MNT: Always compile Cython at build time

MANIFEST.in

@@ -3,6 +3,6 @@ include LICENSE_Python.txt
 include README.rst
 include python25.pxd
 include timers.h
-include _line_profiler.c
+exclude _line_profiler.c
 include unset_trace.h
 recursive-include tests *.py

pyproject.toml

@@ -0,0 +1,6 @@
+[build-system]
+requires = [
+    "setuptools",
+    "wheel",
+    "cython"
+]

setup.py

@@ -1,4 +1,3 @@
-import os
 import sys
 
 # Monkeypatch distutils.
@@ -7,22 +6,16 @@
 import distutils.errors
 from distutils.core import setup
 from distutils.extension import Extension
-from distutils.log import warn
 
 try:
     from Cython.Distutils import build_ext
     cmdclass = dict(build_ext=build_ext)
     line_profiler_source = '_line_profiler.pyx'
 except ImportError:
-    cmdclass = {}
-    line_profiler_source = '_line_profiler.c'
-    if not os.path.exists(line_profiler_source):
-        raise distutils.errors.DistutilsError("""\
+    raise distutils.errors.DistutilsError("""\
 You need Cython to build the line_profiler from a git checkout, or
 alternatively use a release tarball from PyPI to build it without Cython.""")
-    else:
-        warn("Could not import Cython. "
-             "Using the available pre-generated C file.")
+
 
 long_description = """\
 line_profiler will profile the time individual lines of code take to execute.
@@ -78,6 +71,9 @@
             'kernprof=kernprof:main',
         ],
     },
+    setup_requires = [
+        'cython',
+    ],
     install_requires = [
         'IPython>=0.13',
     ],