Add tag extension for rpm format version detection

v6 packages have RPMTAG_RPMFORMAT, but we need to differentiate between
3 and 4 too in various places. As such this is a rather simple-minded
heuristic but it at least gives us a central place where to manage that
detection.

docs/manual/tags.md

@@ -456,6 +456,7 @@ Obsoletenevrs         | 5043 | string array | Formatted `name [op version]` obso
 Enhancenevrs          | 5061 | string array | Formatted `name [op version]` enhance dependency strings.
 Recommendnevrs        | 5058 | string array | Formatted `name [op version]` recommend dependency strings.
 Requirenevrs          | 5041 | string array | Formatted `name [op version]` require dependency strings.
+Rpmformat             | 5114 | int32        | Detected rpm format version (3/4/6)
 Suggestnevrs          | 5059 | string array | Formatted `name [op version]` suggest dependency strings.
 Supplementnevrs       | 5060 | string array | Formatted `name [op version]` supplement dependency strings.
 Sysusers              | 5109 | string array | Formatted systemd-sysusers lines for the package. |

lib/tagexts.cc

@@ -1085,6 +1085,22 @@ static int openpgpTag(Header h, rpmtd td, headerGetFlags hgflags)
     return td->count != 0;
 }
 
+static int rpmformatTag(Header h, rpmtd td, headerGetFlags hgflags)
+{
+    if (headerGet(h, RPMTAG_RPMFORMAT, td, HEADERGET_ALLOC))
+	return 1;
+
+    uint32_t *nump = (uint32_t *)xcalloc(1, sizeof(*nump));
+    *nump = headerIsEntry(h, RPMTAG_HEADERIMMUTABLE) ? 4 : 3;
+
+    td->data = nump;
+    td->count = 1;
+    td->type = RPM_INT32_TYPE;
+    td->flags = RPMTD_ALLOCED;
+
+    return 1;
+}
+
 static const struct headerTagFunc_s rpmHeaderTagExtensions[] = {
     { RPMTAG_GROUP,		groupTag },
     { RPMTAG_DESCRIPTION,	descriptionTag },
@@ -1127,6 +1143,7 @@ static const struct headerTagFunc_s rpmHeaderTagExtensions[] = {
     { RPMTAG_SYSUSERS,		sysusersTag },
     { RPMTAG_FILEMIMES,		filemimesTag },
     { RPMTAG_OPENPGP,		openpgpTag },
+    { RPMTAG_RPMFORMAT,		rpmformatTag },
     { 0, 			NULL }
 };