editable: use writable script dir for system env

This change ensures that, When using system environment, poetry falls
back to `userbase` if default location is not writable.

poetry/masonry/builders/editable.py

@@ -13,6 +13,7 @@
 from poetry.utils._compat import WINDOWS
 from poetry.utils._compat import Path
 from poetry.utils._compat import decode
+from poetry.utils.helpers import is_dir_writable
 
 
 SCRIPT_TEMPLATE = """\
@@ -128,7 +129,17 @@ def _add_pth(self):
     def _add_scripts(self):
         added = []
         entry_points = self.convert_entry_points()
-        scripts_path = Path(self._env.paths["scripts"])
+
+        for scripts_path in self._env.script_dirs:
+            if is_dir_writable(scripts_path):
+                break
+        else:
+            self._io.error_line(
+                "  - Failed to find a suitable script installation directory for {}".format(
+                    self._poetry.file.parent
+                )
+            )
+            return []
 
         scripts = entry_points.get("console_scripts", [])
         for script in scripts:
@@ -146,7 +157,7 @@ def _add_scripts(self):
                 f.write(
                     decode(
                         SCRIPT_TEMPLATE.format(
-                            python=self._env._bin("python"),
+                            python=self._env.python,
                             module=module,
                             callable_holder=callable_holder,
                             callable_=callable_,
@@ -160,9 +171,7 @@ def _add_scripts(self):
 
             if WINDOWS:
                 cmd_script = script_file.with_suffix(".cmd")
-                cmd = WINDOWS_CMD_TEMPLATE.format(
-                    python=self._env._bin("python"), script=name
-                )
+                cmd = WINDOWS_CMD_TEMPLATE.format(python=self._env.python, script=name)
                 self._debug(
                     "  - Adding the <c2>{}</c2> script wrapper to <b>{}</b>".format(
                         cmd_script.name, scripts_path

poetry/utils/env.py

@@ -7,7 +7,6 @@
 import shutil
 import sys
 import sysconfig
-import tempfile
 import textwrap
 
 from contextlib import contextmanager
@@ -40,6 +39,7 @@
 from poetry.utils._compat import encode
 from poetry.utils._compat import list_to_shell_command
 from poetry.utils._compat import subprocess
+from poetry.utils.helpers import is_dir_writable
 from poetry.utils.helpers import paths_csv
 
 
@@ -170,14 +170,9 @@ def writable_candidates(self):  # type: () -> List[Path]
 
         self._writable_candidates = []
         for candidate in self._candidates:
-            try:
-                if not candidate.exists():
-                    continue
-
-                with tempfile.TemporaryFile(dir=str(candidate)):
-                    self._writable_candidates.append(candidate)
-            except (IOError, OSError):
-                pass
+            if not is_dir_writable(candidate):
+                continue
+            self._writable_candidates.append(candidate)
 
         return self._writable_candidates
 
@@ -877,6 +872,7 @@ def __init__(self, path, base=None):  # type: (Path, Optional[Path]) -> None
         self._supported_tags = None
         self._purelib = None
         self._platlib = None
+        self._script_dirs = None
 
     @property
     def path(self):  # type: () -> Path
@@ -945,6 +941,11 @@ def usersite(self):  # type: () -> Optional[Path]
         if "usersite" in self.paths:
             return Path(self.paths["usersite"])
 
+    @property
+    def userbase(self):  # type: () -> Optional[Path]
+        if "userbase" in self.paths:
+            return Path(self.paths["userbase"])
+
     @property
     def purelib(self):  # type: () -> Path
         if self._purelib is None:
@@ -1091,6 +1092,18 @@ def execute(self, bin, *args, **kwargs):
     def is_venv(self):  # type: () -> bool
         raise NotImplementedError()
 
+    @property
+    def script_dirs(self):  # type: () -> List[Path]
+        if self._script_dirs is None:
+            self._script_dirs = (
+                [Path(self.paths["scripts"])]
+                if "scripts" in self.paths
+                else self._bin_dir
+            )
+            if self.userbase:
+                self._script_dirs.append(self.userbase / self._script_dirs[0].name)
+        return self._script_dirs
+
     def _bin(self, bin):  # type: (str) -> str
         """
         Return path to the given executable.
@@ -1126,6 +1139,10 @@ class SystemEnv(Env):
     A system (i.e. not a virtualenv) Python environment.
     """
 
+    @property
+    def python(self):  # type: () -> str
+        return sys.executable
+
     @property
     def sys_path(self):  # type: () -> List[str]
         return sys.path
@@ -1166,6 +1183,7 @@ def get_paths(self):  # type: () -> Dict[str, str]
 
         if site.check_enableusersite() and hasattr(obj, "install_usersite"):
             paths["usersite"] = getattr(obj, "install_usersite")
+            paths["userbase"] = getattr(obj, "install_userbase")
 
         return paths
 
@@ -1301,7 +1319,7 @@ def is_venv(self):  # type: () -> bool
 
     def is_sane(self):
         # A virtualenv is considered sane if both "python" and "pip" exist.
-        return os.path.exists(self._bin("python")) and os.path.exists(self._bin("pip"))
+        return os.path.exists(self.python) and os.path.exists(self._bin("pip"))
 
     def _run(self, cmd, **kwargs):
         with self.temp_environ():

poetry/utils/helpers.py

@@ -118,3 +118,18 @@ def get_package_version_display_string(
 
 def paths_csv(paths):  # type: (List[Path]) -> str
     return ", ".join('"{}"'.format(str(c)) for c in paths)
+
+
+def is_dir_writable(path, create=False):  # type: (Path, bool) -> bool
+    try:
+        if not path.exists():
+            if not create:
+                return False
+            path.mkdir(parents=True, exist_ok=True)
+
+        with tempfile.TemporaryFile(dir=str(path)):
+            pass
+    except (IOError, OSError):
+        return False
+    else:
+        return True