fix patch bump pre release

lib/src/project.dart

@@ -50,7 +50,17 @@ class Project {
       mutation = m.Sequence([mutation, m.SetPreRelease(pre)]);
     }
     final current = await getVersion();
-    final next = mutation(current);
+    Version next = mutation(current);
+    if (next <= current && pre.isNotEmpty && current.isPreRelease) {
+      // pub_semver's nextPatch/nextMinor/nextMajor strip the pre-release suffix
+      // rather than incrementing the numeric component (e.g. 0.0.16-beta →
+      // nextPatch → 0.0.16). When --pre keeps the same identifier the result
+      // equals the current version. Retry against the stripped release so the
+      // numeric component actually advances (0.0.16 → nextPatch → 0.0.17 →
+      // SetPreRelease → 0.0.17-beta).
+      final base = Version(current.major, current.minor, current.patch);
+      next = mutation(base);
+    }
     if (next <= current) {
       throw ArgumentError(
           'The next version must be higher than the current one.');

test/functional_test.dart

@@ -243,6 +243,16 @@ I love my dog.
         expect(err.buffer.toString().trim(),
             'The next version must be higher than the current one.');
       });
+      test('bump patch --pre=beta from pre-release bumps patch number', () async {
+        await run(['version', '0.0.16-beta']);
+        out.buffer.clear();
+        final code = await run(['bump', 'patch', '--pre=beta']);
+        expect(code, 0);
+        expect(err.buffer.toString(), isEmpty);
+        out.buffer.clear();
+        await run(['version']);
+        expect(out.buffer.toString().trim(), '0.0.17-beta');
+      });
       test('incorrect usage', () async {
         final code = await run(['bump']);
         expect(code, 64);