inspection: use pep517.meta.build from shell

With change we execute pep517 metadata build from within a new venv
retaining old `python setup.py egg_info` behaviour. We fallback to the
old behaviour if pep517 metadata build fails.

poetry/inspection/info.py

@@ -1,6 +1,6 @@
 import glob
 import logging
-import subprocess
+import os
 import tarfile
 import zipfile
 
@@ -12,8 +12,6 @@
 
 import pkginfo
 
-from pep517.build import compat_system as pep517_compat_system
-from pep517.meta import build as pep517_metadata_build
 from poetry.core.factory import Factory
 from poetry.core.packages import Package
 from poetry.core.packages import ProjectPackage
@@ -23,12 +21,26 @@
 from poetry.core.utils.helpers import parse_requires
 from poetry.core.utils.helpers import temporary_directory
 from poetry.core.version.markers import InvalidMarker
+from poetry.utils.env import EnvCommandError
+from poetry.utils.env import EnvManager
+from poetry.utils.env import VirtualEnv
 from poetry.utils.setup_reader import SetupReader
 from poetry.utils.toml_file import TomlFile
 
 
 logger = logging.getLogger(__name__)
 
+PEP517_META_BUILD = """\
+import pep517.build
+import pep517.meta
+
+path='{source}'
+system=pep517.build.compat_system(path)
+pep517.meta.build(source_dir=path, dest='{dest}', system=system)
+"""
+
+PEP517_META_BUILD_DEPS = ["pep517===0.8.2", "toml==0.10.1"]
+
 
 class PackageInfoError(ValueError):
     def __init__(self, path):  # type: (Union[Path, str]) -> None
@@ -255,6 +267,10 @@ def _from_sdist_file(cls, path):  # type: (Path) -> PackageInfo
 
         return info.update(new_info)
 
+    @staticmethod
+    def has_setup_files(path):  # type: (Path) -> bool
+        return any((path / f).exists() for f in SetupReader.FILES)
+
     @classmethod
     def from_setup_files(cls, path):  # type: (Path) -> PackageInfo
         """
@@ -264,7 +280,7 @@ def from_setup_files(cls, path):  # type: (Path) -> PackageInfo
 
         :param path: Path to `setup.py` file
         """
-        if not any((path / f).exists() for f in SetupReader.FILES):
+        if not cls.has_setup_files(path):
             raise PackageInfoError(path)
 
         try:
@@ -416,21 +432,56 @@ def _pep517_metadata(cls, path):  # type (Path) -> PackageInfo
         except PackageInfoError:
             pass
 
-        try:
-            with temporary_directory() as tmp_dir:
-                pep517_metadata_build(
-                    source_dir=path.as_posix(),
-                    dest=tmp_dir,
-                    system=pep517_compat_system(source_dir=path.as_posix()),
+        with temporary_directory() as tmp_dir:
+            # TODO: cache PEP 517 build environment corresponding to each project venv
+            venv_dir = Path(tmp_dir) / ".venv"
+            EnvManager.build_venv(venv_dir.as_posix())
+            venv = VirtualEnv(venv_dir, venv_dir)
+
+            dest_dir = Path(tmp_dir) / "dist"
+            dest_dir.mkdir()
+
+            try:
+                venv.run(
+                    "python",
+                    "-m",
+                    "pip",
+                    "install",
+                    "--disable-pip-version-check",
+                    "--ignore-installed",
+                    *PEP517_META_BUILD_DEPS
                 )
-                return cls.from_metadata(Path(tmp_dir))
-        except subprocess.CalledProcessError:
-            cls._log("PEP 517 metadata build failed for {}".format(path), "debug")
-            if info:
-                cls._log(
-                    "Falling back to parsed setup.py file for {}".format(path), "debug"
+                venv.run(
+                    "python",
+                    "-",
+                    input_=PEP517_META_BUILD.format(
+                        source=path.as_posix(), dest=dest_dir.as_posix()
+                    ),
                 )
-                return info
+                return cls.from_metadata(dest_dir)
+            except EnvCommandError as e:
+                # something went wrong while attempting pep517 metadata build
+                # fallback to egg_info if setup.py available
+                cls._log("PEP517 build failed: {}".format(e), level="debug")
+                setup_py = path / "setup.py"
+                if not setup_py.exists():
+                    raise PackageInfoError(path)
+
+                cwd = Path.cwd()
+                os.chdir(path.as_posix())
+                try:
+                    venv.run("python", "setup.py", "egg_info")
+                    return cls.from_metadata(path)
+                except EnvCommandError:
+                    raise PackageInfoError(path)
+                finally:
+                    os.chdir(cwd.as_posix())
+
+        if info:
+            cls._log(
+                "Falling back to parsed setup.py file for {}".format(path), "debug"
+            )
+            return info
 
         # if we reach here, everything has failed and all hope is lost
         raise PackageInfoError(path)

pyproject.toml

@@ -60,7 +60,6 @@ keyring = [
 # Use subprocess32 for Python 2.7
 subprocess32 = { version = "^3.5", python = "~2.7" }
 importlib-metadata = {version = "^1.6.0", python = "<3.8"}
-pep517 = "^0.8.2"
 
 [tool.poetry.dev-dependencies]
 pytest = [