add special treatment of develop version

lib/spack/spack/concretize.py

@@ -166,7 +166,11 @@ def prefer_key(v):
         valid_versions.sort(key=prefer_key, reverse=True)
 
         if valid_versions:
-            spec.versions = ver([valid_versions[0]])
+            # Disregard @develop and take the next valid version
+            if ver(valid_versions[0]) == ver('develop') and len(valid_versions) > 1:
+                spec.versions = ver([valid_versions[1]])
+            else:
+                spec.versions = ver([valid_versions[0]])
         else:
             # We don't know of any SAFE versions that match the given
             # spec.  Grab the spec's versions and grab the highest

lib/spack/spack/test/versions.py

@@ -92,6 +92,9 @@ def test_two_segments(self):
         self.assert_ver_eq('1.0', '1.0')
         self.assert_ver_lt('1.0', '2.0')
         self.assert_ver_gt('2.0', '1.0')
+        self.assert_ver_eq('develop', 'develop')
+        self.assert_ver_lt('1.0', 'develop')
+        self.assert_ver_gt('develop', '1.0')
 
     def test_three_segments(self):
         self.assert_ver_eq('2.0.1', '2.0.1')

lib/spack/spack/version.py

@@ -236,6 +236,14 @@ def __lt__(self, other):
         if self.version == other.version:
             return False
 
+        # dev is __gt__ than anything but itself.
+        if other.string == 'develop':
+            return True
+
+        # If lhs is dev then it can't be < than anything
+        if self.string == 'develop':
+            return False
+
         for a, b in zip(self.version, other.version):
             if a == b:
                 continue