Don't let src.rpm packages to be file signed

File signatures make no sense in source packages as they don't ship
binaries to be installed on the target system, they're just unpacked
into %_topdir for packaging purposes.

Issue a warning instead when attempting to sign a src.rpm but don't fail
the package signing entirely, header signatures are still relevant, as
is the deletion of existing file signatures from a src.rpm.

Resolves: RhBug:2316785

sign/rpmgensig.cc

@@ -702,14 +702,20 @@ static int rpmSign(const char *rpm, int deleting, int flags)
     unloadImmutableRegion(&sigh, RPMTAG_HEADERSIGNATURES);
     origSigSize = headerSizeof(sigh, HEADER_MAGIC_YES);
 
-    if (flags & RPMSIGN_FLAG_IMA) {
-	if (includeFileSignatures(&sigh, &h))
-	    goto exit;
-    }
-
-    if (flags & RPMSIGN_FLAG_FSVERITY) {
-	if (includeVeritySignatures(fd, &sigh, &h))
-	    goto exit;
+    /* Add file signatures (if requested and not a source rpm) */
+    if (!headerIsSource(h)) {
+	if (flags & RPMSIGN_FLAG_IMA) {
+	    if (includeFileSignatures(&sigh, &h))
+		goto exit;
+	}
+	if (flags & RPMSIGN_FLAG_FSVERITY) {
+	    if (includeVeritySignatures(fd, &sigh, &h))
+		goto exit;
+	}
+    } else if (flags & (RPMSIGN_FLAG_IMA | RPMSIGN_FLAG_FSVERITY)) {
+	rpmlog(RPMLOG_WARNING,
+	       _("File signatures not applicable to source packages: %s\n"),
+	       rpm);
     }
 
     if (deleting == 2) {	/* Nuke IMA + fsverity file signature tags. */

tests/rpmsigdig.at

@@ -1845,4 +1845,17 @@ rpm -qp --qf "[%{filenames}:%{filesignatures}\n]" /data/RPMS/imatest-1.0-1.fc34.
 ],
 [ignore])
 
+RPMTEST_CHECK([
+cp /data/SRPMS/hello-1.0-1.src.rpm /tmp/
+rpmsign --key-id 4344591E1964C5FC --addsign --signfiles --fskpath=/data/keys/privkey.pem /tmp/hello-1.0-1.src.rpm
+# Avoid spurious NOKEY warning
+rpmsign --delsign /tmp/hello-1.0-1.src.rpm
+rpm -qp --qf "[%{filenames}:%{filesignatures}\n]" /tmp/hello-1.0-1.src.rpm
+],
+[0],
+[hello-1.0.tar.gz:(none)
+],
+[warning: File signatures not applicable to source packages: /tmp/hello-1.0-1.src.rpm
+])
+
 RPMTEST_CLEANUP