Change prerelease default to None (#374)

pex/bin/pex.py

@@ -172,12 +172,12 @@ def configure_clp_pex_resolution(parser, builder):
   group.add_option(
     '--pre', '--no-pre',
     dest='allow_prereleases',
-    default=False,
+    default=None,
     action='callback',
     callback=process_prereleases,
     callback_args=(builder,),
     help='Whether to include pre-release and development versions of requirements; '
-         'Default: only stable versions are used')
+         'Default: only stable versions are used, unless explicitly requested')
 
   group.add_option(
       '--disable-cache',

pex/iterator.py

@@ -22,7 +22,7 @@ def iter(self, req):
 class Iterator(IteratorInterface):
   """A requirement iterator, the glue between fetchers, crawlers and requirements."""
 
-  def __init__(self, fetchers=None, crawler=None, follow_links=False, allow_prereleases=False):
+  def __init__(self, fetchers=None, crawler=None, follow_links=False, allow_prereleases=None):
     self._crawler = crawler or Crawler()
     self._fetchers = fetchers if fetchers is not None else [PyPIFetcher()]
     self.__follow_links = follow_links

pex/package.py

@@ -67,18 +67,20 @@ def raw_version(self):
   def version(self):
     return parse_version(self.raw_version)
 
-  def satisfies(self, requirement, allow_prereleases=False):
+  def satisfies(self, requirement, allow_prereleases=None):
     """Determine whether this package matches the requirement.
 
     :param requirement: The requirement to compare this Package against
     :type requirement: string or :class:`pkg_resources.Requirement`
-    :param bool allow_prereleases: Whether to allow prereleases to satisfy the `requirement`.
+    :param Optional[bool] allow_prereleases: Whether to allow prereleases to satisfy
+      the `requirement`.
     :returns: True if the package matches the requirement, otherwise False
     """
     requirement = maybe_requirement(requirement)
     link_name = safe_name(self.name).lower()
     if link_name != requirement.key:
       return False
+
     # NB: If we upgrade to setuptools>=34 the SpecifierSet used here (requirement.specifier) will
     # come from a non-vendored `packaging` package and pex's bootstrap code in `PEXBuilder` will
     # need an update.

pex/requirements.py

@@ -56,6 +56,8 @@ def requirements_from_lines(lines, builder=None, relpath=None):
       builder.allow_unverified(_get_parameter(line))
     elif line.startswith('--pre'):
       builder.allow_prereleases(True)
+    elif line.startswith('--no-pre'):
+      builder.allow_prereleases(False)
     elif line.startswith('--no-index'):
       builder.clear_indices()
     elif line.startswith('--no-use-wheel'):

pex/resolver.py

@@ -283,7 +283,7 @@ def resolve(
     precedence=None,
     cache=None,
     cache_ttl=None,
-    allow_prereleases=False):
+    allow_prereleases=None):
 
   """Produce all distributions needed to (recursively) meet `requirements`
 
@@ -313,7 +313,7 @@ def resolve(
     resolving inexact requirements will always result in making network calls through the
     ``context``.
   :keyword allow_prereleases: (optional) Include pre-release and development versions.  If
-    unspecified only stable versions will be resolved.
+    unspecified only stable versions will be resolved, unless explicitly included.
   :returns: List of :class:`pkg_resources.Distribution` instances meeting ``requirements``.
   :raises Unsatisfiable: If ``requirements`` is not transitively satisfiable.
   :raises Untranslateable: If no compatible distributions could be acquired for

pex/resolver_options.py

@@ -43,7 +43,7 @@ def __init__(self,
                allow_all_external=False,
                allow_external=None,
                allow_unverified=None,
-               allow_prereleases=False,
+               allow_prereleases=None,
                precedence=None,
                context=None):
     self._fetchers = fetchers if fetchers is not None else [PyPIFetcher()]
@@ -137,7 +137,7 @@ def __init__(self,
                fetchers=None,
                allow_external=False,
                allow_unverified=False,
-               allow_prereleases=False,
+               allow_prereleases=None,
                precedence=None,
                context=None):
     self._fetchers = fetchers if fetchers is not None else [PyPIFetcher()]

tests/test_package.py

@@ -128,3 +128,22 @@ def wheel_package(version):
 
     assert not prerelease_package.satisfies(requirement, allow_prereleases=False)
     assert prerelease_package.satisfies(requirement, allow_prereleases=True)
+
+
+def test_explicit_prereleases():
+  def source_package(version):
+    return SourcePackage('setuptools-%s.tar.gz' % version)
+
+  def egg_package(version):
+    return EggPackage('setuptools-%s-py2.7.egg' % version)
+
+  def wheel_package(version):
+    return WheelPackage('file:///tmp/setuptools-%s-py2.py3-none-any.whl' % version)
+
+  requirement = 'setuptools==7.0b1'
+
+  for package in (egg_package, source_package, egg_package, wheel_package):
+    prerelease_package = package('7.0b1')
+
+    # satisfies should not exclude prereleases if explicitly requested
+    assert prerelease_package.satisfies(requirement)