Allow superfluous commas in build-dependency lines

This code can interact with handwritten files who can have unneeded
commas for writing easy. As dpkg allows it, we should do as well.

Reported-By: Arnaud Ferraris <arnaud.ferraris@gmail.com>
References: https://lists.debian.org/debian-devel/2021/03/msg00101.html

apt-pkg/deb/debsrcrecords.cc

@@ -123,6 +123,14 @@ bool debSrcRecordParser::BuildDepends(std::vector<pkgSrcRecords::Parser::BuildDe
 
       while (1)
       {
+	 // Strip off leading spaces (is done by ParseDepends, too) and
+	 // superfluous commas (encountered in user-written dsc/control files)
+	 do {
+	    for (;Start != Stop && isspace_ascii(*Start) != 0; ++Start);
+	 } while (*Start == ',' && ++Start != Stop);
+	 if (Start == Stop)
+	    break;
+
 	 BuildDepRec rec;
 	 Start = debListParser::ParseDepends(Start, Stop,
 					     rec.Package, rec.Version, rec.Op, true, StripMultiArch, true);
@@ -141,9 +149,6 @@ bool debSrcRecordParser::BuildDepends(std::vector<pkgSrcRecords::Parser::BuildDe
 	 } else {
 	    BuildDeps.emplace_back(std::move(rec));
 	 }
-
-	 if (Start == Stop)
-	    break;
       }
    }
 

test/integration/test-apt-get-build-dep-file

@@ -108,7 +108,8 @@ Source: apturl
 Section: admin
 Priority: optional
 Maintainer: Michael Vogt <mvo@ubuntu.com>
-Build-Depends: debhelper (>= 7)
+Build-Depends: ,debhelper (>= 7),
+Build-Conflicts: ,,,
 Build-Depends-Indep:
 X-Python3-Version: >= 3.2
 Standards-Version: 3.9.3