Fail with a helpful message if separate cache is not supported (#186)

* Add Julia._unbox_as

* Fail with a helpful message if separate cache is not supported

* Emit different message when statically linked

* Rename: test_utils.py -> test_find_libpython.py

* Test raise_separate_cache_error

julia/core.py

@@ -351,8 +351,84 @@ def is_compatible_exe(jlinfo, _debug=lambda *_: None):
     return py_libpython == jl_libpython
 
 
+_separate_cache_error_common_header = """\
+It seems your Julia and PyJulia setup are not supported.
+
+Julia interpreter:
+    {runtime}
+Python interpreter and libpython used by PyCall.jl:
+    {jlinfo.pyprogramname}
+    {jl_libpython}
+Python interpreter used to import PyJulia and its libpython.
+    {sys.executable}
+    {py_libpython}
+"""
+
+
+_separate_cache_error_common_footer = """
+For more information, see:
+    https://github.com/JuliaPy/pyjulia
+    https://github.com/JuliaPy/PyCall.jl
+"""
+
+
+_separate_cache_error_statically_linked = """
+Your Python interpreter "{sys.executable}"
+is statically linked to libpython.  Currently, PyJulia does not support
+such Python interpreter.  For available workarounds, see:
+    https://github.com/JuliaPy/pyjulia/issues/185
+"""
+
+
+_separate_cache_error_incompatible_libpython = """
+In Julia >= 0.7, above two paths to `libpython` have to match exactly
+in order for PyJulia to work.  To configure PyCall.jl to use Python
+interpreter "{sys.executable}",
+run the following commands in the Julia interpreter:
+
+    ENV["PYTHON"] = "{sys.executable}"
+    using Pkg
+    Pkg.build("PyCall")
+"""
+
+
+def raise_separate_cache_error(
+        runtime, jlinfo,
+        # For test:
+        _determine_if_statically_linked=determine_if_statically_linked):
+    template = _separate_cache_error_common_header
+    if _determine_if_statically_linked():
+        template += _separate_cache_error_statically_linked
+    else:
+        template += _separate_cache_error_incompatible_libpython
+    template += _separate_cache_error_common_footer
+    message = template.format(
+        runtime=runtime,
+        jlinfo=jlinfo,
+        py_libpython=find_libpython(),
+        jl_libpython=normalize_path(jlinfo.libpython),
+        sys=sys)
+    raise RuntimeError(message)
+
+
 _julia_runtime = [False]
 
+
+UNBOXABLE_TYPES = (
+    'bool',
+    'int8',
+    'uint8',
+    'int16',
+    'uint16',
+    'int32',
+    'uint32',
+    'int64',
+    'uint64',
+    'float32',
+    'float64',
+)
+
+
 class Julia(object):
     """
     Implements a bridge to the Julia interpreter or library.
@@ -483,6 +559,17 @@ def __init__(self, init_julia=True, jl_init_path=None, runtime=None,
         self.api.jl_unbox_voidpointer.argtypes = [void_p]
         self.api.jl_unbox_voidpointer.restype = py_object
 
+        for c_type in UNBOXABLE_TYPES:
+            jl_unbox = getattr(self.api, "jl_unbox_{}".format(c_type))
+            jl_unbox.argtypes = [void_p]
+            jl_unbox.restype = getattr(ctypes, "c_{}".format({
+                "float32": "float",
+                "float64": "double",
+            }.get(c_type, c_type)))
+
+        self.api.jl_typeof.argtypes = [void_p]
+        self.api.jl_typeof.restype = void_p
+
         self.api.jl_exception_clear.restype = None
         self.api.jl_stderr_obj.argtypes = []
         self.api.jl_stderr_obj.restype = void_p
@@ -494,14 +581,20 @@ def __init__(self, init_julia=True, jl_init_path=None, runtime=None,
         if init_julia:
             if use_separate_cache:
                 # First check that this is supported
-                self._call("""
-                    if VERSION < v"0.5-"
-                        error(\"""Using pyjulia with a statically-compiled version
-                                  of python or with a version of python that
-                                  differs from that used by PyCall.jl is not
-                                  supported on julia 0.4""\")
-                    end
-                """)
+                version_range = self._unbox_as(self._call("""
+                Int64(if VERSION < v"0.6-"
+                    2
+                elseif VERSION >= v"0.7-"
+                    1
+                else
+                    0
+                end)
+                """), "int64")
+                if version_range == 2:
+                    raise RuntimeError(
+                        "PyJulia does not support Julia < 0.6 anymore")
+                elif version_range == 1:
+                    raise_separate_cache_error(runtime, jlinfo)
                 # Intercept precompilation
                 os.environ["PYCALL_PYTHON_EXE"] = sys.executable
                 os.environ["PYCALL_JULIA_HOME"] = PYCALL_JULIA_HOME
@@ -580,6 +673,29 @@ def _call(self, src):
 
