feat(venv): add relocatable flag (#5515)

## Summary

Adds a `--relocatable` CLI arg to `uv venv`. This flag does two things:

* ensures that the associated activation scripts do not rely on a
hardcoded
absolute path to the virtual environment (to the extent possible; `.csh`
and
  `.nu` left as-is)
* persists a `relocatable` flag in `pyvenv.cfg`.

The flag in `pyvenv.cfg` in turn instructs the wheel `Installer` to
create script
entrypoints in a relocatable way (use `exec` trick + `dirname $0` on
POSIX;
use relative path to `python[w].exe` on Windows).

Fixes: #3863

## Test Plan

* Relocatable console scripts covered as additional scenarios in
existing test cases.
* Integration testing of boilerplate generation in `venv`.
* Manual testing of `uv venv` with and without `--relocatable`

crates/install-wheel-rs/src/lib.rs

@@ -1,7 +1,6 @@
 //! Takes a wheel and installs it into a venv.
 
 use std::io;
-
 use std::path::PathBuf;
 
 use platform_info::PlatformInfoError;

crates/install-wheel-rs/src/linker.rs

@@ -37,6 +37,7 @@ pub struct Locks(Mutex<FxHashMap<PathBuf, Arc<Mutex<()>>>>);
 #[instrument(skip_all, fields(wheel = %filename))]
 pub fn install_wheel(
     layout: &Layout,
+    relocatable: bool,
     wheel: impl AsRef<Path>,
     filename: &WheelFilename,
     direct_url: Option<&DirectUrl>,
@@ -97,8 +98,22 @@ pub fn install_wheel(
         debug!(?name, "Writing entrypoints");
 
         fs_err::create_dir_all(&layout.scheme.scripts)?;
-        write_script_entrypoints(layout, site_packages, &console_scripts, &mut record, false)?;
-        write_script_entrypoints(layout, site_packages, &gui_scripts, &mut record, true)?;
+        write_script_entrypoints(
+            layout,
+            relocatable,
+            site_packages,
+            &console_scripts,
+            &mut record,
+            false,
+        )?;
+        write_script_entrypoints(
+            layout,
+            relocatable,
+            site_packages,
+            &gui_scripts,
+            &mut record,
+            true,
+        )?;
     }
 
     // 2.a Unpacked archive includes distribution-1.0.dist-info/ and (if there is data) distribution-1.0.data/.
@@ -108,6 +123,7 @@ pub fn install_wheel(
         debug!(?name, "Installing data");
         install_data(
             layout,
+            relocatable,
             site_packages,
             &data_dir,
             &name,

crates/install-wheel-rs/src/wheel.rs

@@ -1,5 +1,5 @@
 use std::collections::HashMap;
-use std::io::{BufRead, BufReader, Cursor, Read, Write};
+use std::io::{BufRead, BufReader, Cursor, Read, Seek, Write};
 use std::path::{Path, PathBuf};
 use std::{env, io};
 
@@ -128,7 +128,7 @@ fn copy_and_hash(reader: &mut impl Read, writer: &mut impl Write) -> io::Result<
 /// executable.
 ///
 /// See: <https://github.com/pypa/pip/blob/0ad4c94be74cc24874c6feb5bb3c2152c398a18e/src/pip/_vendor/distlib/scripts.py#L136-L165>
-fn format_shebang(executable: impl AsRef<Path>, os_name: &str) -> String {
+fn format_shebang(executable: impl AsRef<Path>, os_name: &str, relocatable: bool) -> String {
     // Convert the executable to a simplified path.
     let executable = executable.as_ref().simplified_display().to_string();
 
@@ -139,11 +139,18 @@ fn format_shebang(executable: impl AsRef<Path>, os_name: &str) -> String {
         let shebang_length = 2 + executable.len() + 1;
 
