Fix venv creation in Python environments

The way we build python environments is subtly broken. A python
environment should be semantically identical to a vanilla Python
installation in, say, /usr/local. The current implementation, however,
differs in two important ways. The first is that it's impossible to use
python packages from the environment in python virtual environments. The
second is that the nix-generated environment appears to be a venv, but
it's not.

This commit changes the way python environments are built:

  * When generating wrappers for python executables, we inherit argv[0]
    from the wrapper. This causes python to initialize its configuration
    in the environment with all the correct paths.
  * We remove the sitecustomize.py file from the base python package.
    This file was used tweak the python configuration after it was
    incorrectly initialized. That's no longer necessary.

The end result is that python environments no longer appear to be venvs,
and behave more like a vanilla python installation. In addition it's
possible to create a venv using an environment and use packages from
both the environment and the venv.

pkgs/build-support/setup-hooks/make-binary-wrapper/make-binary-wrapper.sh

@@ -19,6 +19,7 @@ assertExecutable() {
 #                          (if unset or empty, defaults to EXECUTABLE)
 # --inherit-argv0        : the executable inherits argv0 from the wrapper.
 #                          (use instead of --argv0 '$0')
+# --resolve-argv0        : if argv0 doesn't include a / character, resolve it against PATH
 # --set          VAR VAL : add VAR with value VAL to the executable's environment
 # --set-default  VAR VAL : like --set, but only adds VAR if not already set in
 #                          the environment
@@ -87,6 +88,7 @@ makeDocumentedCWrapper() {
 makeCWrapper() {
     local argv0 inherit_argv0 n params cmd main flagsBefore flagsAfter flags executable length
     local uses_prefix uses_suffix uses_assert uses_assert_success uses_stdio uses_asprintf
+    local resolve_path
     executable=$(escapeStringLiteral "$1")
     params=("$@")
     length=${#params[*]}
@@ -169,23 +171,32 @@ makeCWrapper() {
                 # Whichever comes last of --argv0 and --inherit-argv0 wins
                 inherit_argv0=1
             ;;
+            --resolve-argv0)
+                # this gets processed after other argv0 flags
+                uses_stdio=1
+                uses_string=1
+                resolve_argv0=1
+            ;;
             *) # Using an error macro, we will make sure the compiler gives an understandable error message
                 main="$main#error makeCWrapper: Unknown argument ${p}"$'\n'
             ;;
         esac
     done
     [[ -z "$flagsBefore" && -z "$flagsAfter" ]] || main="$main"${main:+$'\n'}$(addFlags "$flagsBefore" "$flagsAfter")$'\n'$'\n'
     [ -z "$inherit_argv0" ] && main="${main}argv[0] = \"${argv0:-${executable}}\";"$'\n'
+    [ -z "$resolve_argv0" ] || main="${main}argv[0] = resolve_argv0(argv[0]);"$'\n'
     main="${main}return execv(\"${executable}\", argv);"$'\n'
 
     [ -z "$uses_asprintf" ] || printf '%s\n' "#define _GNU_SOURCE         /* See feature_test_macros(7) */"
     printf '%s\n' "#include <unistd.h>"
     printf '%s\n' "#include <stdlib.h>"
     [ -z "$uses_assert" ]   || printf '%s\n' "#include <assert.h>"
     [ -z "$uses_stdio" ]    || printf '%s\n' "#include <stdio.h>"
+    [ -z "$uses_string" ]   || printf '%s\n' "#include <string.h>"
     [ -z "$uses_assert_success" ] || printf '\n%s\n' "#define assert_success(e) do { if ((e) < 0) { perror(#e); abort(); } } while (0)"
     [ -z "$uses_prefix" ] || printf '\n%s\n' "$(setEnvPrefixFn)"
     [ -z "$uses_suffix" ] || printf '\n%s\n' "$(setEnvSuffixFn)"
+    [ -z "$resolve_argv0" ] || printf '\n%s\n' "$(resolveArgv0Fn)"
     printf '\n%s' "int main(int argc, char **argv) {"
     printf '\n%s' "$(indent4 "$main")"
     printf '\n%s\n' "}"
@@ -338,6 +349,41 @@ void set_env_suffix(char *env, char *sep, char *suffix) {
 "
 }
 
