scripts: Improve error messages when debian/control has no package stanza

dpkg-gencontrol and dpkg-gensymbols now give a descriptive error message
when no binary package stanza is found in debian/control.

Closes: #642473

Based-on-patch-by: Kyle Willmon <kylewillmon@gmail.com>
Signed-off-by: Guillem Jover <guillem@debian.org>

debian/changelog

@@ -19,6 +19,9 @@ dpkg (1.16.2) UNRELEASED; urgency=low
       the host architecture, for which dpkg itself is not required.
     - Reduces the amount of work performed, including loading and parsing
       unnecessary table files or calling either of gcc or dpkg programs.
+  * Improve error message in dpkg-gencontrol and dpkg-gensymbols when
+    debian/control does not have any package stanza. Closes: #642473
+    Based on a patch by Kyle Willmon <kylewillmon@gmail.com>.
 
   [ Updated dpkg translations ]
   * Italian (Milo Casagrande). Closes: #627832

scripts/dpkg-gencontrol.pl

@@ -152,9 +152,12 @@ if (defined($oppackage)) {
     defined($pkg) || error(_g("package %s not in control info"), $oppackage);
 } else {
     my @packages = map { $_->{'Package'} } $control->get_packages();
-    @packages==1 ||
+    if (@packages == 0) {
+        error(_g("no package stanza found in control info"));
+    } elsif (@packages > 1) {
         error(_g("must specify package since control info has many (%s)"),
               "@packages");
+    }
     $pkg = $control->get_pkg_by_idx(1);
 }
 $substvars->set_msg_prefix(sprintf(_g("package %s: "), $pkg->{Package}));

scripts/dpkg-gensymbols.pl

@@ -155,9 +155,12 @@ if (not defined($sourceversion)) {
 if (not defined($oppackage)) {
     my $control = Dpkg::Control::Info->new();
     my @packages = map { $_->{'Package'} } $control->get_packages();
-    @packages == 1 ||
+    if (@packages == 0) {
+	error(_g("no package stanza found in control info"));
+    } elsif (@packages > 1) {
 	error(_g("must specify package since control info has many (%s)"),
 	      "@packages");
+    }
     $oppackage = $packages[0];
 }