any threads.
+    unsafe { uv_main(std::env::args_os()) }
 }

crates/uv/src/lib.rs

@@ -1813,16 +1813,35 @@ async fn run_project(
 
 /// The main entry point for a uv invocation.
 ///
-/// WARNING: This entry point is not recommended for external consumption, the
-/// uv binary interface is the official public API. When using this entry
-/// point, uv assumes it is running in a process it controls and that the
-/// entire process lifetime is managed by uv. Unexpected behavior may be
-/// encountered if this entry point is called multiple times in a single process.
-pub fn main<I, T>(args: I) -> ExitCode
+/// # Usage
+///
+/// This entry point is not recommended for external consumption, the uv binary interface is the
+/// official public API.
+///
+/// When using this entry point, uv assumes it is running in a process it controls and that the
+/// entire process lifetime is managed by uv. Unexpected behavior may be encountered if this entry
+/// point is called multiple times in a single process.
+///
+/// # Safety
+///
+/// It is only safe to call this routine when it is known that multiple threads are not running.
+#[allow(unsafe_code)]
+pub unsafe fn main<I, T>(args: I) -> ExitCode
 where
     I: IntoIterator<Item = T>,
     T: Into<OsString> + Clone,
 {
+    // Set the `UV` variable to the current executable so it is implicitly propagated to all child
+    // processes, e.g., in `uv run`.
+    if let Ok(current_exe) = std::env::current_exe() {
+        // SAFETY: The proof obligation must be satisfied by the caller.
+        unsafe {
+            // This will become unsafe in Rust 2024
+            // See https://doc.rust-lang.org/std/env/fn.set_var.html#safety
+            std::env::set_var(EnvVars::UV, current_exe);
+        }
+    }
+
     // `std::env::args` is not `Send` so we parse before passing to our runtime
     // https://github.com/rust-lang/rust/pull/48005
     let cli = match Cli::try_parse_from(args) {

crates/uv/tests/it/common/mod.rs

@@ -362,6 +362,12 @@ impl TestContext {
 
         let mut filters = Vec::new();
 
+        filters.extend(
+            Self::path_patterns(get_bin())
+                .into_iter()
+                .map(|pattern| (pattern, "[UV]".to_string())),
+        );
+
         // Exclude `link-mode` on Windows since we set it in the remote test suite
         if cfg!(windows) {
             filters.push((" --link-mode <LINK_MODE>".to_string(), String::new()));

crates/uv/tests/it/run.rs

@@ -4350,3 +4350,20 @@ fn detect_infinite_recursion() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn run_uv_variable() {
+    let context = TestContext::new("3.12");
+
+    // Display the `UV` variable
+    uv_snapshot!(
+        context.filters(),
+        context.run().arg("python").arg("-c").arg("import os; print(os.environ['UV'])"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [UV]
+
+    ----- stderr -----
+    "###);
+}