+resolveArgv0Fn() {
+  printf '%s' "\
+char *resolve_argv0(char *argv0) {
+  if (strchr(argv0, '/') != NULL) {
+    return argv0;
+  }
+  char *path = getenv(\"PATH\");
+  if (path == NULL) {
+    return argv0;
+  }
+  char *path_copy = strdup(path);
+  if (path_copy == NULL) {
+    return argv0;
+  }
+  char *dir = strtok(path_copy, \":\");
+  while (dir != NULL) {
+    char *candidate = malloc(strlen(dir) + strlen(argv0) + 2);
+    if (candidate == NULL) {
+      free(path_copy);
+      return argv0;
+    }
+    sprintf(candidate, \"%s/%s\", dir, argv0);
+    if (access(candidate, X_OK) == 0) {
+      free(path_copy);
+      return candidate;
+    }
+    free(candidate);
+    dir = strtok(NULL, \":\");
+  }
+  free(path_copy);
+  return argv0;
+}
+"
+}
+
 # Embed a C string which shows up as readable text in the compiled binary wrapper,
 # giving instructions for recreating the wrapper.
 # Keep in sync with makeBinaryWrapper.extractCmd

pkgs/build-support/setup-hooks/make-wrapper.sh

@@ -15,6 +15,7 @@ assertExecutable() {
 #                          (if unset or empty, defaults to EXECUTABLE)
 # --inherit-argv0        : the executable inherits argv0 from the wrapper.
 #                          (use instead of --argv0 '$0')
+# --resolve-argv0        : if argv0 doesn't include a / character, resolve it against PATH
 # --set          VAR VAL : add VAR with value VAL to the executable's environment
 # --set-default  VAR VAL : like --set, but only adds VAR if not already set in
 #                          the environment
@@ -177,6 +178,9 @@ makeShellWrapper() {
         elif [[ "$p" == "--inherit-argv0" ]]; then
             # Whichever comes last of --argv0 and --inherit-argv0 wins
             argv0='$0'
+        elif [[ "$p" == "--resolve-argv0" ]]; then
+            # this is noop in shell wrappers, since bash will always resolve $0
+            resolve_argv0=1
         else
             die "makeWrapper doesn't understand the arg $p"
         fi

pkgs/development/interpreters/python/cpython/2.7/default.nix

@@ -318,8 +318,6 @@ in with passthru; stdenv.mkDerivation ({
     inherit passthru;
 
     postFixup = ''
-      # Include a sitecustomize.py file. Note it causes an error when it's in postInstall with 2.7.
-      cp ${../../sitecustomize.py} $out/${sitePackages}/sitecustomize.py
     '' + lib.optionalString strip2to3 ''
       rm -R $out/bin/2to3 $out/lib/python*/lib2to3
     '' + lib.optionalString stripConfig ''

pkgs/development/interpreters/python/cpython/default.nix

@@ -530,8 +530,7 @@ in with passthru; stdenv.mkDerivation (finalAttrs: {
     # Strip tests
     rm -R $out/lib/python*/test $out/lib/python*/**/test{,s}
     '' + optionalString includeSiteCustomize ''
-    # Include a sitecustomize.py file
-    cp ${../sitecustomize.py} $out/${sitePackages}/sitecustomize.py
+
     '' + optionalString stripBytecode ''
     # Determinism: deterministic bytecode
     # First we delete all old bytecode.

pkgs/development/interpreters/python/pypy/default.nix

@@ -126,9 +126,6 @@ in with passthru; stdenv.mkDerivation rec {
     ln -s $out/${executable}-c/include $out/include/${libPrefix}
     ln -s $out/${executable}-c/lib-python/${if isPy3k then "3" else pythonVersion} $out/lib/${libPrefix}
 
