Fix add command with prerelease packages

poetry/console/commands/debug/resolve.py

@@ -11,6 +11,7 @@ class DebugResolveCommand(Command):
 
     debug:resolve
         { package?* : packages to resolve. }
+        { --E|extras=* : Extras to activate for the dependency. }
     """
 
     _loggers = [
@@ -38,9 +39,11 @@ class DebugResolveCommand(Command):
 
             dependencies = []
             for name, constraint in requirements.items():
-                dependencies.append(
-                    Dependency(name, constraint)
-                )
+                dep = Dependency(name, constraint)
+                for ex in self.option('extras'):
+                    dep.extras.append(ex)
+
+                dependencies.append(dep)
 
             package = ProjectPackage(
                 self.poetry.package.name,

poetry/packages/package.py

@@ -123,7 +123,7 @@ class Package(object):
     
     @property
     def full_pretty_version(self):
-        if not self.is_prerelease() and self.source_type not in ['hg', 'git']:
+        if self.source_type not in ['hg', 'git']:
             return self._pretty_version
 
         # if source reference is a sha1 hash -- truncate

poetry/version/version_selector.py

@@ -24,7 +24,10 @@ class VersionSelector(object):
         else:
             constraint = None
 
-        candidates = self._pool.find_packages(package_name, constraint)
+        candidates = self._pool.find_packages(
+            package_name, constraint,
+            allow_prereleases=allow_prereleases
+        )
 
         if not candidates:
             return False
@@ -61,7 +64,9 @@ class VersionSelector(object):
             if parts[0] != 0:
                 del parts[2]
 
-            version = '.'.join([str(p) for p in parts])
+            version = '.'.join(str(p) for p in parts)
+            if parsed.is_prerelease():
+                version += '-{}'.format('.'.join(str(p) for p in parsed.prerelease))
         else:
             return pretty_version