         // If the shebang is too long, or contains spaces, wrap it in `/bin/sh`.
-        if shebang_length > 127 || executable.contains(' ') {
+        // Same applies for relocatable scripts (executable is relative to script dir, hence `dirname` trick)
+        // (note: the Windows trampoline binaries natively support relative paths to executable)
+        if shebang_length > 127 || executable.contains(' ') || relocatable {
+            let prefix = if relocatable {
+                r#""$(CDPATH= cd -- "$(dirname -- "$0")" && echo "$PWD")"/"#
+            } else {
+                ""
+            };
             // Like Python's `shlex.quote`:
             // > Use single quotes, and put single quotes into double quotes
             // > The string $'b is then quoted as '$'"'"'b'
-            let executable = format!("'{}'", executable.replace('\'', r#"'"'"'"#));
+            let executable = format!("{}'{}'", prefix, executable.replace('\'', r#"'"'"'"#));
             return format!("#!/bin/sh\n'''exec' {executable} \"$0\" \"$@\"\n' '''");
         }
     }
@@ -272,6 +279,7 @@ fn entrypoint_path(entrypoint: &Script, layout: &Layout) -> PathBuf {
 /// Create the wrapper scripts in the bin folder of the venv for launching console scripts.
 pub(crate) fn write_script_entrypoints(
     layout: &Layout,
+    relocatable: bool,
     site_packages: &Path,
     entrypoints: &[Script],
     record: &mut Vec<RecordEntry>,
@@ -293,9 +301,11 @@ pub(crate) fn write_script_entrypoints(
 
         // Generate the launcher script.
         let launcher_executable = get_script_executable(&layout.sys_executable, is_gui);
+        let launcher_executable =
+            get_relocatable_executable(launcher_executable, layout, relocatable)?;
         let launcher_python_script = get_script_launcher(
             entrypoint,
-            &format_shebang(&launcher_executable, &layout.os_name),
+            &format_shebang(&launcher_executable, &layout.os_name, relocatable),
         );
 
         // If necessary, wrap the launcher script in a Windows launcher binary.
@@ -432,11 +442,12 @@ pub(crate) fn move_folder_recorded(
     Ok(())
 }
 
-/// Installs a single script (not an entrypoint)
+/// Installs a single script (not an entrypoint).
 ///
-/// Has to deal with both binaries files (just move) and scripts (rewrite the shebang if applicable)
+/// Has to deal with both binaries files (just move) and scripts (rewrite the shebang if applicable).
 fn install_script(
     layout: &Layout,
+    relocatable: bool,
     site_packages: &Path,
     record: &mut [RecordEntry],
     file: &DirEntry,
@@ -494,7 +505,19 @@ fn install_script(
     let mut start = vec![0; placeholder_python.len()];
     script.read_exact(&mut start)?;
     let size_and_encoded_hash = if start == placeholder_python {
-        let start = format_shebang(&layout.sys_executable, &layout.os_name)
+        let is_gui = {
+            let mut buf = vec![0; 1];
+            script.read_exact(&mut buf)?;
+            if buf == b"w" {
+                true
+            } else {
+                script.seek_relative(-1)?;
+                false
+            }
+        };
+        let executable = get_script_executable(&layout.sys_executable, is_gui);
+        let executable = get_relocatable_executable(executable, layout, relocatable)?;
+        let start = format_shebang(&executable, &layout.os_name, relocatable)
             .as_bytes()
             .to_vec();
 
@@ -555,6 +578,7 @@ fn install_script(
 #[instrument(skip_all)]
 pub(crate) fn install_data(
     layout: &Layout,
+    relocatable: bool,
     site_packages: &Path,
     data_dir: &Path,
     dist_name: &PackageName,
@@ -598,7 +622,7 @@ pub(crate) fn install_data(
                         initialized = true;
                     }
 
-                    install_script(layout, site_packages, record, &file)?;
+                    install_script(layout, relocatable, site_packages, record, &file)?;
                 }
             }
             Some("headers") => {
@@ -682,6 +706,31 @@ pub(crate) fn extra_dist_info(
     Ok(())
 }
 