         return ans
 
+    @staticmethod
+    def _check_unboxable(c_type):
+        if c_type not in UNBOXABLE_TYPES:
+            raise ValueError("Julia value cannot be unboxed as c_type={!r}.\n"
+                             "c_type supported by PyJulia are:\n"
+                             "{}".format(c_type, "\n".join(UNBOXABLE_TYPES)))
+
+    def _is_unboxable_as(self, pointer, c_type):
+        self._check_unboxable(c_type)
+        jl_type = getattr(self.api, 'jl_{}_type'.format(c_type))
+        desired = ctypes.cast(jl_type, ctypes.POINTER(ctypes.c_void_p))[0]
+        actual = self.api.jl_typeof(pointer)
+        return actual == desired
+
+    def _unbox_as(self, pointer, c_type):
+        self._check_unboxable(c_type)
+        jl_unbox = getattr(self.api, 'jl_unbox_{}'.format(c_type))
+        if self._is_unboxable_as(pointer, c_type):
+            return jl_unbox(pointer)
+        else:
+            raise TypeError("Cannot unbox pointer {} as {}"
+                            .format(pointer, c_type))
+
     def check_exception(self, src="<unknown code>"):
         exoc = self.api.jl_exception_occurred()
         self._debug("exception occured? " + str(exoc))

test/test_find_libpython.py

@@ -0,0 +1,25 @@
+import platform
+
+import pytest
+
+from julia.find_libpython import finding_libpython, linked_libpython
+from julia.core import determine_if_statically_linked
+
+try:
+    unicode
+except NameError:
+    unicode = str  # for Python 3
+
+
+def test_finding_libpython_yield_type():
+    paths = list(finding_libpython())
+    assert set(map(type, paths)) <= {str, unicode}
+# In a statically linked Python executable, no paths may be found.  So
+# let's just check returned type of finding_libpython.
+
+
+@pytest.mark.xfail(platform.system() == "Windows",
+                   reason="linked_libpython is not implemented for Windows")
+def test_linked_libpython():
+    if determine_if_statically_linked():
+        assert linked_libpython() is not None

test/test_utils.py

@@ -2,28 +2,41 @@
 Unit tests which can be done without loading `libjulia`.
 """
 
-import platform
+import os
 
 import pytest
 
-from julia.find_libpython import finding_libpython, linked_libpython
-from julia.core import determine_if_statically_linked
+from julia.core import raise_separate_cache_error
 
 try:
-    unicode
-except NameError:
-    unicode = str  # for Python 3
-
-
-def test_finding_libpython_yield_type():
-    paths = list(finding_libpython())
-    assert set(map(type, paths)) <= {str, unicode}
-# In a statically linked Python executable, no paths may be found.  So
-# let's just check returned type of finding_libpython.
-
-
-@pytest.mark.xfail(platform.system() == "Windows",
-                   reason="linked_libpython is not implemented for Windows")
-def test_linked_libpython():
-    if determine_if_statically_linked():
-        assert linked_libpython() is not None
+    from types import SimpleNamespace
+except ImportError:
+    from argparse import Namespace as SimpleNamespace  # Python 2
+
+
+def dummy_juliainfo():
+    somepath = os.devnull  # some random path
+    return SimpleNamespace(
+        pyprogramname=somepath,
+        libpython=somepath,
+    )
+
+
+def test_raise_separate_cache_error_statically_linked():
+    runtime = "julia"
+    jlinfo = dummy_juliainfo()
+    with pytest.raises(RuntimeError) as excinfo:
+        raise_separate_cache_error(
+            runtime, jlinfo,
+            _determine_if_statically_linked=lambda: True)
+    assert "is statically linked" in str(excinfo.value)
+
+
+def test_raise_separate_cache_error_dynamically_linked():
+    runtime = "julia"
+    jlinfo = dummy_juliainfo()
+    with pytest.raises(RuntimeError) as excinfo:
+        raise_separate_cache_error(
+            runtime, jlinfo,
+            _determine_if_statically_linked=lambda: False)
+    assert "have to match exactly" in str(excinfo.value)