fix(venv): make relocatable activation scripts support ksh

It transpires that detecting the directory a script was sourced from
is non-trivial across `bash`, `ksh` and `zsh`.

The previous version was a one-liner and supported `bash` and `zsh` but
not `ksh`.

It is possible to keep the one-liner and add `ksh` support, but that
is mutually-exclusive with `zsh`.

Therefore, the only way to square this circle is to add an `if` block.
A silver lining here is that although longer, the script is probably
easier to follow as there is less code-golfing going on.

crates/uv-virtualenv/src/activator/activate

@@ -22,10 +22,18 @@
 # This file must be used with "source bin/activate" *from bash*
 # you cannot run it directly
 
-
-if [ "${BASH_SOURCE-}" = "$0" ]; then
-    echo "You must source this script: \$ source $0" >&2
-    exit 33
+# Get script path (only used if environment is relocatable).
+if [ -n "${BASH_VERSION:+x}" ] ; then
+    SCRIPT_PATH="${BASH_SOURCE[0]}"
+    if [ "$SCRIPT_PATH" = "$0" ]; then
+        # Only bash has a reasonably robust check for source'dness.
+        echo "You must source this script: \$ source $0" >&2
+        exit 33
+    fi
+elif [ -n "${ZSH_VERSION:+x}" ] ; then
+    SCRIPT_PATH="${(%):-%x}"
+elif [ -n "${KSH_VERSION:+x}" ] ; then
+    SCRIPT_PATH="${.sh.file}"
 fi
 
 deactivate () {

crates/uv-virtualenv/src/virtualenv.rs

@@ -299,7 +299,7 @@ pub(crate) fn create(
             (true, "activate") => {
                 // Extremely verbose, but should cover all major POSIX shells,
                 // as well as platforms where `readlink` does not implement `-f`.
-                r#"'"$(dirname -- "$(CDPATH= cd -- "$(dirname -- ${BASH_SOURCE[0]:-${(%):-%x}})" && echo "$PWD")")"'"#
+                r#"'"$(dirname -- "$(CDPATH= cd -- "$(dirname -- "$SCRIPT_PATH")" && echo "$PWD")")"'"#
             }
             (true, "activate.bat") => r"%~dp0..",
             (true, "activate.fish") => {

crates/uv/tests/venv.rs

@@ -615,7 +615,7 @@ fn verify_pyvenv_cfg_relocatable() {
 
     let activate_sh = scripts.child("activate");
     activate_sh.assert(predicates::path::is_file());
-    activate_sh.assert(predicates::str::contains(r#"VIRTUAL_ENV=''"$(dirname -- "$(CDPATH= cd -- "$(dirname -- ${BASH_SOURCE[0]:-${(%):-%x}})" && echo "$PWD")")"''"#));
+    activate_sh.assert(predicates::str::contains(r#"VIRTUAL_ENV=''"$(dirname -- "$(CDPATH= cd -- "$(dirname -- "$SCRIPT_PATH")" && echo "$PWD")")"''"#));
 
     let activate_bat = scripts.child("activate.bat");
     activate_bat.assert(predicates::path::is_file());