Support major.minor.build versions in <sparkle:minimumSystemVersion>

Previously much less useful major.minor.servicepack was used, which was
of limited practical applicability and is completely useless since
Windows 10.

To preserve backwards compatiblity, treat low values in the 3rd value of
the tuple as service pack version.

NEWS

@@ -1,6 +1,8 @@
 Version 0.8.2
 -------------
 
+- Support major.minor.build versioning scheme in <sparkle:minimumSystemVersion>;
+  previously only much less useful major.minor.servicepack was used.
 - Added support for gzip/deflate-compressed appcasts.
 - Added support for ARM-specific enclosures.
 - Fixed handling of multiple enclosures to correctly pick the most-specific

src/appcast.cpp

@@ -54,12 +54,18 @@ namespace
 
 // Misc helper functions:
 
-bool is_compatible_with_windows_version(const Appcast &item)
+bool is_compatible_with_windows_version(const Appcast &item_)
 {
+    Appcast item(item_);
+
+    item.MinOSVersion = "10";
+
     if (item.MinOSVersion.empty())
         return true;
 
-    OSVERSIONINFOEXW osvi = { sizeof(osvi), 0, 0, 0, 0, { 0 }, 0, 0 };
+    OSVERSIONINFOEXW osvi = {};
+    osvi.dwOSVersionInfoSize = sizeof(osvi);
+
     DWORDLONG const dwlConditionMask = VerSetConditionMask(
         VerSetConditionMask(
         VerSetConditionMask(
@@ -67,8 +73,21 @@ bool is_compatible_with_windows_version(const Appcast &item)
         VER_MINORVERSION, VER_GREATER_EQUAL),
         VER_SERVICEPACKMAJOR, VER_GREATER_EQUAL);
 
-    sscanf(item.MinOSVersion.c_str(), "%lu.%lu.%hu", &osvi.dwMajorVersion,
-        &osvi.dwMinorVersion, &osvi.wServicePackMajor);
+    const int parsed = sscanf(item.MinOSVersion.c_str(), "%lu.%lu.%lu",
+                              &osvi.dwMajorVersion, &osvi.dwMinorVersion, &osvi.dwBuildNumber);
+    if (parsed == 0)
+    {
+        // failed to parse version number, ignore the value
+        return true;
+    }
+
+    // backwards compatibility with WinSparkle < 0.8.2 which used major.minor.sp
+	// instead of major.minor.build for the version number:
+    if (parsed == 3 && osvi.dwBuildNumber < 100)
+    {
+        osvi.wServicePackMajor = static_cast<WORD>(osvi.dwBuildNumber);
+		osvi.dwBuildNumber = 0;
+    }
 
     return VerifyVersionInfoW(&osvi, VER_MAJORVERSION | VER_MINORVERSION |
         VER_SERVICEPACKMAJOR, dwlConditionMask) != FALSE;