Add requirement parsing in setuptools.build_meta

This fixes GH #1682 by porting the pkg_resources requirement parsing
logic into setuptools.build_meta, so that all valid requirement
specifiers passed to setup_requires will be added to the
get_requires_for_build_* function outputs.

Fixes GH #1682

1 files changed, 44 insertions, 1 deletions

diff --git a/setuptools/build_meta.py b/setuptools/build_meta.py
index 047cc07b..fb37c02a 100644
--- a/setuptools/build_meta.py
+++ b/setuptools/build_meta.py
@@ -36,6 +36,8 @@ import contextlib
 import setuptools
 import distutils
 
+from setuptools._vendor import six
+
 __all__ = ['get_requires_for_build_sdist',
            'get_requires_for_build_wheel',
            'prepare_metadata_for_build_wheel',
@@ -51,7 +53,9 @@ class SetupRequirementsError(BaseException):
 
 class Distribution(setuptools.dist.Distribution):
     def fetch_build_eggs(self, specifiers):
-        raise SetupRequirementsError(specifiers)
+        specifier_list = self._parse_requirements(specifiers)
+
+        raise SetupRequirementsError(specifier_list)
 
     @classmethod
     @contextlib.contextmanager
@@ -68,6 +72,45 @@ class Distribution(setuptools.dist.Distribution):
         finally:
             distutils.core.Distribution = orig
 
+    def _yield_lines(self, strs):
+        """Yield non-empty/non-comment lines of a string or sequence"""
+        if isinstance(strs, six.string_types):
+            for s in strs.splitlines():
+                s = s.strip()
+                # skip blank lines/comments
+                if s and not s.startswith('#'):
+                    yield s
+        else:
+            for ss in strs:
+                for s in self._yield_lines(ss):
+                    yield s
+
+    def _parse_requirements(self, strs):
+        """Parse requirement specifiers into a list of requirement strings
+
+        This is forked from pkg_resources.parse_requirements.
+
+        `strs` must be a string, or a (possibly-nested) iterable thereof.
+        """
+        # create a steppable iterator, so we can handle \-continuations
+        lines = iter(self._yield_lines(strs))
+
+        requirements = []
+
+        for line in lines:
+            # Drop comments -- a hash without a space may be in a URL.
+            if ' #' in line:
+                line = line[:line.find(' #')]
+            # If there is a line continuation, drop it, and append the next line.
+            if line.endswith('\\'):
+                line = line[:-2].strip()
+                try:
+                    line += next(lines)
+                except StopIteration:
+                    return
+            requirements.append(line)
+
+        return requirements
 
 def _to_str(s):
     """