Fix NpmSpec prerelease-handling.

Thanks to Nathan Walters for spotting this.

Npm ranges with a `<X.Y.Z-P` component were not properly expanded:
they were converted to:
    <X.Y.0 || (>=X.Y.0 && <X.Y.Z-P && no-prerelease)

The correct expansion is:
    <X.Y.0 || (>=X.Y.0-* && <X.Y.Z-P)

Closes #86.

3 files changed, 13 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index 6f63511..1158103 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -4,7 +4,13 @@ ChangeLog
 2.8.3 (unreleased)
 ------------------
 
-- Nothing changed yet.
+*New:*
+    - Add `Clause.prettyprint()` for debugging
+
+*Bugfix:*
+
+    * `#86 <https://github.com/rbarrois/python-semanticversion/issues/86>`_:
+      Fix handling of prerelease ranges within `NpmSpec`
 
 
 2.8.2 (2019-09-06)
diff --git a/semantic_version/base.py b/semantic_version/base.py
index 4327fa1..1b0bac5 100644
--- a/semantic_version/base.py
+++ b/semantic_version/base.py
@@ -1273,7 +1273,7 @@ class NpmSpec(BaseSpec):
                                 prerelease_policy=Range.PRERELEASE_ALWAYS,
                             ))
                         elif clause.operator in (Range.OP_LT, Range.OP_LTE):
-                            prerelease_clauses.append(cls.range(
+                            prerelease_clauses.append(Range(
                                 operator=Range.OP_GTE,
                                 target=Version(
                                     major=clause.target.major,
@@ -1281,6 +1281,7 @@ class NpmSpec(BaseSpec):
                                     patch=0,
                                     prerelease=(),
                                 ),
+                                prerelease_policy=Range.PRERELEASE_ALWAYS,
                             ))
                         prerelease_clauses.append(clause)
                         non_prerel_clauses.append(cls.range(
diff --git a/tests/test_npm.py b/tests/test_npm.py
index 7bed337..da3f5ba 100644
--- a/tests/test_npm.py
+++ b/tests/test_npm.py
@@ -40,6 +40,10 @@ class NpmSpecTests(unittest.TestCase):
             ['1.2.3-alpha.3', '1.2.3-alpha.7', '3.4.5'],
             ['1.2.3-alpha.2', '3.4.5-alpha.9'],
         ),
+        '>1.2.3-alpha <1.2.3-beta': (
+            ['1.2.3-alpha.0', '1.2.3-alpha.1'],
+            ['1.2.3', '1.2.3-beta.0', '1.2.3-bravo'],
+        ),
         '1.2.3 - 2.3.4': (
             ['1.2.3', '1.2.99', '2.2.0', '2.3.4', '2.3.4+b42'],
             ['1.2.0', '1.2.3-alpha.1', '2.3.5'],