Implement warning to make users aware of the missing check

We are not currently capable of checking Python version specifiers
from Poetry specification because it's very complex. And right now
it's better to warn users about it than do nothing.

micropipenv.py

@@ -640,11 +640,27 @@ def _translate_poetry_dependency(info):  # type: (str) -> str
 
 
 def _poetry2pipfile_lock(
-    only_direct=False, no_default=False, no_dev=False
-):  # type: (bool, bool, bool) -> Dict[str, Any]
+    only_direct=False,
+    no_default=False,
+    no_dev=False,
+    deploy=False,
+):  # type: (bool, bool, bool, bool) -> Dict[str, Any]
     """Convert Poetry files to Pipfile.lock as Pipenv would produce."""
     poetry_lock, pyproject_toml = _read_poetry()
 
+    # If deploy is specified, show a message about the lack of Python versions
+    # parsing capabilities in Micropipenv.
+    # TODO: Implement or use external parser for Python versions in Poetry specification.
+    # See for details: https://github.com/thoth-station/micropipenv/issues/187
+    current_python_version = "{}.{}".format(sys.version_info.major, sys.version_info.minor)
+    wanted_python_version = poetry_lock["metadata"]["python-versions"]
+    message = (
+        "Warning: Currently, Micropipenv is not able to parse complex Python version specifications used by Poetry. "
+        f"Desired version: {wanted_python_version}, current version: {current_python_version}."
+    )
+    level = "warn" if deploy else "debug"
+    getattr(_LOGGER, level)(message)
+
     pyproject_poetry_section = pyproject_toml.get("tool", {}).get("poetry", {})
 
     sources = []
@@ -680,7 +696,7 @@ def _poetry2pipfile_lock(
                 "hash": {"sha256": poetry_lock["metadata"]["content-hash"]},
                 "pipfile-spec": 6,
                 "sources": sources,
-                "requires": {"python_version": "{}.{}".format(sys.version_info.major, sys.version_info.minor)},
+                "requires": {"python_version": current_python_version},
             },
             "default": default,
             "develop": develop,
@@ -800,10 +816,12 @@ def _poetry2pipfile_lock(
     }
 
 
-def install_poetry(pip_bin=_PIP_BIN, *, dev=False, pip_args=None):  # type: (str, bool, Optional[List[str]]) -> None
+def install_poetry(
+    pip_bin=_PIP_BIN, *, deploy=False, dev=False, pip_args=None
+):  # type: (str, bool, bool, Optional[List[str]]) -> None
     """Install requirements from poetry.lock."""
     try:
-        pipfile_lock = _poetry2pipfile_lock()
+        pipfile_lock = _poetry2pipfile_lock(deploy=deploy)
     except KeyError as exc:
         raise PoetryError("Failed to parse poetry.lock and pyproject.toml: {}".format(str(exc))) from exc
     install_pipenv(pip_bin, pipfile_lock=pipfile_lock, pip_args=pip_args, dev=dev, deploy=False)
@@ -887,10 +905,7 @@ def install(
         install_pipenv(pip_bin, deploy=deploy, dev=dev, pip_args=pip_args)
         return
     elif method == "poetry":
-        if deploy:
-            _LOGGER.debug("Discarding deploy flag when poetry.lock is used")
-
-        install_poetry(pip_bin, pip_args=pip_args, dev=dev)
+        install_poetry(pip_bin, pip_args=pip_args, deploy=deploy, dev=dev)
         return
 
     raise MicropipenvException("Unhandled method for installing requirements: {}".format(method))