+/// Get the path to the Python executable for the [`Layout`], based on whether the wheel should
+/// be relocatable.
+///
+/// Returns `sys.executable` if the wheel is not relocatable; otherwise, returns a path relative
+/// to the scripts directory.
+pub(crate) fn get_relocatable_executable(
+    executable: PathBuf,
+    layout: &Layout,
+    relocatable: bool,
+) -> Result<PathBuf, Error> {
+    Ok(if relocatable {
+        pathdiff::diff_paths(&executable, &layout.scheme.scripts).ok_or_else(|| {
+            Error::Io(io::Error::new(
+                io::ErrorKind::Other,
+                format!(
+                    "Could not find relative path for: {}",
+                    executable.simplified_display()
+                ),
+            ))
+        })?
+    } else {
+        executable
+    })
+}
+
 /// Reads the record file
 /// <https://www.python.org/dev/peps/pep-0376/#record>
 pub fn read_record_file(record: &mut impl Read) -> Result<Vec<RecordEntry>, Error> {
@@ -845,33 +894,47 @@ mod test {
         // By default, use a simple shebang.
         let executable = Path::new("/usr/bin/python3");
         let os_name = "posix";
-        assert_eq!(format_shebang(executable, os_name), "#!/usr/bin/python3");
+        assert_eq!(
+            format_shebang(executable, os_name, false),
+            "#!/usr/bin/python3"
+        );
 
         // If the path contains spaces, we should use the `exec` trick.
         let executable = Path::new("/usr/bin/path to python3");
         let os_name = "posix";
         assert_eq!(
-            format_shebang(executable, os_name),
+            format_shebang(executable, os_name, false),
             "#!/bin/sh\n'''exec' '/usr/bin/path to python3' \"$0\" \"$@\"\n' '''"
         );
 
+        // And if we want a relocatable script, we should use the `exec` trick with `dirname`.
+        let executable = Path::new("python3");
+        let os_name = "posix";
+        assert_eq!(
+            format_shebang(executable, os_name, true),
+            "#!/bin/sh\n'''exec' \"$(CDPATH= cd -- \"$(dirname -- \"$0\")\" && echo \"$PWD\")\"/'python3' \"$0\" \"$@\"\n' '''"
+        );
+
         // Except on Windows...
         let executable = Path::new("/usr/bin/path to python3");
         let os_name = "nt";
         assert_eq!(
-            format_shebang(executable, os_name),
+            format_shebang(executable, os_name, false),
             "#!/usr/bin/path to python3"
         );
 
         // Quotes, however, are ok.
         let executable = Path::new("/usr/bin/'python3'");
         let os_name = "posix";
-        assert_eq!(format_shebang(executable, os_name), "#!/usr/bin/'python3'");
+        assert_eq!(
+            format_shebang(executable, os_name, false),
+            "#!/usr/bin/'python3'"
+        );
 
         // If the path is too long, we should not use the `exec` trick.
         let executable = Path::new("/usr/bin/path/to/a/very/long/executable/executable/executable/executable/executable/executable/executable/executable/name/python3");
         let os_name = "posix";
-        assert_eq!(format_shebang(executable, os_name), "#!/bin/sh\n'''exec' '/usr/bin/path/to/a/very/long/executable/executable/executable/executable/executable/executable/executable/executable/name/python3' \"$0\" \"$@\"\n' '''");
+        assert_eq!(format_shebang(executable, os_name, false), "#!/bin/sh\n'''exec' '/usr/bin/path/to/a/very/long/executable/executable/executable/executable/executable/executable/executable/executable/name/python3' \"$0\" \"$@\"\n' '''");
     }
 
     #[test]

crates/uv-build/src/lib.rs

@@ -442,6 +442,7 @@ impl SourceBuild {
                 uv_virtualenv::Prompt::None,
                 false,
                 false,
+                false,
             )?,
             BuildIsolation::Shared(venv) => venv.clone(),
         };

crates/uv-cli/src/lib.rs

@@ -1743,6 +1743,22 @@ pub struct VenvArgs {
     #[arg(long)]
     pub system_site_packages: bool,
 
+    /// Make the virtual environment relocatable.
+    ///
+    /// A relocatable virtual environment can be moved around and redistributed without
+    /// invalidating its associated entrypoint and activation scripts.
+    ///
+    /// Note that this can only be guaranteed for standard `console_scripts` and `gui_scripts`.
+    /// Other scripts may be adjusted if they ship with a generic `#!python[w]` shebang,
+    /// and binaries are left as-is.
+    ///
+    /// As a result of making the environment relocatable (by way of writing relative, rather than
+    /// absolute paths), the entrypoints and scripts themselves will _not_ be relocatable. In other
+    /// words, copying those entrypoints and scripts to a location outside the environment will not
+    /// work, as they reference paths relative to the environment itself.
+    #[arg(long)]
+    pub relocatable: bool,
+
     #[command(flatten)]
     pub index_args: IndexArgs,
 