-    # Include a sitecustomize.py file
-    cp ${../sitecustomize.py} $out/${if isPy38OrNewer then sitePackages else "lib/${libPrefix}/${sitePackages}"}/sitecustomize.py
-
     runHook postInstall
   '';
 

pkgs/development/interpreters/python/pypy/prebuilt.nix

@@ -95,9 +95,6 @@ in with passthru; stdenv.mkDerivation {
     echo "Removing bytecode"
     find . -name "__pycache__" -type d -depth -delete
 
-    # Include a sitecustomize.py file
-    cp ${../sitecustomize.py} $out/${sitePackages}/sitecustomize.py
-
     runHook postInstall
   '';
 

pkgs/development/interpreters/python/pypy/prebuilt_2_7.nix

@@ -96,9 +96,6 @@ in with passthru; stdenv.mkDerivation {
     echo "Removing bytecode"
     find . -name "__pycache__" -type d -depth -delete
 
-    # Include a sitecustomize.py file
-    cp ${../sitecustomize.py} $out/${sitePackages}/sitecustomize.py
-
     runHook postInstall
   '';
 

pkgs/development/interpreters/python/tests.nix

@@ -39,11 +39,21 @@ let
         is_virtualenv = "False";
       };
     } // lib.optionalAttrs (!python.isPyPy) {
-      # Use virtualenv from a Nix env.
-      nixenv-virtualenv = rec {
-        env = runCommand "${python.name}-virtualenv" {} ''
-          ${pythonVirtualEnv.interpreter} -m virtualenv venv
-          mv venv $out
+      # Use virtualenv with symlinks from a Nix env.
+      nixenv-virtualenv-links = rec {
+        env = runCommand "${python.name}-virtualenv-links" {} ''
+          ${pythonVirtualEnv.interpreter} -m virtualenv --system-site-packages --symlinks --no-seed $out
+        '';
+        interpreter = "${env}/bin/${python.executable}";
+        is_venv = "False";
+        is_nixenv = "True";
+        is_virtualenv = "True";
+      };
+    } // lib.optionalAttrs (!python.isPyPy) {
+      # Use virtualenv with copies from a Nix env.
+      nixenv-virtualenv-copies = rec {
+        env = runCommand "${python.name}-virtualenv-copies" {} ''
+          ${pythonVirtualEnv.interpreter} -m virtualenv --system-site-packages --copies --no-seed $out
         '';
         interpreter = "${env}/bin/${python.executable}";
         is_venv = "False";
@@ -59,27 +69,48 @@ let
         is_nixenv = "True";
         is_virtualenv = "False";
       };
-    } // lib.optionalAttrs (python.isPy3k && (!python.isPyPy)) {
-      # Venv built using plain Python
+    } // lib.optionalAttrs (python.pythonAtLeast "3.8" && (!python.isPyPy)) {
+      # Venv built using links to plain Python
       # Python 2 does not support venv
       # TODO: PyPy executable name is incorrect, it should be pypy-c or pypy-3c instead of pypy and pypy3.
-      plain-venv = rec {
-        env = runCommand "${python.name}-venv" {} ''
-          ${python.interpreter} -m venv $out
+      plain-venv-links = rec {
+        env = runCommand "${python.name}-venv-links" {} ''
+          ${python.interpreter} -m venv --system-site-packages --symlinks --without-pip $out
+        '';
+        interpreter = "${env}/bin/${python.executable}";
+        is_venv = "True";
+        is_nixenv = "False";
+        is_virtualenv = "False";
+      };
+    } // lib.optionalAttrs (python.pythonAtLeast "3.8" && (!python.isPyPy)) {
+      # Venv built using copies from plain Python
+      # Python 2 does not support venv
+      # TODO: PyPy executable name is incorrect, it should be pypy-c or pypy-3c instead of pypy and pypy3.
+      plain-venv-copies = rec {
+        env = runCommand "${python.name}-venv-copies" {} ''
