autorelease: improve versioning logic

Consider the following versioning case (rare, but thinkable):
- the previous version has a beta tag
- update_major.txt exists
- update_beta.txt does not exist

The previous code would fail to remove the existing beta tag.
This change fixes the problem. It also adds some comments to make the
logic easier to understand.

setupsrc/pl_setup/autorelease.py

@@ -30,9 +30,9 @@
 )
 
 
-AutoreleaseDir    = join(SourceTree, "autorelease")
-MajorUpdateFile   = join(AutoreleaseDir, "update_major.txt")
-BetaUpdateFile    = join(AutoreleaseDir, "update_beta.txt")
+AutoreleaseDir  = join(SourceTree, "autorelease")
+MajorUpdateFile = join(AutoreleaseDir, "update_major.txt")
+BetaUpdateFile  = join(AutoreleaseDir, "update_beta.txt")
 
 
 def run_local(*args, **kws):
@@ -70,28 +70,38 @@ def do_versioning(latest):
         raise RuntimeError("Neither pypdfium2 code nor pdfium binaries updated. Making a new release would be pointless.")
 
     ver_changes = dict()
+
     if c_updates:
+        # denote pdfium update (independent change)
         ver_changes["V_LIBPDFIUM"] = str(latest)
+
     if inc_major:
-        ver_changes["V_MAJOR"] = VerNamespace["V_MAJOR"]+1
+        # major update
+        ver_changes["V_MAJOR"] = VerNamespace["V_MAJOR"] + 1
         ver_changes["V_MINOR"] = 0
         ver_changes["V_PATCH"] = 0
         os.remove(MajorUpdateFile)
-    else:
-        if v_beta is None:
-            if c_updates:
-                ver_changes["V_MINOR"] = VerNamespace["V_MINOR"]+1
-                ver_changes["V_PATCH"] = 0
-            else:
-                ver_changes["V_PATCH"] = VerNamespace["V_PATCH"]+1
-        elif not inc_beta:
-            ver_changes["V_BETA"] = None
+    elif v_beta is None:
+        # if we're not doing a major update and the previous version was not a beta, update minor and/or patch
+        # however, we still want to run this if adding a new beta tag
+        if c_updates:
+            # pdfium update -> increment minor version and reset patch version
+            ver_changes["V_MINOR"] = VerNamespace["V_MINOR"] + 1
+            ver_changes["V_PATCH"] = 0
+        else:
+            # no pdfium update -> increment patch version
+            ver_changes["V_PATCH"] = VerNamespace["V_PATCH"] + 1
+
     if inc_beta:
+        # if the new version shall be a beta, set or increment the tag (independent change)
         if v_beta is None:
             v_beta = 0
         v_beta += 1
         ver_changes["V_BETA"] = v_beta
         os.remove(BetaUpdateFile)
+    elif v_beta is not None:
+        # if the previous version was a beta but the new one shall not be, remove the tag (independent change)
+        ver_changes["V_BETA"] = None
 
     did_change = set_versions(ver_changes)
     assert did_change