crates/uv-installer/src/installer.rs

@@ -85,8 +85,16 @@ impl<'a> Installer<'a> {
         let (tx, rx) = oneshot::channel();
 
         let layout = venv.interpreter().layout();
+        let relocatable = venv.relocatable();
         rayon::spawn(move || {
-            let result = install(wheels, layout, installer_name, link_mode, reporter);
+            let result = install(
+                wheels,
+                layout,
+                installer_name,
+                link_mode,
+                reporter,
+                relocatable,
+            );
             tx.send(result).unwrap();
         });
 
@@ -112,6 +120,7 @@ impl<'a> Installer<'a> {
             self.installer_name,
             self.link_mode,
             self.reporter,
+            self.venv.relocatable(),
         )
     }
 }
@@ -124,11 +133,13 @@ fn install(
     installer_name: Option<String>,
     link_mode: LinkMode,
     reporter: Option<Box<dyn Reporter>>,
+    relocatable: bool,
 ) -> Result<Vec<CachedDist>> {
     let locks = install_wheel_rs::linker::Locks::default();
     wheels.par_iter().try_for_each(|wheel| {
         install_wheel_rs::linker::install_wheel(
             &layout,
+            relocatable,
             wheel.path(),
             wheel.filename(),
             wheel

crates/uv-python/src/environment.rs

@@ -162,6 +162,11 @@ impl PythonEnvironment {
         Ok(PyVenvConfiguration::parse(self.0.root.join("pyvenv.cfg"))?)
     }
 
+    /// Returns `true` if the environment is "relocatable".
+    pub fn relocatable(&self) -> bool {
+        self.cfg().is_ok_and(|cfg| cfg.is_relocatable())
+    }
+
     /// Returns the location of the Python executable.
     pub fn python_executable(&self) -> &Path {
         self.0.interpreter.sys_executable()

crates/uv-python/src/virtualenv.rs

@@ -28,6 +28,8 @@ pub struct PyVenvConfiguration {
     pub(crate) virtualenv: bool,
     /// If the uv package was used to create the virtual environment.
     pub(crate) uv: bool,
+    /// Is the virtual environment relocatable?
+    pub(crate) relocatable: bool,
 }
 
 #[derive(Debug, Error)]
@@ -136,14 +138,15 @@ impl PyVenvConfiguration {
     pub fn parse(cfg: impl AsRef<Path>) -> Result<Self, Error> {
         let mut virtualenv = false;
         let mut uv = false;
+        let mut relocatable = false;
 
         // Per https://snarky.ca/how-virtual-environments-work/, the `pyvenv.cfg` file is not a
         // valid INI file, and is instead expected to be parsed by partitioning each line on the
         // first equals sign.
         let content = fs::read_to_string(&cfg)
             .map_err(|err| Error::ParsePyVenvCfg(cfg.as_ref().to_path_buf(), err))?;
         for line in content.lines() {
-            let Some((key, _value)) = line.split_once('=') else {
+            let Some((key, value)) = line.split_once('=') else {
                 continue;
             };
             match key.trim() {
@@ -153,11 +156,18 @@ impl PyVenvConfiguration {
                 "uv" => {
                     uv = true;
                 }
+                "relocatable" => {
+                    relocatable = value.trim().to_lowercase() == "true";
+                }
                 _ => {}
             }
         }
 
-        Ok(Self { virtualenv, uv })
+        Ok(Self {
+            virtualenv,
+            uv,
+            relocatable,
+        })
     }
 
     /// Returns true if the virtual environment was created with the `virtualenv` package.
@@ -169,4 +179,9 @@ impl PyVenvConfiguration {
     pub fn is_uv(&self) -> bool {
         self.uv
     }
+
+    /// Returns true if the virtual environment is relocatable.
+    pub fn is_relocatable(&self) -> bool {
+        self.relocatable
+    }
 }

crates/uv-tool/src/lib.rs

@@ -258,6 +258,7 @@ impl InstalledTools {
             uv_virtualenv::Prompt::None,
             false,
             false,
+            false,
         )?;
 
         Ok(venv)