Fix pip in shell for uv/virtualenv-based python

pkgs/modules/python/default.nix

@@ -162,7 +162,7 @@ in
     POETRY_USE_USER_SITE = "1";
     PIP_CONFIG_FILE = pip.config.outPath;
     PYTHONUSERBASE = userbase;
-    PYTHONPATH = "${sitecustomize}:${pip.pip}/${python.sitePackages}";
+    PYTHONPATH = "${sitecustomize}:${pip.sitePackages}";
     REPLIT_PYTHONPATH = "${userbase}/${python.sitePackages}:${pypkgs.setuptools}/${python.sitePackages}";
     UV_PROJECT_ENVIRONMENT = "$REPL_HOME/.pythonlibs";
     UV_PYTHON_DOWNLOADS = "never";

pkgs/modules/python/pip.nix

@@ -1,4 +1,4 @@
-pkgs @ { pypkgs, ... }:
+pkgs @ { pypkgs, python, ... }:
 
 let
   pip = pypkgs.pip.overridePythonAttrs (old: rec {
@@ -18,6 +18,41 @@ let
     ];
   });
 
+  # This pip wrapper will detect if python is called from within
+  # the virtualenv: `.pythonlibs/bin`. If so, it will install a shell script
+  # called `pip` into the virtualenv so that if pip is called in the future
+  # python will think it's in the virtualenv.
+  pip-wrapper = pkgs.writeShellApplication {
+    name = "pip";
+    text = ''
+      python_location=$(which python)
+      venv_pip_location="''${REPL_HOME}/.pythonlibs/bin/pip"
+      venv_pip3_location="''${REPL_HOME}/.pythonlibs/bin/pip3"
+
+      function init_venv_pip {
+        cat <<EOF > "''${venv_pip_location}"
+      #! /bin/sh
+      export PIP_CONFIG_FILE=
+      python -m pip "\$@"
+      EOF
+        chmod u+x "''${venv_pip_location}"
+        if [ ! -f "''${venv_pip3_location}" ]; then
+          ln -s "''${venv_pip_location}" "''${venv_pip3_location}"
+        fi
+      }
+
+      if [ "$python_location" = "''${REPL_HOME}/.pythonlibs/bin/python" ]; then
+        if [ ! -f "''${venv_pip_location}" ]; then
+          init_venv_pip
+        fi
+        exec "''${venv_pip_location}" "$@"
+      else
+        unset PYTHONNOUSERSITE
+        exec "${pip}/bin/pip"  "$@" 
+      fi
+    '';
+  };
+
   config = pkgs.writeTextFile {
     name = "pip.conf";
     text = ''
@@ -29,5 +64,7 @@ let
   };
 in
 {
-  inherit pip config;
+  pip = pip-wrapper;
+  sitePackages = "${pip}/${python.sitePackages}";
+  inherit config;
 }

pkgs/python-wrapped/main.go

@@ -4,6 +4,8 @@ import (
 	"os"
 	"strings"
 	"syscall"
+	"fmt"
+	"path/filepath"
 )
 
 var PythonExePath string
@@ -39,6 +41,22 @@ func legacy() {
 	}
 }
 
+// Unsets the PIP_CONFIG_FILE config if we are running in virtualenv mode,
+// because that config file - see pip.nix - works only for `--user` mode pip installs
+// but pip cannot do `--user` inside virtualenv.
+func unsetPipConfigFileForVirtualEnvPython() {
+    var exePath, err = filepath.Abs(os.Args[0])
+    if err == nil {
+        repl_home := os.Getenv("REPL_HOME")
+        if repl_home != "" {
+            dot_python_dir := fmt.Sprintf("%s/%s", repl_home, ".pythonlibs/bin/")
+            if strings.HasPrefix(exePath, dot_python_dir) {
+                os.Unsetenv("PIP_CONFIG_FILE")
+            }
+        }
+    }
+}
+
 // Set up environment for non-legacy nixpkgs
 func modern() {
 	if ldAudit := os.Getenv("REPLIT_LD_AUDIT"); ldAudit != "" {
@@ -65,6 +83,7 @@ func channelWorksWithRtldLoader(channel string) bool {
 }
 
 func main() {
+	unsetPipConfigFileForVirtualEnvPython()
 	os.Unsetenv("PYTHONNOUSERSITE")
 
 	if val, ok := os.LookupEnv("REPLIT_NIX_CHANNEL"); ok && channelWorksWithRtldLoader(val) {