+          ${python.interpreter} -m venv --system-site-packages --copies --without-pip $out
         '';
         interpreter = "${env}/bin/${python.executable}";
         is_venv = "True";
         is_nixenv = "False";
         is_virtualenv = "False";
       };
-
     } // lib.optionalAttrs (python.pythonAtLeast "3.8") {
       # Venv built using Python Nix environment (python.buildEnv)
-      # TODO: Cannot create venv from a  nix env
-      # Error: Command '['/nix/store/ddc8nqx73pda86ibvhzdmvdsqmwnbjf7-python3-3.7.6-venv/bin/python3.7', '-Im', 'ensurepip', '--upgrade', '--default-pip']' returned non-zero exit status 1.
-      nixenv-venv = rec {
-        env = runCommand "${python.name}-venv" {} ''
-          ${pythonEnv.interpreter} -m venv $out
+      nixenv-venv-links = rec {
+        env = runCommand "${python.name}-venv-links" {} ''
+          ${pythonEnv.interpreter} -m venv --system-site-packages --symlinks --without-pip $out
+        '';
+        interpreter = "${env}/bin/${pythonEnv.executable}";
+        is_venv = "True";
+        is_nixenv = "True";
+        is_virtualenv = "False";
+      };
+    } // lib.optionalAttrs (python.pythonAtLeast "3.8") {
+      # Venv built using Python Nix environment (python.buildEnv)
+      nixenv-venv-copies = rec {
+        env = runCommand "${python.name}-venv-copies" {} ''
+          ${pythonEnv.interpreter} -m venv --system-site-packages --copies --without-pip $out
         '';
         interpreter = "${env}/bin/${pythonEnv.executable}";
         is_venv = "True";
@@ -91,11 +122,33 @@ let
     testfun = name: attrs: runCommand "${python.name}-tests-${name}" ({
       inherit (python) pythonVersion;
     } // attrs) ''
+      mkdir $out
+
+      # set up the test files
       cp -r ${./tests/test_environments} tests
       chmod -R +w tests
       substituteAllInPlace tests/test_python.py
-      ${attrs.interpreter} -m unittest discover --verbose tests #/test_python.py
-      mkdir $out
+
+      # run the tests by invoking the interpreter via full path
+      echo "absolute path: ${attrs.interpreter}"
+      ${attrs.interpreter} -m unittest discover --verbose tests 2>&1 | tee "$out/full.txt"
+
+      # run the tests by invoking the interpreter via $PATH
+      export PATH="$(dirname ${attrs.interpreter}):$PATH"
+      echo "PATH: $(basename ${attrs.interpreter})"
+      "$(basename ${attrs.interpreter})" -m unittest discover --verbose tests 2>&1 | tee "$out/path.txt"
+
+      # make sure we get the right path when invoking through a result link
+      ln -s "${attrs.env}" result
+      relative="result/bin/$(basename ${attrs.interpreter})"
+      expected="$PWD/$relative"
+      actual="$(./$relative -c "import sys; print(sys.executable)" | tee "$out/result.txt")"
+      if [ "$actual" != "$expected" ]; then
+        echo "expected $expected, got $actual"
+        exit 1
+      fi
+
+      # if we got this far, the tests passed
       touch $out/success
     '';
 

pkgs/development/interpreters/python/tests/test_environments/test_python.py

@@ -38,7 +38,7 @@ def test_site_prefix(self):
 
     @unittest.skipIf(IS_PYPY or sys.version_info.major==2, "Python 2 does not have base_prefix")
     def test_base_prefix(self):
-        if IS_VENV or IS_NIXENV or IS_VIRTUALENV:
+        if IS_VENV or IS_VIRTUALENV:
             self.assertNotEqual(sys.prefix, sys.base_prefix)
         else:
             self.assertEqual(sys.prefix, sys.base_prefix)